Evaluation of Photon and Neutral Meson Measurement Capabilities Using the Upgraded PHOS Spectrometer of the ALICE Experiment

Abstract

The ALICE experiment is optimized to study the properties of hot quark-gluon plasma produced in ultra-relativistic heavy-ion collisions. One of the ALICE electromagnetic calorimeters, the Photon Spectrometer (PHOS), is designed to measure direct photons and neutral mesons spectra. At the present time the possibility of increasing acceptance of the PHOS detector by using PbWO₄ crystals of the CMS experiment is being considered. It is possible to change the kinematic range by varying pseudorapidity, with a constant azimuthal angle, or azimuthal angle, with the same pseudorapidity. It is also possible to move apart the detector modules without adding extra crystals. The simulation of proton-proton collisions at 13 TeV was carried out using the PYTHIA package. It can be argued from the obtained simulation results that for measurements in the low p_T region, the most optimal option is to increase the azimuthal angle, since it becomes possible to study the p_T region down to 25 MeV/c for π⁰. This makes it possible to measure direct photons at very low energies (tens of megaelectronvolts) and possibly to verify the Low theorem for soft photons. The available range for measuring η-meson significantly increases as well (down to 50 MeV/c).