Speaker
Prof.
Fuqiang Wang
(Purdue University)
Description
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.
Primary author
Prof.
Fuqiang Wang
(Purdue University)
