Centrality determination with a forward detector in the RHIC Beam Energy Scan

TL;DR

This paper demonstrates that a refined forward rapidity particle multiplicity measure significantly improves impact parameter resolution in RHIC Beam Energy Scan experiments, aiding the search for the QCD critical point.

Contribution

It introduces an improved centrality measure based on forward rapidity particles, enhancing impact parameter resolution in heavy ion collision experiments.

Findings

Enhanced impact parameter resolution with the new measure

Improved performance even after detector simulation filtering

Highlights importance for critical point search in QCD phase diagram

Abstract

Recently, Chatterjee et al used a hadronic transport model to estimate the resolution with which various experimental quantities select the impact parameter of relativistic heavy ion collisions at collision energies relevant to the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Measures based on particle multiplicity at forward rapidity were found to be significantly worse than those based on midrapidity multiplicity. Using the same model, we show that a slightly more sophisticated measure greatly improves the resolution based on forward rapidity particles; this improvement persists even when the model is filtered through a realistic simulation of a recent upgrade detector to the STAR experiment. These results highlight the importance of optimizing centrality measures based on particles detected at forward rapidity, especially for experimental studies that search for a critical point in the QCD phase diagram. Such measurements usually focus on proton multiplicity fluctuations at midrapidity, hence selecting events based on multiplicity at midrapidity raises the possibility of nontrivial autocorrelations.