Estimation of Stopped Protons at Energies Relevant for a Beam Energy Scan at the BNL Relativistic Heavy-Ion Collider

摘要

The recent net-proton fluctuation results of the STAR (Solenoidal Tracker AtRHIC) experiment from beam energy scan (BES) program at the BNL RelativisticHeavy Ion Collider (RHIC) have drawn much attention to exploring the QCDcritical point and the nature of deconfinement phase transition. There has beenmuch speculation that the non-monotonic behavior of $\kappa\sigma^{2}$ of theproduced protons around $\sqrt{s_{\rm NN}}$ = 19.6 GeV in the STAR results maybe due to the existence of QCD critical point. However, the experimentallymeasured proton distributions contain protons from heavy resonance decays, frombaryon stopping and from direct production processes. These protondistributions are used to estimate the net-proton number fluctuation. Becauseit is difficult to disentangle the protons from the above-mentioned sources, itis better to devise a method which will account for the directly producedbaryons (protons) to study the dynamical fluctuation at differentcenter-of-mass energies. This is because, it is assumed that any associatedcriticality in the system could affect the particle production mechanism andhence the dynamical fluctuation in various conserved numbers. In the presentwork, we demonstrate a method to estimate the number of stopped protons at RHICBES energies for central $0-5\%$ \auau collisions within STAR acceptance anddiscuss its implications on the net-proton fluctuation results.