Speaker
Description
The study of photo-nuclear reactions is crucial for understanding nuclear structure and astrophysical processes. The PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project aims to systematically investigate these reactions in nuclei with mass numbers below 60. We will use virtual photon exchange through proton scattering and high-intensity real-photon beams from laser Compton scattering to excite target nuclei. The subsequent decay particles and gamma-rays will be detected to measure photo-absorption cross-sections and decay branching ratios, covering the giant dipole resonance.
Several nuclear models, including anti-symmetrized molecular dynamics, mean-field type models, large-scale shell model, and ab initio models, will be employed to predict the systematic behavior of photo-nuclear reactions. The primary objective of the PANDORA project is to elucidate the energy-loss and mass-loss mechanisms of ultra-high-energy cosmic ray (UHECR) nuclei during intergalactic propagation.
UHECRs, observed on Earth up to energies above 10^20 eV by large cosmic-ray air-shower observatories such as Pierre Auger and Telescope Array, remain a mystery in terms of origin, acceleration mechanisms, and composition. Recent analyses suggest a heavier mass composition for UHECRs at the highest energies. UHECR nuclei are predicted to lose energy primarily by emitting particles following photo-nuclear excitation by cosmic microwave background photons. Thus, understanding photoabsorption cross-sections and decay branching ratios is essential for interpreting the energy and mass evolution of UHECRs.
I will introduce the overall project, the experimental methods for studying the photo-nuclear reactions by proton scattering at the Research Center for Nuclear Physics, Osaka University, and report on the status of the experimental results at RCNP. The contents will be optimized depending on the presentations by the other collaborators in the conference.
