Determination of geometry of heavy ion collisions with forward hadron calorimeter (FHCal) at MPD/NICA

The main purpose of the FHCal is to provide an experimental measurement of a heavy-ion collision centrality (impact parameter) and orientation of its reaction plane. FHCal consists of two identical arms placed at the left/right sides from the beam collision point. Due to the fine modular structure and detection of spectators in both forward/backward regions, the angular resolution of the reaction plane reconstruction is below 30 degrees. Since the heavy fragments escape into beam holes, it is not possible to distinguish the central and peripheral collisions using only the deposited energies in FHCal. The subdivision of the calorimeter into two, inner and outer parts, and the calculation of the energy depositions separately in these calorimeter parts allow one to construct a new observable, the energy asymmetry. Taking the two-dimensional correlation between the energy asymmetry and full energy deposition in the calorimeter, it would be possible to resolve the ambiguity in the centrality determination.

New forward hadron calorimeter for centrality and reaction plane determination at BM@N heavy ion experiments

It is proposed to replace existing Zero Degree Calorimeter of the BM@N setup at the Nuclotron (JINR) by a new forward hadron calorimeter for the measurement of the collision centrality and reaction plane orientation in heavy ions experiments. This calorimeter with transverse and longitudinal segmentation will be assembled from modules presently constructed for FHCal MPD and PSD CBM. The proposed design of the new calorimeter, simulation results for centrality and reaction plane determination by the new calorimeter, as well as radiation doses in the calorimeter simulated by FLUKA are discussed. The performance of hadron calorimeter supermodule studied at CERN is shown.

The Construction and Parameters of Forward Hadron Calorimeter (FHCAL) at MPD/NICA

Forward hadron calorimeter (FHCAL) at MPD/NICA experimental setup is intended for the measurements of the geometry of heavy ions collisions, namely, the collision centrality and the orientation of the reaction plane. FHCAL consists of two identical arms placed at the left/right sides from the beam collision point. This is a modular lead- scintillator compensating calorimeter designed to measure the energy distribution of the projectile nuclei fragments (spectators) and forward going particles close to the beam rapidity.

DEPENDENCE OF ASYMMETRIES FOR CHARGE DISTRIBUTION WITH RESPECT TO THE REACTION PLANE ON INITIAL ENERGY IN HEAVY-ION COLLISIONS

In this paper, two combinations of correlators are defined in order to investigate the evolution of possible [Formula: see text] invariance violation in strong interactions with initial energy for heavy-ion collisions. These combinations correspond to absolute and relative asymmetry of distribution of electrically charge particles with respect to the reaction plane in heavy-ion collisions. Energy dependence of parameters under study was derived from data of STAR and ALICE experiments. Significant decreasing both absolute and relative asymmetry is observed at energies [Formula: see text]. This feature agrees qualitatively with other results of stage-I beam energy scan program in STAR experiment. General behavior of dependence of absolute asymmetry on initial energy agrees reasonably with behavior of similar dependence of Chern–Simons diffusion rate calculated at different values of external Abelian magnetic field. The observed behavior of parameters under study versus energy can be considered as indication on possible transition to predominance of hadronic states over quark–gluon degrees of freedom in the mixed phase created in heavy-ion collisions at intermediate energies.