Assessing critical point signatures through proton intermittency in NA61/SHINE

Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342, Kraków, Poland

^* e-mail: nikolaos.davis@ifj.edu.pl
^** for the NA61/SHINE Collaboration

Published online: 1 March 2023

Abstract

The search for experimental signatures of the critical point (CP) of strongly interacting matter is one of the main objectives of the NA61/SHINE experiment at CERN SPS. One such candidate observable is local fluctuations of the proton density in transverse space, constituting an order parameter of the chiral phase transition, and expected to scale according to a universal powerlaw in the vicinity of the CP. Its scaling can be probed through an intermittency analysis of the proton second scaled factorial moments (SSFMs) in transverse momentum space. The first such analysis [1] revealed power-law behavior in NA49 Si+Si collisions at 158A GeV/c, with a fitted exponent value consistent with the critical prediction, within errors.

In the present work, we discuss known challenges posed by standard intermittency analysis in the face of low to moderate event statistics, and propose a novel technique that solves them. We perform a scan of Monte Carlo models simulating alternative critical and background scenarios, and weigh them against experimental results; we explore the method’s efficacy on simulated data. Once adapted to the available NA61/SHINE systems, the method will allow us to obtain reliable confidence intervals for the intermittency index (power-law ex-ponent) ϕ₂ compatible with the experimental data.