6th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2013)

3 Nov 2013, 08:00 → 8 Nov 2013, 18:00 Africa/Johannesburg

Stellenbosch Institute for Advanced Study

Heribert Weigert (University of cape Town) , Will Horowitz (University of Cape Town)

The "6th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2013)" will take place from Nov 4 to Nov 8, 2013 at Stellenbosch Institute for Advanced Studies in Stellenbosch, South Africa, a delightful 30 minute drive into the wine country surrounding Cape Town.  The topics for this Hard Probes conference are:

      • Jet Quenching and Observables

      • High Transverse Momentum Light and Heavy Flavor Hadrons

      • Initial State and Proton-Nucleus Collision Phenomena

      • Heavy Flavor Production and Quarkonia

      • Hard and Thermal Electroweak Probes

 Travel, contact, and other information may be found at the Hard Probes website.

A student summer school will be held prior to the conference.

Registration is now open.   The Early Bird registration deadline is 4 October.

Contact: hp2013@tlabs.ac.za

Sunday, 3 November

17:00 → 20:00 Registration

Monday, 4 November

07:30 → 08:15 Registration

08:15 → 10:30 Plenary

Plenary Session

Convener: Prof. Heribert Weigert (University of cape Town)

08:15 Opening

09:00 Theory: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Prof. Xin-Nian Wang (Lawrence Berkeley National Laboratory)

Slides HP2013-xnwang-pub.pdf

09:30 ALICE: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Francesco Prino (INFN Sezione di Torino)

Slides FPrino-HP13.pdf

10:00 ATLAS: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Dr Peter Steinberg (Brookhaven National Laboratory)

Slides Steinberg_HP2013_v0.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:30 Plenary

Plenary Session

Convener: Prof. Reinhard Stock (Universitaet Frankfurt)

11:00 CMS: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Prof. Julia Velkovska (Vanderbilt University)

Slides HP2013_Velkovska_final.pdf

11:30 STAR: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Frank Geurts (Rice University)

Slides HP2013_Geurts.pdf

12:00 PHENIX: What Have Hard Probes Taught Us about the Quark-Gluon Plasma?

Speaker: Dr Paul Stankus (Oak Ridge National Laboratory)

Slides Final in PDF format

12:30 → 13:30 Lunch

13:30 → 15:30 High Transverse Momentum Light and Heavy Flavor Hadrons

High Transverse Momentum Light and Heavy Flavor Hadrons

Convener: Dr Yves Schutz Schutz (CERN/IN2P3)

13:30 Nuclear Modification Factor and Elliptic Flow of Muons from Heavy-Flavour Hadron Decays in Pb-Pb Collisions at sqrt(s_NN)=2.76 TeV with ALICE

The LHC heavy-ion physics program aims at investigating the properties of strongly- interacting matter in extreme conditions of temperature and energy density, where the formation of the Quark Gluon Plasma (QGP) is expected. In high-energy heavy-ion collisions, heavy quarks are regarded as efficient probes of the properties of the QGP as they are created on a very short time scale in initial hard parton scattering processes and subsequently interact with the medium. In the high transverse momentum region, the suppression of the yield of heavy- flavoured hadrons, quantified by means of the nuclear modification factor, RAA, defined as the ratio of the yield measured in Pb–Pb to that observed in pp collisions scaled with the number of binary nucleon-nucleon collisions, is used to study the heavy quark in-medium energy loss mechanisms. The heavy-flavour elliptic flow, the second order coefficient of the Fourier expansion of particle azimuthal distributions (relative to the reaction plane), pro- vides insight into the degree of thermalization of heavy quarks in the deconfined medium and carries information on the path-length dependence of parton energy loss in the low and high transverse momentum region, respectively. With ALICE, the detector designed and optimized for heavy-ion physics at the LHC, open heavy flavours are measured at forward rapidity (2.5 < y < 4) using semi-muonic decays. The latest results on the nuclear modification factor and elliptic flow of muons from heavy-flavour decays in Pb–Pb collisions at √sNN = 2.76 TeV will be presented. Comparisons with theoretical predictions will be discussed.

Speaker: Dr Gines MARTINEZ GARCIA (SUBATECH)

Slides HP_ShuangLi_v8.pptx

13:50 Heavy-quark azimuthal correlations in heavy-ion collisions

Besides the traditional heavy-quark observables, like the nuclear modification factor and the elliptic flow, azimuthal correlations of heavy quarks and antiquarks have the potential to give new insight into the interactions with the medium. Due to the scatterings with the light medium constituents heavy quarks and antiquarks are deflected from their original direction and the initial correlation of the pair is broadened. We investigate this effect for different transverse momentum classes and find that low-momentum heavy-quark pairs lose their leading order back-to-back initial correlation, while a significant residual correlation survives at large momenta. In the study of two different energy loss scenarios, purely collisional and collisional plus radiative corrections, which both describe the nuclear modification factor and the elliptic flow, we observe that the purely collisional energy loss is more efficient in broadening the initial correlations. This discriminatory feature survives when next-to-leading order production processes are included and offers a fascinating possibility to distinguish the different contributions, collisional and radiative, to the heavy-quark in-medium energy loss once experimental results on azimuthal correlations will be available.

Speaker: Prof. Pol Gossiaux (SUBATECH)

Slides HP_nahrgang.pdf

14:10 Dynamical Evolution, Hadronization and Angular De-correlation of Heavy Flavor in Hot and Dense QCD Matter at RHIC and LHC

Heavy flavor serves as a valuable probe of the transport properties of the quark-gluon plasma created in relativistic heavy-ion collisions. Within the framework of a Langevin equation coupled to a (2+1)-dimensional viscous hydrodynamic model, we introduce an algorithm that incorporates not only collisional, but also radiative energy loss for heavy quarks by treating the medium-induced gluon radiation as a recoil force term for heavy quarks traversing the QGP matter. The subsequent hadronization process is calculated using a hybrid recombination plus fragmentation model. Within this improved transport framework, our calculation shows significant contributions from gluon radiation to heavy quark energy loss at high energies; the recombination mechanism is found important for heavy flavor meson production at intermediate energies. Our numerical results provide a good description of D meson suppression and flow measured at both RHIC and LHC, as well as predictions for the future measurements of B mesons. In addition, a new observable – the angular correlation function of heavy flavor pairs – is explored in our study and found to be a potential candidate for distinguishing different energy loss mechanisms of heavy quarks inside a QGP.

Speaker: Shanshan Cao (Duke University)

Slides 3HF_Dynamics_and_Hadronization.ppt

14:30 Measurements of Open Heavy Flavor Hadrons in STAR Experiment

Heavy flavor quarks are dominantly produced in the initial hard interactions in high energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). Their interaction with QCD medium is sensitive to the medium dynamics. Thus heavy flavor quarks are suggested as an ideal probe to study the properties of the hot and dense nuclear matter created at RHIC. In this talk, we will present recent open heavy flavor measurements by the STAR experiment through both hadronic and semi-leptonic decay channels. We will discuss results of open charm meson and non-photonic electron production cross section measurements in proton-proton and Au+Au collisions at $sqrt{s_NN}$ = 200 GeV. We will also present measurements of open charm mesons in proton-proton collisions at $sqrt{s}$ = 500 GeV and the first result in uranium-uranium collisions at $sqrt{s_{NN}=193$ GeV. Finally we will describe the ongoing Heavy Flavor Tracker and Muon Telescope Detector upgrade projects and their anticipated physics reach in the coming years.

Speaker: Prof. Zhenyu Ye (University of Illinois at Chicago)

Slides yezhenyu_HP2013_20131104_v5.pdf

14:50 D-meson production in pp, p-Pb, and Pb-Pb collisions with ALICE at the LHC

Heavy quarks, i.e. charm and beauty, are considered calibrated probes of the strongly interacting deconfined medium (Quark Gluon Plasma) formed in heavy-ion collisions. Produced in hard scattering processes in the initial stages of the collision, they interact with the medium, lose energy and, depending on the coupling strength to the medium, take part in the collective motion of the QGP matter. ALICE measured the production of D0, D*+, D+ and Ds mesons at central rapidity in pp, p-Pb and Pb-Pb collisions at the LHC. The study of the modification of the transverse-momentum differential yields of charm particles in Pb-Pb collisions with respect to pp collisions, quantified by the nuclear modification factor (RAA), can unravel details of the energy loss mechanism, such as its dependence on the quark mass and on the path length the parton travels through the medium. A similar comparison between pp and p-Pb collision data (RpPb) is fundamental to disentangle effects related to the presence of the hot medium from cold nuclear matter effects, among which nuclear shadowing, suppressing the gluon PDF at low Bjorken-x, is the most important for charm at LHC energies. The degree of thermalization and coupling to the medium is investigated in semi-peripheral Pb-Pb collisions by measuring the elliptic flow coefficient (v2), which quantifies the angular dependence of the particle production with respect to the reaction plane of the collision and, at high pT, is sensitive to the path-length dependence of the energy loss. The latter dependence can be also addressed by studying the modification to the azimuthal correlation distribution of D mesons and charged hadrons in central Pb-Pb collisions with respect to pp collisions. Results on the transverse momentum and centrality dependence of the D-meson elliptic flow and RAA will be presented. The comparison with the RAA of non-prompt J/ψ from B decay measured with CMS will be discussed. The preliminary results on D-meson RpPb and the dependence of D-meson yields on rapidity in p-Pb collisions will be shown. As an outlook, the analysis and the preliminary results on the azimuthal correlations between D-mesons and charged hadrons in pp collisions will be described.

Speaker: Andrea Rossi

Slides 5RossiDmesonsV4.pdf

15:10 Azimuthal Jet Tomography at RHIC and LHC

Recent data on the azimuthal and transverse momentum dependence of high-pT pion nuclear modification factors in nuclear collisions at RHIC and LHC are analyzed in terms of a wide class of jet-energy loss models, ranging from running coupling pQCD based prescriptions to AdS/CFT-inspired models, considering a variety of transverse expanding collective flow backgrounds. RHIC data are found to be surprisingly consistent with rather different dE/dx models. However, extrapolations to LHC favor running coupling QCD based energy-loss models over fixed coupling QCD, conformal AdS holography, or Tc-dominated jet-energy loss models that tend to overpredict jet quenching at the LHC.

Speaker: Dr Barbara Betz (Frankfurt University)

Slides Betz_HP2013.pdf

13:30 → 15:30 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Dr Matthew Lamont (BNL)

13:30 JIMWLK evolution for multi-particle production in Langevin form

We study multi-particle production with rapidity correlations in proton-nucleus collisions at high energy in the Color Glass Condensate framework. The high-energy evolution responsible for such correlations is governed by a generalization of the JIMWLK equation describing the simultaneous evolution of the strong nuclear color fields in the direct amplitude and the complex conjugate amplitude. This functional equation can be used to derive ordinary evolution equations for the cross-sections for particle production but the ensuing equations appear to be too complicated to be useful in practice, even at large Nc. We propose an alternative formulation based on a Langevin process, which is better suited for numerical implementations, and we present the stochastic equations appropriate for two gluon production.

Speaker: Dr EDMOND IANCU (IPhT, Saclay, CEA)

Slides Iancu_HP2013.pdf

13:50 Numerical studies of JIMWLK

In the CGC framework the initial stages of a heavy ion collision at high energy are described as "glasma" field configurations. The initial condition for these evolving fields depends, in the CGC effective theory, on a probability distribution for color charges. The energy dependence of this distribution can be calculated from the JIMWLK renormalization group equation. We discuss recent progress in numerically solving the JIMWLK equation in order to understand properties of the glasma initial state. In particular we discuss work on a practical implementation of the running coupling constant in the Langevin method of solving the JIMWLK equation.

Speaker: Dr Tuomas Lappi (University of Jyväskylä)

Slides lappi_hp13.pdf

14:10 Gluon Saturation Beyond Leading Logs

Speaker: Guillaume Beuf (Universidade de Santiago de Compostela)

Slides GBeuf_HardProbes_2013.pdf

14:30 Study of dijet momentum balance and pseudorapidity distributions in pPb collisions at sqrt{sNN} = 5.02 TeV with CMS

Results on dijet production in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV are presented. Jets are reconstructed with the anti-kT algorithm, using combined information from tracking and calorimetry. The dijet momentum balance, azimuthal angle correlations and pseudorapidity distributions are studied as a function of forward calorimeter transverse energy and compared to results from PYTHIA reference calculations representing pp collisions. For pPb collisions, the dijet momentum ratio pT,2/pT,1 and the width of the azimuthal angle difference distribution is remarkably insensitive to the forward activity of the collision, and comparable to the same quantity obtained from the simulated pp reference. The pseudorapidity of the dijet system changes monotonically with increasing forward calorimeter activity.

Speaker: Doga Gulhan (Massachusetts Institute of Technology)

Slides HP2013_doga.pdf

14:50 Studies of production in the forward region at LHCb

LHCb experiment performs multiple studies at 0.9TeV and 7TeV proton-proton interactions. Results on Energy flow, charge particle multiplicities, particle production ratios, charm production studies are presented and discussed. The comparison with the predictions of different models indicates that more efforts are needed for better understanding of physical processes.

Speaker: Prof. Mikhail Zavertyaev (Max PLank Fuer Kernphysik, Heidelberg)

Slides LHCb-TALK-Hard_Probes-2013-Soth-Africa-Zavertyaev.pdf

15:10 PHENIX Results on Heavy Flavor at Low-x

It is becoming increasingly clear that initial state effects inherent to collisions of nuclei play an important role in the interpretation of data from heavy ion collisions at RHIC and the LHC. Such effects are more apparent in kinematic regions where the gluon density is expected to be significantly modified in the nucleus. The PHENIX experiment has studied these effects through the production of heavy quarks at backwards, middle, and forward rapidity, where partonic interactions in the nucleus and changes in the gluon structure function influence heavy quark production in different ways. Comparisons between these different rapidities in d+Au collisions offer us a window into the dynamics of particle production and transport in the nucleus. In this talk, new PHENIX results on heavy quark production at low x values will be discussed, in the context of A+A data from RHIC and the LHC.

Speaker: Dr J. Matthew Durham (Los Alamos National Lab)

Slides Durham_HardProbes.pptx

13:30 → 15:30 Jet Quenching and Observables

Jet Quenching and Observables

Convener: Mr Peter Jacobs (Lawrence Berkeley National Laboratory)

13:30 Jet quenching in perturbative QCD with JEWEL

I will discuss the present status and prospects for future developments and applications of the (soon publicly available) JEWEL code. JEWEL is a fully microscopic Monte Carlo event generator for jet evolution in a dense, strongly interacting medium. It employs a consistent perturbative approach using a common framework for all scattering and radiation processes. This construction allows for the consistent treatment of recoils, radiation off recoiling scattering centres, multiple gluon emission, interplay between vacuum and medium induced radiation and interferences. At the same time it is very constrained leaving little room for tuning and allowing for a quantitative assessment of uncertainties related to the basic assumptions. Despite its being based on few minimal assumptions JEWEL results are in reasonable agreement with experimental data for both jets and leading hadrons. JEWEL can be interfaced with any model for the medium and thus offers a tool for studying how models implementing different medium properties can be disentangled with the help of hard probes.

Speaker: Korinna Zapp (CERN)

Slides hp13.pdf

13:50 Measurement of jet fragmentation functions and shapes in PbPb collisions at sqrt(sNN)=2.76TeV with CMS

We present measurements of the jet fragmentation functions and transverse momentum profiles (shapes) in PbPb collisions at 2.76 TeV per nucleon-pair center of mass energy with the CMS detector. Jets are reconstructed by the anti-kT sequential clustering algorithm with a resolution parameter of 0.3, using particle-flow objects that combine tracking and calorimetric information. In this talk the jet properties of inclusive jets with transverse momentum pT > 100 GeV/c in PbPb collisions are measured for reconstructed charged particles with pT > 1 GeV/c in a cone of radius sqrt((Δ φ)^2 + ( Δ η)^2)=0.3 around the jet axis. A data sample of PbPb collisions collected in 2011 at a center-of-mass energy of sqrt{sNN}= 2.76 TeV corresponding to an integrated luminosity of 150 µb^-1 is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on the full 2013 pp statistics collected at the same collision energy. Centrality-dependent modifications of the fragmentation functions and shapes are revealed.

Speaker: Dr Yaxian MAO (Vanderbilt University)

Slides YMAO_JSandJFF_HP2013v4.pdf

14:10 Jet suppression in Pb+Pb collisions with the ATLAS detector

Speaker: Mr Martin Rybar (Charles University)

Slides HP2013_Rybar.pdf

14:30 Probabilistic picture for in-medium jet evolution

We study the evolution of a high energy jet triggered by its interactions with a dense QCD medium. We show that the relatively components of the jet which propagate at large angles can be described as the products of a classical branching process, in which successive branchings proceed independently from each other. This exploits the fact that the in-medium rescattering is very efficient in destroying the color coherence between the soft emitted partons: this coherence is washed out already during the branching process, that is, over time scales which are much shorter than the size L of the medium. This allows us to construct a master equation for the generating functional encoding all the intra-jet multi-parton distributions (that is, the distributions in energies and in angles). The `jet quenching parameter' $\hat q$, which is the only medium-dependent parameter in this description, receives large radiative corrections from a different type of radiation --- namely, from hard gluon emissions which are triggered by a single scattering in the medium and occur on time scales much shorter than the typical branching time alluded to above.These radiative corrections, enhanced by a double logarithm $\alpha_s \log^2 (L T)$ with $T$ the temperature of the medium, are strongly ordered and overlapping in formation time. We show that these coherent branchings can be absorbed into a renormalization of the jet quenching parameter without spoiling the probabilistic picture mentioned above and which involves only incoherent branchings. arXiv:1209.4585 [hep-ph] JHEP 1301 (2013) 143 arXiv:1307.xxxx [hep-ph] In preparation

Speaker: Dr Yacine Mehtar-Tani (IPhT Saclay)

Slides Mehtar-HP2013.pdf

14:50 Jet propagation within a Linearized Boltzmann Transport Model

A Linearized Boltzmann Transport model is developed for the study of parton propagation inside quark-gluon plasma. Both leading partons and thermal recoiled partons are tracked so that one can also study jet-induced medium excitation. In this study, we implement the complete set of elastic parton scattering processes and investigate elastic parton energy loss, transverse momentum broadening and their nontrivial energy and length dependence. We further investigate the jet shape and fragmentation functions of reconstructed jets using FASTJET algorithm. Contributions from the recoiled thermal partons are found to have significant influences on jet shape and angular distribution of reconstructed jets.

Speaker: Mr Tan Luo (Central China Normal University)

Slides HP2013-LuoTan.pdf

15:30 → 16:00 Coffee Break

16:00 → 18:00 Heavy Flavor Production and Quarkonia

Heavy Flavor Production and Quarkonia

Convener: Prof. William Brooks

16:00 PHENIX charmonia: what have we learned?

PHENIX has good quality measurements from Au+Au, Cu+Cu, p+p and d+Au collisions, and the analysis of data from Cu+Au and U+U collisions is nearing completion. The analysis of charmonium data from the 2008 d+Au run has recently been completed, and this talk will focus on what we have learned from the d+Au data about the mechanisms that modify charmonium production in a nucleus. The d+Au charmonium data from PHENIX consist of 1) J/psi modification versus centrality across the full PHENIX rapidity range, and 2) psi' data at midrapidity only. Both show unexpected features. The J/psi modification at forward rapidity requires a stronger than linear dependence of suppression on nuclear thickness, while the psi' suppression for central collisions is unexpectedly stronger than that for the J/psi. There will be a discussion of the implications of the rapidity dependence and of the centrality dependence, and also of why we believe that the centrality measurement is reliable. It has long been assumed that that p(d)+A data provide the baseline for measuring hot nuclear matter effects in A+A collisions by isolating the "cold nuclear matter" effects. However recent results from p+Pb at the LHC and d+Au at RHIC show correlations of soft particles across large rapidity gaps that are consistent with flow. This raises the possibility that there are hot matter effects in d+Au collisions that may affect charmonium production, and evidence for and against this will be discussed.

Speaker: Dr Anthony Frawley (Forida State University)

Slides 1-Frawley_HP2013_PHENIX_charmonium.pdf 1-Frawley_HP2013_PHENIX_charmonium.pdf

16:20 Upsilon production measurements with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) is designed to study ultra-relativistic heavy-ion collisions, where strongly interacting matter is produced and a phase transition to the Quark Gluon-Plasma (QGP) is expected. Quarkonia resonances are considered to be one of the most promising probes of the deconfined phase, since the heavy quark pairs are produced in the early stages of the collision and their bound states are sensitive to the QGP temperature. Unlike charmonium, regeneration effects at hadronisation are not expected to play a major role on bottomonium production. Cold nuclear matter effects can be distinguished from the hot nuclear matter ones by studying bottomonium production in proton-nucleus collisions, where no deconfined state is expected to be created. In ALICE, $\Upsilon$ production can be measured in the muon decay channel with the forward muon spectrometer ($2.5

Speaker: Francesco Bossu (iThemba LABS, Cape Town)

Slides 2-Bossu_hp_bossu.pdf

16:40 Bottomonium production in pp, pPb, and PbPb collisions with CMS

The three Y states (1S, 2S, 3S) were measured separately using the Compact Muon Solenoid (CMS) experimental apparatus via their dimuon decays in pp and pPb collisions, in the rapidity range |y|<1.9 in the centre-of-mass of the collision. The datasets used in the analysis correspond to recorded integrated luminosities of about 31/nb (pPb) and 5.1/pb (pp), collected in 2013 by the CMS experiment at the LHC, at a centre-of-mass energy per nucleon-nucleon pair of 5.02 TeV and 2.76 TeV respectively. Results of the production ratios of the excited states, Y(2S) and Y(3S), with respect to the ground state Y(1S) will be presented in the context of the PbPb results.

Speaker: Dr Dong Ho Moon (University of Illinois at Chicago)

Slides 3-Moon_HP2013_dmoon_draft_v8.pdf HP2013_dmoon_draft_v10.pdf

17:00 Lattice calculation of the heavy quark potential at T>0

I discuss new results on the extraction of the heavy quark anti-quark potential at non-zero temperature from lattice QCD. Calculations have been performed using Highly Improved Staggered Quark action on lattices with temporal extent Nt=6, 8 and 12. The potential is extracted from the temporal Wilson loops, largely extending the first preliminary calculations using Nt=6 lattices [1]. Implications of the findings for the quarkonium spectral function will be discussed. [1] A. Bazavov and P. Petreczky, Nucl. Phys. A904-905 (2013) 599c

Speaker: Peter Petreczky (BNL)

Slides petreczky_hp13.pdf petreczky_hp13.pptx

17:20 Investigating Jet Quenching on the Lattice

Due to the dynamical, real-time, nature of the phenomenon, the study of jet quenching via lattice QCD simulations is not straightforward. In this talk, however, it will be shown how it is possible to extract information about the momentum broadening of a hard parton moving in the quark-gluon plasma, from lattice simulations. After discussing the basic idea (originally proposed by Caron-Huot), we will present a recent study, in which we estimated the jet quenching parameter non-perturbatively, from the lattice evaluation of a particular set of gauge-invariant operators.

Speaker: Marco Panero (University of Helsinki)

Slides hardprobes2013.pdf

17:40 Azimuthal Jet Flavor Tomography via CUJET with Running Coupling in 2+1D Viscous QGP Fluids

We present recent progress with the CUJET pQCD jet tomographic model, which couples running coupling dynamic DGLV opacity series with 2+1D viscous hydro $(T,u^\mu)$ fields. We test the consistency of this model with recent RHIC and LHC data on the azimuthal and transverse dependence of $R_{AA\rightarrow h} (p_T, \phi, \sqrt{s}, b)$, the nuclear modification of light and heavy open flavor fragments from quenched jets.

Speaker: Jiechen Xu (Columbia University)

Slides Hard_Probes_2013_Jiechen_Xu.pdf

16:00 → 18:00 High Transverse Momentum Light and Heavy Flavor Hadrons

High Transverse Momentum Light and Heavy Flavor Hadrons

Convener: Prof. Harald Appelshauser (University of Frankfurt)

16:00 A transport set-up for heavy-flavour observables in nucleus-nucleus collisions at RHIC and LHC

A multi-step setup for heavy-flavour studies in high-energy nucleus-nucleus collisions is presented. The initial hard production of Q-Qbar pairs is simulated with the POWHEG pQCD event generator, interfaced with the PYTHIA parton shower. Outcomes of the calculations are compared to experimental data in p-p collisions and are used as a validated benchmark for the study of medium effects. In the nucleus-nucleus case, the propagation of the heavy quarks in the medium is described through the relativistic Langevin equation. The numerical results are compared to experimental data from RHIC and the LHC. In particular we show the comparisons for the nuclear modification factor and for the elliptic flow coefficient v_2 of D/B mesons and heavy-flavor electrons. Besides the results already appeared in Eur. Phys. J. C (2013) 73:2481, we will show a new comparison with data on non-prompt J/psi's from CMS and ALICE, which will are becoming available. Furthermore, a more systematic study of the effects of heavy-flavor hadronization will be presented.

Speaker: Dr Marzia Nardi (INFN Torino)

Slides 1HP2013_Nardi.pdf

16:20 Interplay between bulk medium evolution and (D)GLV energy loss

The PHENIX Collaboration has argued that azimuthal angle dependent pi0 suppression in Au+Au at RHIC poses a challenge for perturbative QCD energy loss models. However, recent work by Betz and Gyulassy claims simultaneous reproduction of this set of observables with simple pQCD-motivated energy loss formulas. We study and contrast different bulk medium evolution models (based on hydrodynamics and covariant transport) combined with different implementations of Djordjevic-Gyulassy-Levai-Vitev radiative energy loss to investigate whether, and if yes then how the nuclear-suppression vs elliptic flow puzzle could be resolved in the DGLV framework for light partons and heavy quarks. This is especially interesting in view of our earlier results that showed that realistic transverse expansion of the bulk medium reduces high-pT elliptic flow from GLV energy loss by nearly half compared to transversely frozen evolution scenarios.

Speaker: Dr Denes Molnar (Purdue University)

Slides 2hp2013.pdf

16:40 Identified particle production in sqrt(sNN)=2.76 TeV pp and Pb-Pb collisions with ALICE at the LHC

ALICE has unique capabilities among the LHC experiments for particle identification (PID) at mid-rapidity over a wide range of transverse momentum ($p_{\rm T}$). For $p_{\rm T}$ between $\sim 100$ MeV/$c$ up to 3-4 GeV/$c$ (anti)protons, charged pions and kaons can be separated through the measurement of the specific energy loss (${\rm d}E/{\rm d}x$) in gas (silicon) with TPC (ITS) and time of flight (TOF). The identification can be extended to higher $p_{\rm T}$ by using a Cherenkov detector (HMPID). For $3 < p_{\rm T} < 20$ GeV/$c$, statistical PID is possible thanks to the relativistic rise of the ${\rm d}E/{\rm d}x$ in the TPC. In this talk results on the transverse momentum distributions ($\sim0.3

Speaker: Dr Antonio Ortiz Velasquez (Div. of Particle Physics, Lund University, Sweden)

Slides aortizve_hp2013.pdf

17:00 Medium-induced gluon radiation beyond the eikonal approximation

In this work we improve existing calculations of radiative energy loss by computing corrections that implement energy-momentum conservation, previously only implemented a posteriori, in a rigorous way. Using the path-integral formalism, we compute in-medium splittings allowing transverse motion of all particles in the emission process, thus relaxing the assumption that only the softest particle is permitted such movement. This work constitutes the extension of the computation carried out for x → 1 in Phys. Lett. B718 (2012) 160-168, to all values of x, the momentum fraction of the energy of the parent parton carried by the emitted gluon. In order to accomplish a general description of the whole in-medium showering process, in this work we allow for arbitrary formation times for the emitted gluon (the limit of small formation times was previously employed in [J.-P. Blaizot, F. Dominguez, E. Iancu, and Y. Mehtar-Tani, JHEP1301 (2013) 143], for the g → gg splitting). We provide general expressions and their realisation in the path integral formalism within the harmonic oscillator approximation.

Speaker: Liliana Apolinário (Universidade de Santiago de Compostela)

Slides LApolinario.pdf

17:20 The parton cascade BAMPS with the improved Gunion-Bertsch matrix element

An updated version of the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS) is presented, which allows interactions among all partons: gluons, light quarks, and heavy quarks with elastic and inelastic collisions. We introduce the improved Gunion-Bertsch matrix element, which cures problems of the original Gunion-Bertsch result in characteristic regions of the phase space. Verified by extensive numerical calculations, the improved matrix element agrees well with the exact calculation. With the new matrix element, important properties of the quark-gluon-plasma in heavy-ion collisions such as the thermalization time of the plasma and the shear viscosity over entropy density ratio are calculated within the microscopic transport model BAMPS. Furthermore, we compare our results of the nuclear modification factor and elliptic flow to experimental data at RHIC and LHC.

Speaker: Carsten Greiner (Goethe University Frankfurt)

Slides hardprobe_2013_greiner.pdf

17:40 Detail study of the medium created in Au+Au collisions with high pT probes by the PHENIX experiment at RHIC

PHENIX has been measuring high pT identified hadrons such as pi0 or eta since the beginning of the RHIC running. These measurements along with the baseline direct photon measurement led to the discovery of parton energy loss, a final state interaction with a medium, the quark-gluon plasma. After accumulation of additional statistics in recent RHIC Au+Au runs, we were able to not only reduce uncertainties of golden channel measurements (e.g. pT spectra), but also extend the degree of freedom, such as the yield versus emission angle w.r.t event planes. Detailed analysis of these measurements provided us deeper insight of the characteristics of the quark-gluon plasma. We have studied the average fractional energy loss (dE/E) of hadrons, as well as the path-length dependence of the energy loss. We have also measured higher order harmonic flows of high pT hadrons that would improve understanding of the medium from hydrodynamic point of view. In this presentation, the recent high pT hadron results obtained by the PHENIX experiment will be shown, and the physics learned from the results will be discussed in detail.

Speaker: Dr Takao Sakaguchi (Brookhaven National Laboratory)

Slides Sakaguchi_HP2013.pdf Sakaguchi_HP2013.pptx

16:00 → 18:00 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Dr Paul Stankus (Oak Ridge National Laboratory)

16:00 Azimuthal anisotropy v_2 in U+U collisions at STAR

The azimuthal anisotropy of particle production is commonly used in high-energy nuclear collisions to study the early evolution of the expanding system. The prolate shape of uranium nuclei provides the possibility to study how the initial geometry of the nuclei affects the azimuthal distributions. It also provides a unique opportunity to understand the initial condition for particle production at mid-rapidity in heavy ion collisions. In this talk, the two- and four- particle cumulant, $v_2$($v_2{2}$ and $v_2{4}$), from U+U collisions at $\sqrt{s_{NN}}=$ 193 GeV and Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV for inclusive charged hadrons will be presented. The STAR Zero Degree Calorimeters resolution allows to further separate more central collisions within 0-1% centrality bin. Differences were observed between the multiplicity dependence of $v_2{2}$ for most central Au+Au and U+U collisions. The observed $v_2{2}$ slope results were compared to Monte Carlo Glauber model predictions and it was seen that this model cannot explain the present results on the multiplicity dependence of $v_2{2}$ in central collisions.

Speaker: Dr Paul Sorensen (BNL)

Slides Sorensen_UU_v2_for_hard_probes.pptx

16:20 Transverse momentum and pseudorapidity dependence of charged particle production and nuclear modification factor in pPb collisions at sqrt(sNN)=5.02 TeV with CMS

The charged particle transverse momentum (pT) spectra at midrapidity and forward pseudorapidity ranges up to pT=100 GeV/c are presented for pPb collisions at sqrt(sNN)=5.02 TeV. The nuclear modification factor (RpPb) is measured at midrapidity by dividing the measured pPb spectrum by a pp reference spectrum constructed using interpolation methods. In addition, the asymmetries in the charge particle yields between equivalent positive and negative pseudorapidity ranges in both the laboratory and center-of-mass frames are presented as a function of pT.

Speaker: Krisztian Krajczar (CERN)

Slides HP2013_Krajczar_v3.pdf

16:40 The Initial Flow of Gluon Fields and Its Implications for Heavy Ion Collisions

We calculate the energy flow of the quasi-classical gluon field at early times in high energy nuclear collisions. We argue that the transverse flow has a rapidity-even component that is similar to collective flow in a fluid and emerges from the QCD analog of Farady's and Ampere's Law, and it has a rapidity-odd component that can be understood from Gauss' Law for gluon fields. While the former leads to the usual radial and elliptic flow phenomena, the rapidity-odd flow term implies directed flow and leads to characteristic flow patterns in asymmetric systems like Cu+Au. A comprehensive study of these unique flow phenomena could lead to novel signatures of color glass. We also discuss a method to calculate initial conditions for a further viscous hydrodynamic evolution from the full energy momentum tensor of the gluon field. This allows us to calculate the phenomenological consequences of the initial gluon field flow. In particular, we show that color glass predicts a rotation of the fireball around the impact vector axis.

Speaker: Prof. Rainer Fries (Texas A&M University)

Slides Hard_Probes_2013.pptx

17:00 The onset of hydrodynamical flow in high energy heavy ion collisions

Real time lattice simulations of the early stages of high energy collisions in the Color Glass Condensate framework indicate a rapid isotropization of the pressure tensor. For realistic values of the saturation momentum, nearly ideal hydrodynamics provides a good description of the bulk evolution of the system after a transient regime that lasts about 1 fermi/c.

Speaker: Mr Thomas Epelbaum (IPhT, CEA-Saclay)

Slides Epelbaum_HP_04_11.pdf

17:20 Anisotropic flow of thermal photons as a quark-gluon plasma viscometer

As is well known, photons are a penetrating probe of the dense medium created in heavy-ion collisions. I will present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics. Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their $p_T$-differential anisotropic flow coefficients $v_n(p_T)$ are computed, both with and without accounting for viscous corrections to the standard thermal emission rates at leading logarithmic order. Viscous corrections to the rates are found to have a larger effect on the $v_n$ coefficients than the viscous suppression of hydrodynamic flow anisotropies. Since photons are found to be more sensitive to the quark-gluon plasma (QGP) shear viscosity than hadrons, their anisotropic flow coefficients $v_n$ serve as a sensitive QGP viscometer.

Speaker: Mr Chun Shen (The Ohio State University)

Slides Shen_HP2013_photon_vn.pdf

17:40 From full stopping to transparency in a holographic model of heavy ion collisions

We numerically simulate planar shock wave collisions in anti-de Sitter space as a model for heavy ion collisions of large nuclei. We uncover a cross-over between two different dynamical regimes as a function of the collision energy. At low energies the shocks first stop and then explode in a manner approximately described by hydrodynamics, in close similarity with the Landau model. At high energies the receding fragments move outwards at the speed of light, with a region of negative energy density and negative longitudinal pressure trailing behind them. The rapidity distribution of the energy density at late times around mid-rapidity is not approximately boost-invariant but Gaussian, albeit with a width that increases with the collision energy.

Speaker: Dr Jorge Casalderrey-Solana (Universitat de Barcelona)

Slides jcstalk.pdf

18:00 → 19:00 Reception

Tuesday, 5 November

08:30 → 10:00 Plenary

Plenary Session

Convener: Dr Marco van Leeuwen (Nikhef)

08:30 Jet Physics Theory

Speaker: Carlos Salgado (Universidade de Santiago de Compostela)

Slides HardProbes2013-salgado.pdf

09:00 Fully Reconstructed Charged Jets in Central Au+Au Collisions at sqrt(s_NN)=200 GeV from STAR

Speaker: Jan Rusnak (Nuclear Physics Institute, Academy of Sciences of the Czech Republic)

Slides rusnak_hardprobes_final.pdf

09:30 Jet production and structure in pp, p-Pb and Pb-Pb collisions measured by ALICE

Speaker: Dr Rosi Reed (Yale)

Slides RReedHP2013Jetsv4.pdf

10:00 → 10:30 Coffee Break

10:30 → 12:30 Plenary

Plenary Session

Convener: Prof. Gunther Roland (MIT)

10:30 From Jet Quenching to Wave Turbulence

Speaker: Dr Edmond Iancu (IPhT Saclay)

Slides iancu_plenary.pdf

11:00 Jet measurements from the CMS Collaboration

Speaker: Yue Shi Lai (Massachusetts Institute of Technology)

Slides hp-20131103.pdf

11:30 Measurement of jet structure in Pb+Pb collisions using the ATLAS detector

Speaker: Dr Aaron Angerami (Columbia University)

Slides angerami_HP2013.pdf

12:00 ALICE results on the production of light-flavor hadrons at the LHC

Speaker: Jacek Otwinowski (GSI Helmholtz Centre for Heavy Ion Research)

Slides HardProbes2013_JacekOtwinowski_final.pdf

12:30 → 13:30 Lunch

13:30 → 15:30 Hard and Thermal Electroweak Probes

Hard and Thermal Electroweak Probes

Convener: Dr Enrico Scomparin (INFN Torino (Italy))

13:30 Measurements of direct photons in AuAu collisions with PHENIX

The PHENIX experiment has published direct photon yields and elliptic flow coefficients (v2) from Au+Au collisions at RHIC energies. These results have sparked much theoretical discussion. The measured yields and flow parameters are difficult to reconcile in current model calculations of thermal radiation based on hydrodynamic time evolution of the collision volume. New sources of photons, e.g. initial state emission related to strong magnetic fields, have been proposed as alternatives. Our latest analyses which use high statistics data from Run-7 and Run-10 allow to determine yields and harmonic coefficients (v_n) with finer granularity in centrality and photon momentum and down to p_T as low as 400 MeV/c. In this talk we will summarize the current status and present new results from PHENIX.

Speaker: Benjamin Bannier (Stony Brook University)

Slides slides.pdf

13:50 Low mass dilepton production in pp, p-Pb and Pb-Pb collisions measured with ALICE at the LHC

Low mass dilepton production, including light vector mesons ρ, ω, φ, provides key information on the hot and dense state of strongly inter- acting matter produced in high-energy heavy-ion collisions. Among them, strangeness production can be studied through the measure- ment of φ meson production, while the detailed description of the full dilepton mass spectra down to the kinematic threshold can be used to reveal in-medium modifications of hadron properties and the ther- mal emission arising from the medium. Measurements in pp and p-A systems, in absence of hot nuclear matter effects, can be used as a ref- erence to test our knowledge of the processes expected to contribute to dilepton production. Dilepton production is studied with the ALICE apparatus at the LHC both at central (|y| < 0.9) and forward (2.5 < y < 4) rapidities, respectively in the dielectron and dimuon channel. Results on low mass dilepton production are shown, for various c.m. energies, in pp, p-Pb, Pb-p and Pb-Pb collisions.

Speaker: Antonio Uras (Universite Claude Bernard-Lyon I)

Slides 2-Alice_HardProbes2013_Uras_v2.pdf

14:10 Photon Signals from Quarkyonic Matter

This contribution will present a novel way to experimentally investigate quarkyonic matter. In order to do so we calculate the Bremsstrahlung photon spectrum emitted from dynamically evolving quarkyonic matter, and compare this spectrum with that of a high chemical potential quark-gluon plasma as well as to a hadron gas. We find that the transverse momentum distribution and the harmonic coefficient is markedly different in the three cases. The quarkyonic elliptic flow coefficient fluctuates randomly from event to event, and within the same event at different transverse momenta. The latter effect, which can be explained by the shape of quark wavefunctions within quarkyonic matter, might be considered as a quarkyonic matter signature. The corresponding manuscript has been accepted for publication in PRL and can be found at http://arxiv.org/abs/arXiv:1302.1119.

Speaker: Dr Sascha Vogel (Frankfurt Institute for Advanced Studies)

Slides 3-HardProbes2013_svogel.pdf

14:30 Electromagnetic radiation as a probe of the initial state in relativistic nuclear collisions and of viscous hydrodynamics

The penetrating nature of electromagnetic signals makes them suitable probes to explore the properties of the strongly-interacting medium created in relativistic nuclear collisions. This study investigates thermal electromagnetic radiation production using a 3+1D viscous hydrodynamic simulation (MUSIC). We study the thermal dilepton/photon emission of the medium by using both pQCD and hadronic scattering (and decay) processes. We will examine the effects of the initial conditions, viscosity, and event-by-event fluctuations on the flow coefficients of electromagnetic probes.

Speaker: Mr Gojko Vujanovic (McGill University)

Slides Vujanovic_Hard_Probes_2013_v23.pdf

14:50 Dileptons in d+Au Collisions at sqrt(s)=200 GeV measured by PHENIX and its implications on heavy flavor

The dielectron mass spectrum is a unique probe to directly access the different stages of a heavy-ion collision. The low mass region (m_ee < 1 GeV/c^2) reflects the Quark Gluon Plasma (QGP) temperature and thermalization phase, while the low vector meson resonances probe chiral symmetry restoration. The intermediate (1< m_ee<3 GeV/c^2) and high (4

Speaker: Dr Deepali Sharma (Stony Brook University)

Slides hardprobes_2013_talk.pdf

15:10 On loop corrections to the dilepton rate

A novel next-to-leading order analysis of the dilepton production rate from a hot QCD plasma is reported. The photon invariant mass is taken to be in the range K^2 ~ (pi T)^2; subsequently the results are compared with an OPE computation in a hard regime K^2 >> (pi T)^2, with an LPM resummed computation in a soft regime K^2 << (pi T)^2, as well as with recent lattice simulations in the Euclidean domain.

Speaker: Mr Mikko Laine (University of Bern)

Slides hp13.pdf

13:30 → 15:30 High Transverse Momentum Light and Heavy Flavor Hadrons

High Transverse Momentum Light and Heavy Flavor Hadrons

Convener: Karel Safarik (CERN)

13:30 Heavy quark quenching and elliptic flow from RHIC to LHC: can the experimental results be understood by pQCD?

Recently, we have proposed a microscopic approach for the quenching and thermalisation of heavy quarks (HQ) in URHIC \cite{Gossiaux:2008,Gossiaux:2009,Gossiaux:2010,Gossiaux:2011}, assuming that they interact with light partons through both elastic and radiative processes evaluated by resorting to some parameterization of the running coupling constant, while those partons are spatially distributed along the hydrodynamical evolution of the hot medium. This approach is able to explain successfully several observables measured at RHIC and LHC, such as the nuclear modification factor and the elliptic flow of open heavy flavor mesons and non-photonic single electrons. The diffusion coefficient of heavy quarks in the quark gluon plasma -- a fundamental property of this state of matter -- can thus be extracted and compared with recent lattice calculations. In this contribution, we provide a general overview of our MC@HQ event generator which can presently be coupled to the hydrodynamical evolution of the plasma as realized by the KOLb-Heinz approach or by the EPOS model. We discuss the influence of the different hydrodynamical evolution on the predictions for heavy mesons. We confront the results of our model for D and B mesons as well as for the lepton production in URHIC with experimental results obtained so far by the various collaborations at RHIC and LHC. Perspectives for future observables like correlations will be proposed. % \begin{thebibliography}{9} \bibitem{Gossiaux:2008} P.B. Gossiaux, J. Aichelin, Phys. Rev. C{\bf 78}, 014904 (2008), [hep-ph/0802.2525]. \bibitem{Gossiaux:2009} P.B. Gossiaux, R. Bierkandt, J. Aichelin, Physical Review C{\bf 79} (2009) 044906 \bibitem{Gossiaux:2010} P.B. Gossiaux, V. Guiho, J. Aichelin, J. Phys. G: Nucl. Part. Phys. {\bf 37} (2010) 094019 \bibitem{Gossiaux:2011} P.B. Gossiaux et al., Accepted for publication in Nuclear Physics A [arXiv:1209.0844]

Speaker: Dr Pol Gossiaux (subatech)

Slides 1_HP_gossiaux.pdf

13:50 Elastic vs. radiative heavy quark energy loss within a transport model

The full space-time evolution of heavy quarks and light partons in ultra-relativistic heavy-ion collisions is studied within the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). We discuss in detail for all flavors the influence of elastic and radiative energy loss with a running coupling. Radiative processes, in particular, are implemented through an improved version of the Gunion-Bertsch matrix element, which is derived from comparisons to the exact result. In this calculation the finite heavy quark masses are explicitly taken into account, leading to the dead cone effect. Consequently, we present results of this updated version of BAMPS and compare them to experimental data at RHIC and LHC. In detail, the nuclear modification factor and elliptic flow of charged hadrons, heavy flavor electrons as well as muons, D mesons, and non-prompt J/psi are discussed. The latter two are especially sensitive to the mass difference of charm and bottom quarks. Furthermore, we make predictions where no data is available yet.

Speaker: Jan Uphoff (Goethe University Frankfurt)

Slides 2-jan_uphoff_hp13.pdf

14:10 Measurement of b-jet fraction and nuclear modification factors in PbPb collisions at sqrt{sNN}= 2.76 TeV with CMS

Modification to jets in high-energy heavy-ion collisions is expected to depend on the flavor of the fragmenting parton. To disentangle this flavor dependence, jets from heavy quark fragmentation are identified in heavy ion collisions. Jets are first tagged by their secondary vertices and the contribution from bottom quarks is extracted using template fits to their secondary vertex mass distributions. The bottom quark jet to inclusive jet ratio is measured with the CMS detector from PbPb and pp collisions at a center-of-mass energy of 2.76 TeV per nucleon. In this talk, the inclusive b-jet fraction and nuclear modification functions measured in the range of 60 < jet pT < 200 GeV/c, using full 2011 PbPb and 2013 pp data collected at sqrt{s}=2.76 TeV are presented.

Speaker: Kurt Jung (Purdue University)

Slides HP2013-kjung-BJetRAA-Final.pdf

14:30 Measurements of electrons from heavy-flavour decays in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

Heavy-ion collisions at the LHC provide an opportunity to investigate the properties of QCD matter at high temperatures and energy densities, where a transition to a Quark- Gluon Plasma state is expected to occur. In order to study the QGP properties, a given observable is often measured in different collision systems (pp, p-Pb and Pb-Pb) and multiplicity classes. Heavy quarks, i. e. charm and beauty, are a powerful probe for this state of matter. Due to their large masses, they are produced in initial hard parton scattering processes, and they propagate through the hot and dense medium created in the collision of heavy ions. Heavy-flavour hadrons can be studied via the measurement of electrons from their semi-electronic decays. ALICE has excellent capabilities for heavy-flavour measurements employing several sub- systems providing high resolution vertex and track reconstruction, as well as particle iden- ti􏷯cation in a wide momentum range. In this contribution, measurements of the nuclear modification factors (RpPb and RAA) and of the elliptic flow v2, of heavy-flavour decay electrons, will be presented as a function of pT. The nuclear modification factor is the ratio of the electron transverse momentum spectrum measured in Pb-Pb (p-Pb) collisions to that in pp collisions, scaled by the number of binary nucleon-nucleon collisions. The elliptic flow v2 is the second Fourier coefficient of the azimuthal distribution of particle momenta in the transverse plane with respect to the reaction plane. Furthermore, studies of the correlation between these electrons and unidentified charged particles in pp (√s = 2.76 TeV), p-Pb (√sNN = 5.02 TeV) and Pb-Pb (√sNN = 2.76 TeV) collisions will be reported.

Speaker: Elienos Pereira De Oliveira Filho

Slides 4-hp2013-elienos.pdf

14:50 Shooting string holography of jet quenching at RHIC and LHC

Previous holographic models of jet quenching in AdS/CFT via “falling strings” were found to be incompatible with the recent LHC data in arXiv:1208.0305. A new set of “shooting string” holographic jet initial configurations with finite momentum at string endpoints was proposed in arXiv:1306.6648 that suggests a more natural scheme for determining the instantaneous rate of energy loss of jets in SYM plasmas with longer stopping distances. We apply this framework to predict nuclear modification factors RAA of jets, and compare to recent data at RHIC and LHC. Phenomenological consequences of non-conformal deformations of AdS geometry and Gauss-Bonnet quadratic curvature corrections will be discussed.

Speaker: Andrej Ficnar (Columbia University)

Slides HP2013.pptx

15:10 Radiation spectrum of a massive quark-gluon antenna in a QCD medium

We derive the radiation spectrum of a massive quark-gluon antenna in a QCD medium. The calculation is done in the formalism of the classical Yang-Mills (CYM) equations and interactions with the medium are handled in the harmonic oscillator approximation, valid for soft gluon emissions. We discuss the effect produced by the presence of a mass scale and compare the results with the massless case. We put our findings in relation with the energy loss of heavy quarks in heavy ion collisions, one of the phenomenological puzzles of RHIC and LHC data.

Speaker: Mr Manoel Rodríguez Calvo (Universidade de Santiago de Compostela - IPhT CEA Saclay)

Slides Cape_Town.pdf

13:30 → 15:30 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Prof. Alexander Kovner (University of Connecticut)

13:30 Applications of JIMWLK Evolution to Exclusive J/Psi Production

The Large Hadron Collider, located at the European Centre for Nuclear Research, is the most powerful particle collider ever built. The ATLAS experiment at the LHC uses the proton and heavy ion collisions produced in this 27 km long collider to probe the predictions and limitations of the Standard Model. Due to the high energies employed, collisions are able to probe a regime known as the Colour Glass Condensate (CGC): a medium characterized by a part of the hadronic wavefunctions being dominated by nonperturbatively large gluon occupation numbers. The JIMWLK equation is a mathematical tool used to predict some of the physical observables within the CGC framework. By exploiting appropriate exclusive interactions (where at least one of the protons does not break), this work attempts to calculate the exclusive J/Psi production cross-section using a truncation of the JIMWLK equation and to measure this cross-section in the ATLAS experiment.

Speaker: Ms Andrecia Ramnath (University of Cape Town)

Slides Ramnath_HP_Talk.pdf

13:50 Predictions for the Spatial Distribution of Gluons in the Initial Nuclear State

We demonstrate measurable, falsifiable differences between the DGLAP and CGC predictions for the t-differential cross section of exclusive vector meson production (EVMP) in electron-ion collisions. These predictions permit an experimental determination of the dominant physical processes for low-x gluons in a high-energy nucleus. At eRHIC energies, J/psi photoproduction in e+A collisions provides an ideal experimental probe for the spatial distribution of gluons. EVMP grants experimental access to the edge region of the highly-boosted nuclear wavefunction, where the saturation scale for CGC calculations becomes inaccessible to pQCD. On the other hand, DGLAP evolution requires careful consideration of unitarity effects. Under these different small-x frameworks we obtain a measurable distinction in both the shape and normalization of the differential cross section predictions. An eRHIC measurement of such an EVMP cross section will therefore constrain the initial state in heavy ion collisions, allowing for a more quantitative study of the properties of the quark-gluon plasma.

Speaker: Mr Greg Jackson (University of Cape Town)

Slides GregJackson_HardProbes2013.pdf

14:10 Color Class Condensate from electron-proton DIS to proton-nucleus collisions

The Color Class Condensate offers a consistent framework to describe high-energy (small-x) data from various experiments. The non-perturbative input for these calculations, the dipole-target amplitude at initial Bjorken-x, is obtainable from electron-proton deep inelastic scattering processes. Once that is known, one can compute, for example, single and double inclusive particle production in proton-proton and proton-nucleus collisions. Proton-nucleus collisions are especially interesting as the saturation scale is expected to scale as A^1/3, making saturation phenomena easier to observe in pA than pp collisions. We discuss how tightly the electron-proton DIS data constrains the initial condition for the dipole amplitude and how the LHC single inclusive spectra can be used to further test the CGC picture. Then using only information from DIS experiments we generalize the dipole amplitude to nuclear targets and compute particle production in proton-nucleus collisions [1]. We present predictions for the nuclear suppression factor R_pA at forward rapidities and compare with pQCD calculations. We also discuss how the back-to-back structure of the forward dihadron production cross section is modified when moving from proton-proton to proton(deuteron)-nucleus collisions, as naturally understood in the CGC [2]. References: [1] T. Lappi, H. Mäntysaari, in progress [2] T. Lappi, H. Mäntysaari, Nucl. Phys. A908 (2013) 51-72

Speaker: Mr Heikki Mäntysaari (University of Jyväskylä)

Slides hp2013_mantysaari.pdf

14:30 Measuring the gluon distribution in nuclei at an Electron-Ion Collider

Despite the successes of the HERA collider, where much information was gained on the structure of the nucleon, data on the structure of the nucleus at moderate-to-small x remains elusive, as only fixed-target high-x data currently exist. The small-x region, however, is of great interest. The nucleon structure in this region is dominated by gluons which show a rapid rise with decreasing x. At low-x, this growth must be tamed and the gluon distribution will be saturated. This saturation phenomena is expected to be universal, appearing in both nucleons and nuclei. A knowledge of this regime is of vital importance to understanding the underlying physics which governs the initial conditions of heavy-ion collisions at both the LHC and RHIC, where particle production is dominated by gluons from this unknown region. However, only tantalising hints of this have been observed so far. Therefore, the construction of an Electron-Ion Collider (EIC), colliding polarised electrons with polarised protons and also a wide variety of nuclei, will allow an exploration of the region of small-x in great detail (with luminosities 100x that of HERA), answering questions on both the spatial and momentum distributions of gluons and sea quarks in nuclei. In particular, the saturation region is more accessible in nuclei due to the amplification of the saturation scale with nuclear size (Q_s ~ A^(1/3)). In this talk I will present the current status of the physics capabilities of e+A collisions at an EIC as outlined in the EIC White paper [1]. [1] A. Deshpande at al, arXiv:1212.1701, (2012)

Speaker: Dr Matthew Lamont (BNL)

Slides HardProbes2013_macl_Keynotev9.pdf

14:50 EIC: New Scientific and Technology Frontiers for Parton Femtoscopy

Our understanding of the structure of nucleons is described by the properties and dynamics of quarks and gluons in the theory of quantum chromodynamics. With advancements in theory and the development of phenomenological tools we are preparing for the next step in subnuclear tomographic imaging at a future electron-ion collider. High center-of-mass energies (up to 150 GeV) in combination with extremely high luminosities (up to 10^34 /s/cm^2) will provide the precision and a kinematic reach well into the gluon dominated regime of very low parton momenta where a saturation of the gluon density is expected, in particular in collisions of electrons with heavy nuclei. In addition, highly polarized nucleon and electron beams (70% polarization) can probe the parton polarizations in previously unexplored kinematic regions and with unprecedented accuracy, as well as address the role of orbital angular momentum with respect to the nucleon spin. This talk will summarize the theoretical, experimental and technical challenges of such a versatile experimental endeavor as planned for the Electron Ion Collider.

Speaker: Prof. William Brooks (Universidad Técnica Federico Santa María)

Slides HP2013_v4.pdf

15:10 Double parton scattering in proton-nucleus and nucleus-nucleus collisions at the LHC

Multi-parton scatterings are extremely enhanced in interactions involving nuclei at colliders, compared to proton-proton collisions at the same energy. We present the derivation of a simple generic expression to compute double-parton scattering (DPS) cross sections in high-energy proton-nucleus and nucleus-nucleus collisions as a function of the corresponding single-parton hard cross sections and of the event centrality. We apply such DPS formalism to two different final-states at CERN LHC energies: (i) same-sign W-boson pair production in p-Pb [1], and (ii) double-J/psi production in Pb-Pb [2], using NLO predictions with nuclear PDF modifications for the corresponding single-parton scatterings. The first process can help determine the effective sigma_eff parameter characterising the transverse distribution of partons in the nucleon. The second process provides interesting insights on the event-by-event enhancements and/or suppressions observed in prompt-J/psi production in Pb-Pb collisions at the LHC. Both processes are experimentally measurable and the expected event rates, after acceptance and efficiency losses, for the signal and backgrounds will be discussed. [1] D. d'Enterria and A.M. Snigirev, Phys.Lett. B718 (2013) 1395; arXiv:1211.0197. [2] D. d'Enterria and A.M. Snigirev, arXiv:1301.5845.

Speaker: David d'Enterria (CERN)

Slides dde_DPS_pA_AA_southafrica_hp13.pdf

15:30 → 16:00 Coffee Break

16:00 → 17:00 Poster Session

17:00 → 18:00 Round Table Discussion: p(d)-A Centrality Determination

18:00 → 19:10 Memorial for Bob Thews and Vesa Ruuskanen

Two members of the original Hard Probes Collaboration, the precursor for
the Hard Probes meetings

Paper from Dinesh

Slides

• HP2013_KJE.pdf
• Mangano-BobThews.pdf
• Memorial.pdf
• thews.pdf
• Vesa+bob.pdf

18:00 Video Presentation

Speaker: Prof. Helmut Satz (University of Bielefeld, Germany)

18:20 Vesa Ruuskanen

Speaker: Ramona Vogt (LLNL and UC Davis, USA)

Slides Vesa+bob.pdf

18:30 Robert Thews

Speaker: Prof. Jean Cleymans (University of Cape Town)

Slides thews.pdf

18:40 Bob, Vesa and Hard Probes

Speaker: Prof. Xin-Nian Wang (Lawrence Berkeley National Laboratory)

18:50 Johnnie Thews

Wednesday, 6 November

08:30 → 10:00 Plenary

Plenary Session

Convener: Ramona Vogt (LLNL and UC Davis, USA)

08:30 Light and heavy flavor energy loss phenomenology

Speaker: Dr Magdalena Djordjevic (Institute of Physics, University of Belgrade)

Slides 1_MDjordjevic_HP2013.ppt

09:00 ALICE Heavy Flavor Results

Speaker: Dr Davide Caffarri (Università degli Studi di Padova)

Slides DCaffarri_HP2013_ALICEHF_plenary.pdf

09:30 Quark Energy Loss in a Strongly Coupled Fluid Close To and Far From Equilibrium

Speaker: Mr Mindaugas Lekaveckas (MIT)

Slides HP_Lekaveckas.pdf

10:00 → 10:30 Coffee Break

10:30 → 12:30 Plenary

Plenary Session

Convener: Dr Barbara Jacak (Department of Physics &amp; Astronomy)

10:30 Electromagnetic Fingerprints of the Little Bang

Speaker: Prof. Ulrich Heinz (The Ohio State University)

Slides Slides (optimized pdf)

11:00 Dielectron production in Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, and 62.4 GeV from STAR

Speaker: Joey Butterworth (Rice University)

Slides HP2013_Butterworthv10.pdf

11:30 Direct-photon hadron correlations and jets in heavy-ion collisions at PHENIX

Speaker: Dr Janette Hanks (Stony Brook University)

Slides AHanks_HardProbes2013.pdf

12:00 Next-to-leading order thermal photon production in a weakly coupled quark-gluon plasma

Speaker: Dr Jacopo Ghiglieri (McGill University)

Slides 7_photon_hp2013_ghiglieri.pdf

12:30 → 18:00 Excursion

Thursday, 7 November

08:30 → 10:00 Plenary

Plenary Session

Convener: Prof. Ulrich Heinz (The Ohio State University)

08:30 Jet Correlations Theory

Speaker: Dr Thorsten Renk (University of Jyväskylä)

Slides trenk-HP.pdf

09:00 Measurements of long-range angular correlations and anisotropy in d+Au collisions at 200 GeV from PHENIX

Speaker: Dr Shengli Huang (Vanderbilt University)

Slides 2_HardProbes2013_ShengliHuang.pdf

09:30 Study of the long-range correlation in high multiplicity p+Pb collisions with the ATLAS detector

Speaker: Alexander Milov (Weizmann Institute of Science)

Slides ppb_correlations_sasha_hp2013_v2.pdf

10:00 → 10:30 Coffee Break

10:30 → 12:30 Plenary

Plenary Session

Convener: Carlos Salgado (Universidade de Santiago de Compostela)

10:30 Theoretical Overview of Initial State and Flow Physics

Speaker: Prof. Sangyong Jeon (McGill University)

Slides 4_talk_cape_town_2013_jeon.pdf

11:00 Azimuthal correlations with ALICE

Speaker: Dr Alexandru Florin Dobrin (Utrecht University)

Slides dobrin_HP13.pdf

11:30 Correlations and flow phenomena in pPb and PbPb at CMS

Speaker: Dr Wei Li (Rice University)

Slides 6_HardProbe2013-WeiLi-CorrelationPlenary-11072013v4.pdf

12:00 The Search for Gluon Saturation in pA Collisions

Speaker: Prof. Bowen Xiao (Central China Normal University)

Slides HP13_Xiao.pdf

12:30 → 13:30 Lunch

13:30 → 15:10 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Dr Peter Steinberg (Brookhaven National Laboratory)

13:30 p-Pb collisions: particle production and centrality determination in ALICE.

Proton-nucleus collisions are studied to disentangle initial state effects, already present in cold nuclear matter, from final state effects, expected only when a dense and hot medium is formed as in A-A collisions. The collisions can be characterized through the number of binary collisions the nucleons undergo. In p-Pb collisions, the low particle multiplicities and the large multiplicity fluctuations influence the way collisions are classified into different centrality classes using a particle multiplicity distribution. ALICE uses different estimators to measure event-by-event the number of collisions through a Glauber approach. ALICE results on particle production in p-Pb collisions at sqrt(s_NN) = 5.02 TeV will be presented, including the pseudo-rapidity and transverse momentum dependence. The centrality determination will be addressed and its implications will be discussed.

Speaker: Dr Chiara Oppedisano (INFN, Torino, Italy)

Slides 1_Chiara_HP2013-Oppedisano.pptx

13:50 Centrality dependence of charged particle spectra in Proton-Lead collisions at sort(s_NN) = 5.02 TeV with the ATLAS detector

To Be Completed

Speaker: Dr Martin Spousta (Charles University in Prague)

Slides 2-Spousta_HP2013_20131025.pdf

14:10 Minijet analysis in pA collisions with ALICE Experiment at LHC

At LHC energies, several pairs of partons can collide in each pp, p-A or A-A collision. Multiple Parton Interactions (MPI) can affect many physical observables, such as the charged particle multiplicity and the average transverse momentum per event. In order to include jets down to the lowest energies ("minijets"), a two-particle correlation analysis is performed with the ALICE Experiment. The correlation is expressed as associated yield per trigger particle and allows to extract the number of uncorrelated seed particles which is proportional to the number of MPI. The quantities are presented for different multiplicity estimators and in different collision systems.

Speaker: Emilia Leogrande (University of Utrecht)

Slides EL_HP_2013.pdf

14:30 Measuring cold nuclear matter effects via di-jets in pPb collisions with ALICE

We present a measurement of jet correlations in p-Pb collisions at \sqrt{s}=5.02 TeV. The aim of the measurement is to test whether cold nuclear matter effects and shadowing are present in p-Pb collisions. Jets are measured using the central detectors using the anti-kT jet algorithm. In the analysis the underlying event is subtracted event-by-event. Corrections for the remaining underlying event contribution and the finite detector resolution are applied on an inclusive basis. A measurement of the dijet k_{T} as function of the transverse momentum of the jet, varying jet resolution parameter, and the event multiplicity will be presented. This observable is a measure of the acoplanarity of dijet production which is potentially modified. In addition the correlation in pseudorapidity of jet pairs which is sensitive to nuclear shadowing will be discussed.

Speaker: Marta Verweij (Wayne State University)

Slides pPbDiJetsMVerweijV2.pdf

14:50 Spatially dependent nPDFs and their applications in inclusive pion and prompt photon production

I will focus on the nuclear PDFs (nPDFs) and their applications in high energy A+A and p/d+A collisions. First, I will introduce our recently published spatially dependent nPDF sets, EPS09s and EKS98s, and discuss the centrality dependence of hard-process cross-sections within the collinear factorization framework. More specifically, I will compare our NLO pQCD calculations for the nuclear modification factor of neutral pion and prompt photon production with the data in d+Au and Au+Au collisions at RHIC and for p+Pb and Pb+Pb collisions at the LHC at midrapidity in different centrality classes. These calculations are found to be well in line with the published data. After this, I will discuss the same observables also at forward rapidities and show to what extent these will probe the small-$x$ gluon densities in p+Pb collisions at the LHC. In addition, we have implemented the spatially dependent nPDFs into a Monte-Carlo Glauber framework to study whether the centrality dependence turns out to be different (stronger) than with the optical Glauber model used so far.

Speaker: Mr Ilkka Helenius (University of Jyväskylä)

Slides helenius_HardProbes2013.pdf

13:30 → 15:10 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Prof. Sangyong Jeon (McGill University)

13:30 Ridge correlations from initial state.

I describe several mechanisms that lead to ridge like correlations in the produced particle spectrum in p-p and p-A collisions at high energy. The discussion is within the Color Glass Condensate framework, but the physics involved is not directly tied with saturation.

Speaker: Prof. Alexander Kovner (University of Connecticut)

Slides Kovner_HP2013.pdf Lublinsky_HP2013.pdf

13:50 Long range two-particle correlations and initial state

We address the relation between the long range two-particle correlations observed at the LHC and the B-Reggeon. The latter is a four-point generalization of the BFKL Pomeron also emerging as a new element of the QCD Reggeon Field Theory.

Speaker: Dr Michael Lublinsky (Ben-Gurion University of the Negev)

Slides 2_Lublinsky_HP2013.pdf

14:10 Di-jet asymmetric momentum transported by QGP fluid

High energy partons propagating through the QGP medium are subject to deposit their energy and momentum into the medium. The dynamics of the QGP fluid would be affected by the energy-momentum deposition from these energetic partons. We study the collective flow of the QGP fluid induced by the jets using a (3+1)-dimensional QGP-fluid+Jet model. We simulate the propagation of jets together with expansion of the QGP fluid and calculate the transverse momentum distribution of the particles originated from the medium. As a result, a large fraction of the momentum imbalance of the di-jet is compensated by low-pT particles at large angles from the jet axis. This result is consistent with the one observed by the CMS Collaboration [1]. References [1]S. Chatrchyan et al. [CMS Collaboration], Phys. Rev. C 84, 024906 (2011); C. Roland, J. Phys. G 38, 124020 (2011) .

Speaker: Mr Yasuki Tachibana (The University of Tokyo)

Slides tachibana_hp2013_2.pdf

14:30 Dihadron azimuthal correlations at large pseudo-rapidity difference in multiplicity-selected d+Au collisions by STAR

A long-range pseudo-rapidity correlation is unexpectedly observed in pp and p+Pb collisions at the LHC after a uniform background subtraction. It is called the "ridge," in analogy to the similar phenomenon in heavy-ion collisions after subtraction of an elliptic-flow-modulated background. The heavy-ion ridge has been attributed primarily to triangular anisotropy, resulting from initial geometry fluctuations and subsequent hydrodynamical evolution. The question arises whether the pp/p+Pb ridge is of similar origin, which would be surprising in the small collision systems of pp and p+Pb. Another physics mechanism, the color glass condensate, is also proposed as an explanation for the correlated production of dihadrons forming the ridge. PHENIX showed, following the method by ALICE and ATLAS, that the difference of dihadron correlations between central and peripheral collisions can be mostly described by a second harmonic. While it is an open question how much jet contribution remains in the PHENIX result in their limited acceptance, the complementarity between LHC and RHIC can be potentially powerful to distinguish the proposed ridge production mechanisms. In this talk, we present STAR results of dihadron correlations in d+Au collisions as a function of multiplicity, with the large acceptance of |\Delta\eta|<2 by the STAR's Time Projection Chamber (TPC). We also present dihadron correlations using STAR's mid-rapidity TPC and forward TPC, with a |\Delta\eta| coverage of 1.8-4.8. We examine the \Delta\eta dependence of the correlations as well as the difference in the correlations between central and peripheral collisions. We discuss our results in the context of the LHC and PHENIX data.

Speaker: Prof. Fuqiang Wang (Purdue University)

Slides 4_HP2013_fqwang.pdf

14:50 Two-particle correlations in pp, p-Pb and Pb-Pb collisions measured in ALICE

Two-particle correlation studies in high-multiplicity pp and p-Pb collisions at LHC energies have revealed unexpected structures. A symmetric double-ridge correlation pattern was found in p-Pb collisions at sqrt(s_NN)=5.02 TeV that extends to large differences in pseudorapidity. This observation can be attributed to collective behavior in the initial and final state of the collision using saturation and hydrodynamic models. To further investigate these effects, two-particle azimuthal correlations have been studied for inclusive and identified charged particles in pp collisions at sqrt(s)=7TeV and p-Pb collisions at sqrt(s_NN)=5.02 TeV. The results are compared to those from Pb-Pb collisions. Saturation effects in p-Pb are expected to be enhanced in the low-x regime of the nucleus that can be probed at forward rapidities. Potential future measurements in this kinematic region are discussed.

Speaker: Tim Schuster (Yale University)

Slides Schuster_ALICE_HP2013.pdf

13:30 → 15:10 Jet Quenching and Observables

Jet Quenching and Observables

Convener: Dr Christof Roland (MIT)

13:30 A hybrid strong/weak coupling approach to jet quenching

We study the modification of jet properties in a heavy ion environement by the presence of strongly coupled quark gluon plasma. We explore a hybrid approach, in which the high virtuality splitting processes that dominate the QCD shower proceed as in vacuum while the partons of the shower interact with the system as dictated by strongly coupled computations via the AdS/CFT correspondence. We incorporate this approach into an event Monte Carlo and study multiple jet observables, such as jet suppression, di-jet asymmetry, etc. We show that this approach is in qualitative agreement with the available jet measurements at the LHC, but a quantitative description may require additional sources of energy loss, such as radiative processes.

Speaker: Mr Daniel Pablos (Universitat de Barcelona)

Slides 1PablosHP.pdf

13:50 Measurement of jet production in central Pb–Pb collisions at √sNN = 2.76 TeV using semi-inclusive hadron-jet distributions

The ALICE collaboration at the LHC presents a measurement of jet production rates recoiling back-to-back from a high pT trigger hadron. The observable is the difference between normalized recoil jet spectra for two hadron pT trigger intervals. This approach allows the removal of the large combinatorial jet background in heavy ion events in a model-independent way, while preserving collinear safety and a low infrared cutoff (150 MeV) for the coincidence recoil jet population. The jet recoil yield is measured over a wide pT range for different choices of jet cone radius. The azimuthal distribution of recoil jets is also explored. The measurements are compared to a calculation of the same observable for pp collisions using Next-to-Leading Order perturbative QCD, and to predictions of Monte Carlo models incorporating jet quenching.

Speaker: Dr Leticia Cunqueiro (CERN)

Slides HPCcunqueiro.pdf

14:10 Understanding Jet Modifications at the LHC

Jets are collimated QCD multi-particle states that are abundantly produced in heavy-ion collisions at the LHC. Their description in the vacuum is governed by hardest scale of the problem, typically the jet virtuality. In the presence of a background color field, e.g. such as expected in a quark-gluon plasma, one also has to consider a hard scale arising from the medium interactions. It was recently shown that due to the collinear nature of QCD splittings, high-energy jets are typically quite collimated and are not resolved by the medium, i.e. they are only seen as a total charge and lose energy coherently. Assuming this scenario holds for all jets, we show how a factorization of small-angle jet evolution and large-angle medium-induced emissions can be realized and calculate three key observables: the jet RAA, modification of the intra-jet structure and the amount of out-of-cone radiation. Medium-induced radiation is accounted for using the established factorization of multiple branchings leading to the probabilistic rate equation - which we presently improve upon by introducing finite-size effects and a proper regularization prescription in the infrared. This mechanism is particularly important for the transport of energy away from the jet axis up to large angles. For the intra-jet structure, on the other hand, we find the striking importance of so-called "antiangular ordered radiation," resulting from the slight decoherence of the jet during the passage through the medium.

Speaker: Dr Konrad Tywoniuk (Universitat de Barcelona)

Slides hp2013_KT.pdf

14:30 Jet quenching effects on the elliptic and triangular flow at RHIC

In this work we investigate how the energy and momentum lost by partonic jets in the quark-gluon plasma may affect the final elliptic and triangular flow of low p_T hadrons at RHIC energies. The jets are modeled as external sources in the energy-momentum conservation equations of ideal hydrodynamics, which are solved on an event by event basis. We find that the average integrated elliptic (triangular) flow and the participant eccentricity (triangularity) can become significantly less linearly correlated if the energy loss rate is sufficiently large (dE/dx > 10 GeV/fm). We show that the linear correlation between v_3(p_T < 1 GeV) and v_3(2 < p_T < 3 GeV) is particularly sensitive to the magnitude of dE/dx and, thus, this new observable may be used to distinguish between strong and weak coupling scenarios for the jet energy loss in the QGP.

Speaker: Dr Rone Andrade (Universidade de São Paulo)

Slides rone_andrade.pdf

14:50 Inclusive jet production in p+Pb collisions at 5.02 TeV with the ATLAS detector at the LHC jet quenching

Measurements of reconstructed jets in high-energy proton-lead collisions over a wide rapidity and pT range can shed light on the partonic structure of nuclei. Inclusive jet production is sensitive to the nuclear modification of parton distribution functions and, in the forward direction and at small transverse momenta, can provide constraints on the saturation of low Bjorken-x partons in the high-density Pb nucleus. Furthermore, any modification of jet production in p+Pb collisions requires that the strong suppression seen in central Pb+Pb collisions be understood in the light of these nuclear effects. We present the latest results on inclusive jet production in p+Pb collisions at 5.02 TeV measured in the new high statistics 2013 data with the ATLAS detector at the LHC.

Speaker: Mr Dennis Perepelitsa (Columbia University)

Slides 5dvp-HardProbes13-11-07-13.pdf

15:10 → 15:40 Coffee Break

15:40 → 17:00 Hard and Thermal Electroweak Probes

Hard and Thermal Electroweak Probes

Convener: Prof. Itzhak Tserruya (Weizmann Institute)

15:40 Isolated photon measurements in pp and PbPb collisions with CMS

We report new measurements using isolated photons based on the high statistics 2.76 TeV pp reference data collected in 2013. The nuclear modification factors of reconstructed isolated photons, obtained by the comparison of heavy ion collisions and pp data, are presented and provide useful constraints to the nuclear parton distribution functions. For events containing an high pT isolated photon with an associated jet, the photon+jet pT imbalance is studied as a function of collision centrality and compared to pp data and model calculations. These measurements allow an unbiased characterization of the in-medium parton energy loss.

Speaker: Mr Richard Barbieri (Massachusetts Institute of Technology)

Slides 2013-10-27-HardProbesPhotons-alex_v6.pdf

16:00 Medium Modification of γ-jets in High-energy Heavy-ion Collisions

Jet propagation within a strongly coupled medium is described with a Linearized Boltzmann Transport model. In this talk, I will explain two puzzling features in the experimental study of jet quenching in central Pb+Pb collisions at LHC with the LBT model. A γ-tagged jet is found to lose about 15% of its initial energy while its azimuthal angle remains almost unchanged due to rapid cooling of the medium. The reconstructed jet fragmentation function remains almost the same as in vacuum with enhancement at large momentum fraction because of the increased contribution of leading particles to the reconstructed jet energy. A γ-tagged jet fragmentation function is proposed that is more sensitive to jet-medium interaction and jet transport parameter in the medium. Effects of recoiled medium partons on the reconstructed jets are also discussed.

Speaker: Yan Zhu (University of Santiago de Compostela)

Slides HP13_YZ.pdf

16:20 Boson production in lead-lead collisions in the ATLAS experiment

Lead-lead collisions at the LHC have are capable of producing a system of deconfined quarks and gluons at unprecedented energy density and temperature. Partonic-level interactions and energy-loss mechanisms in the medium can be studied with the aid electroweak bosons which carry an important information about the properties of the medium. Electroweak bosons form a class of unique high-pT probes because they or their decay products do not interact with the strongly-coupled medium, providing a benchmark for a variety of other phenomena measured with strongly interacting particles. The ATLAS experiment measures isolated high-pT photons, W and Z bosons via different decay channels. New analysis of experimental data obtained at the LHC with lead-lead beams at sqrt(s_NN) = 2.76 TeV. This talk will present a comprehensive study of the scaling properties of electroweak bosons showing linear proportionality of production rates to the nuclear thickness function; rapidity distributions W-decays directly sensitivity to nuclear parton distribution functions; latest results on the photon- and Z-boson correlations with jets.

Speaker: Thomas Balestri (Stony Brook University - ATLAS)

Slides 3-EWBosonHardProbes2013_ThomasBalestri_11_07_2013.pdf

16:40 Production of W and Z bosons in heavy-ion collisions with CMS

The Compact Muon Solenoid (CMS) is fully equipped to measure leptonic decays of electroweak probes in the high multiplicity environment of nucleus-nucleus collisions. Electroweak boson production is an important benchmark process at hadron colliders. Precise measurements of W and Z production in heavy-ion collisions can help to constrain nuclear PDFs as well as serve as a standard candle of the initial state in PbPb collisions at the LHC energies. The inclusive and differential measurements of the Z boson yield in the muon decay channel will be presented, establishing that no modification is observed with respect to next-to-leading order pQCD calculations, scaled by the number of incoherent nucleon-nucleon collisions. Measurements of the yield of W bosons decaying into a muon and an (anti)neutrino as a function of centrality, and the W charge asymmetry as a function of rapidity show no modifications beyond the expected effect of isospin when compared to pp collisions and the status of the corresponding analyses on pPb collisions will be given.

Speaker: Mrs Alice FLORENT (LLR)

Slides HP2013_Florent.pdf

15:40 → 17:00 Heavy Flavor Production and Quarkonia

Heavy Flavor Production and Quarkonia

Convener: Dr Anthony Frawley (Forida State University)

15:40 Quarkonium production and polarization in pp collisions with the CMS detector

Studies of the production of heavy quarkonium states are very important to improve our understanding of QCD and hadron formation, given that the heavy quark masses allow the application of theoretical tools less sensitive to nonperturbative effects. Thanks to a dedicated dimuon trigger strategy, combined with the record-level energy and luminosity provided by the LHC, the CMS experiment could collect large samples of pp collisions at 7 and 8 TeV, including quarkonium states decaying in the dimuon channel. This allowed the CMS collaboration to perform a series of systematic measurements in quarkonium production physics, including double-differential cross sections and polarizations, as a function of rapidity and pT, for five S-wave quarkonia: J/psi, psi(2S), Y(1S), Y(2S), and Y(3S). Some of these measurements extend well above pT~50 GeV, probing regions of very high pT/mass, where the theory calculations are supposed to be the most reliable. Thanks to its high-granularity silicon tracker, CMS can reconstruct low-energy photons through their conversions to e+e- pairs, thereby accessing the radiative decays of the P-wave quarkonium states, with an extremely good mass resolution, so that the J=1 and J=2 1P states can be resolved. This allows CMS to determine cross-section ratios and feed-down decay fractions involving the chi states, in both the charmonium and bottomonium families. Such measurements provide crucial inputs to a better understanding of quarkonium production as a signal of new physics in Pb-Pb collisions. This talk presents the CMS quarkonium production results, in pp collisions, placing emphasis on the most recent measurements, which include the polarizations of all five S-wave states, the most comprehensive measurement of quarkonium polarization made so far. We will also present brand-new results on P-wave quarkonium production in the bottomonium family. It is likely that other preliminary results on quarkonium production in pp collisions, of particular relevance for the understanding of heavy-ion measurements, will be shown at this conference for the first time.

Speaker: Mr Valentin Knuenz (Institute of High Energy Physics, Vienna, Austria)

Slides 1-CMS-pp-onia-HP2013-final.pptx CMS-pp-onia-HP2013-final.pdf

16:00 Quarkonium production and polarization, from elementary to Pb-Pb collisions

Non-relativistic QCD (NRQCD) is commonly expected to describe the production of heavy quarkonium states in elementary collisions. It has been claimed to provide good descriptions of differential production cross sections of several quarkonia, while failing to reproduce the polarization measurements, a problem often attributed to the unreliability of the measurements. In this presentation we show how the very recent LHC measurements, both cross sections and polarizations, compare to NRQCD. We show that different NLO NRQCD approaches lead to seemingly contradictory conclusions and we offer some thoughts regarding what this surprising observation tells about the validity of the NRQCD framework and about quarkonium production. In particular, we explore the possibility that the long-distance matrix elements (LDMEs) describing the transitions from the colour octet states to the observable states, crucial non-perturbative ingredients of the calculations, might not be universal. In that case, the NRQCD framework remains valid, but hadroproduction and photoproduction data are not described by the same set of matrix elements. This observation, while not being as surprising as one might tend to think at first, triggers intriguing questions on the importance of the surrounding hadronic environment in the production of quarkonium states, already in elementary collisions. This discussion shows that it is not unreasonable to expect different LDMEs in pp and PbPb collisions, where the abundance of gluons may favour otherwise suppressed transitions. Studies of quarkonium production in heavy-ion collisions, to probe QGP melting and/or recombination effects, are therefore remarkably intertwined with the ("cold") nuclear modifications of the LDMEs. We conjecture that accurate results on J/psi and Upsilon(1S) polarizations in Pb-Pb collisions, easily obtainable at the LHC, could provide unique measurements of the long-sought P-wave suppression patterns, thereby reliably probing sequential quarkonium melting, a signature of deconfinement mostly insensitive to "cold nuclear matter" effects. We finish by proposing measurements of the polarizations of quarkonia in ultra-peripheral Pb-Pb collisions, as a way to study quarkonium production in still another environment, dominated by gamma-gamma interactions instead of gluon-gluon interactions. Such data could provide a clear-cut challenge to LDME universality.

Speaker: Dr Carlos Lourenco (CERN)

Slides 2-CL-HP13-final.pptx

16:20 Inclusive J/ψ and ψ(2S) production in p-Pb collisions at √sNN = 5.02 TeV with ALICE at the LHC

Charmonia are considered as a key observable for deconfinement in nucleus- nucleus (A-A) collisions at LHC energies. Measurements in proton-nucleus (p-A) collisions provide important information to investigate nuclear effects, which are commonly not attributed to the Quark-Gluon Plasma. In ALICE, J/ψ production has been measured in proton-proton, p-A and A-A collisions down to pT = 0 GeV/c both via their dimuon decay in the forward muon spectrometer and with dielectrons in the central barrel. √ In this talk, results on the J/ψ nuclear modification factor RpA at sNN = 5.02 TeV as a function of rapidity, covering the forward (2.03 < ycms < 3.53), central (-1.37 < ycms < 0.46) and backward range (-4.46 < ycms < -2.96), will be presented as well as RpA(pT ). Results on ψ(2S) at forward and backward rapidity will also be discussed. Finally, comparisons with theoretical models will be carried out.

Speaker: Mr Michael Winn (University of Heidelberg)

Slides 3_MWinn_HP2013_JPSI_pA_v4.pdf

15:40 → 17:00 Initial State and Proton-Nucleus Collision Phenomena

Initial State and Proton-Nucleus Collision Phenomena

Convener: Dr Jorge Casalderrey-Solana (Universitat de Barcelona)

15:40 Dynamics of strongly interacting parton-hadron matter

We study the the non-equilibrium dynamics of heavy-ion collisions from SIS to LHC energies within the Parton-Hadron-String Dynamics (PHSD) transport approach, which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We investigate also the equilibrium properties of strongly-interacting infinite parton-hadron matter: the equilibration of different observables on light and strange sector and their fluctuations and also transport coefficients, such as shear and bulk viscosity, electric and heat conductivity are presented.

Speaker: Prof. Wolfgang Cassing (Uni. Giessen)

Slides 6-Stellenbosh-Cassing.pdf

16:00 Elliptic Flow from Non-equilibrium Initial Condition with a Saturation Scale

A current goal of relativistic heavy ion collisions experiments is the search for a Color Glass Condensate (CGC) as the limiting state of QCD matter at very high density. In viscous hydrodynamics simulations, a standard Glauber initial condition leads to estimate 4πη/s ∼ 1, while employing the Kharzeev-Levin-Nardi (KLN) modeling of the glasma leads to at least a factor of 2 larger η/s. Within a kinetic theory approach based on a relativistic Boltzmann-like transport simulation, our main result is that the out-of-equilibrium initial distribution reduces the efficiency in building-up the elliptic flow. At RHIC energy we find the available data on v2 are in agreement with a 4πη/s ∼ 1 also for KLN initial conditions. More generally, our study shows that the initial non-equilibrium in p-space can have a significant impact on the build-up of anisotropic flow.

Speaker: Dr Francesco Scardina (University of Catania (INFN-LNS))

Slides 7-scardina.pdf

16:20 Multiplicities, p_T spectra and v_2 in A+A collisions at LHC and RHIC from NLO-improved pQCD + saturation + hydrodynamics model

We report the results from the recent studies [1,2], where we have brought the EKRT framework [3] to next-to-leading order (NLO) in pQCD, and shown the viability of the model in describing the produced initial QGP energy densities at the LHC and RHIC. Our updated framework [1] combines a rigorous NLO pQCD computation of the minijet transverse energy production with the saturation of gluons and fluid dynamics. Latest knowledge of NLO nuclear parton distributions (nPDFs) is utilized. Identifying the key parameters and charting the uncertainties of the model, we obtain an encouragingly good agreement with the charged-particle multiplicities and identified bulk hadron p_T spectra measured in 5% most central Au+Au collisions at RHIC and Pb+Pb at the LHC [1]. To obtain the initial QGP energy-density profiles dynamically in non-central collisions [2], we supplement the calculation by a local saturation condition and impact-parameter dependent nPDFs (EPS09s [4]). We address the main uncertainties associated with the obtained initial states. Using viscous fluid dynamics, we show that a good simultaneous description of the centrality dependence of multiplicity, p_T spectra and elliptic flow is obtained both at the LHC and RHIC. Ref. [1] R. Paatelainen, K.J. Eskola, H. Holopainen and K. Tuominen Phys. Rev. C87 (2012) 044904. Ref. [2] R. Paatelainen, K.J. Eskola, and H. Niemi, work in progress. Ref. [3] K.J. Eskola, K. Kajantie, P.V. Ruuskanen, K. Tuominen, Nuc. Phys. B570 (2000) 379. Ref. [4] I. Helenius, K.J. Eskola, H. Honkanen and C.A. Salgado, JHEP 1207 (2012) 073.

Speaker: Mr Risto Paatelainen (University of Jyväskylä)

Slides paatelainen_hp2013.pdf

16:40 Predictions for p+Pb Collisions at sqrt(s_NN) = 5 TeV: Expectations vs. Data

Recently a compilation of predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge boson production in p+Pb collisions at sqrt(s_NN) = 5 TeV was made available [1]. Here the predictions are compared to the data so far available. [1] J. Albacete et al., Int. J. Mod. Phys. E22 (2013) 133007.

Speaker: Ramona Vogt (LLNL and UC Davis, USA)

Slides hp13.pdf

17:30 → 22:00 Conference Dinner: Buses leave from STIAS

Friday, 8 November

08:30 → 10:00 Plenary

Plenary Session

Convener: Prof. John Harris (Yale University)

08:30 Hard Probes Lattice Theory

Speaker: Prof. Heng-Tong DING (Central China Normal University)

Slides HTD_HP2013.pdf

09:00 Quarkonia results from the PHENIX experiment

Speaker: Darren McGlinchey (University of Colorado)

Slides dmcglinchey_quarkonia_HP2013.pdf

09:30 Quarkonium measurements in the STAR experiment

Speaker: Dr Jaroslav Bielcik (FNSPE, Czech Technical University)

Slides BielcikHP2013_v3.pdf

10:00 → 10:30 Coffee Break

10:30 → 12:30 Plenary

Plenary Session

Convener: Dr Carlos Lourenco (CERN)

10:30 Quarkonia Theory

Speaker: Prof. Agnes Mocsy (Pratt Institute)

Slides Mocsy_Plenary_HP13_SA_Final.pdf

11:00 Onia production in pA and Ap collisions at LHCb

Speaker: Dr Richard Jacobsson (CERN)

Slides HardProbes2013_Jacobsson_slides.pdf

11:30 Quarkonium production in ALICE at the LHC

Speaker: Dr Cynthia Hadjidakis (CNRS)

Slides HardProbes2013-Cynthia.pdf

12:00 Charmonium and bottomonium production in heavy-ion collisions with CMS

Speaker: Dr Lamia Benhabib (CERN)

Slides HardProbes2013_LamiaBenhabib.pdf

12:30 → 13:30 Lunch

13:30 → 15:40 Plenary

Plenary Session

Convener: Prof. Charles Gale (McGill University)

13:30 Experimental Wrap-Up: Energy Loss

Speaker: Prof. Yen-Jie Lee (Massachusetts Institute of Technology)

Slides 20131108-HP2013_yenjie-v6.pdf

13:50 Experimental Wrap-Up: p(d)A - Jets and Correlations

Speaker: Prof. Brian Cole (Columbia University)

Slides pPb_summary_ridgeJet.pdf

14:10 Andreas: Experimental Wrap-Up: p(d)A - Particle Production and Nuclear Modification Factors

Speaker: Dr Andreas Morsch (CERN)

Slides HardProbes2013_WrapUp.pdf

14:30 Experimental Wrap-Up: Onia, Thermal and Electroweak Probes

Speaker: Torsten Dahms (TU München)

Slides tdahms_20131108.pdf

14:50 Theory Wrap-Up

Speaker: Dr Francois Gelis (IPhT, CEA-Saclay)

Slides FGelis-HP2013.pdf

15:30 Closing