Event-by-Event Identified Particle Ratio Fluctuations in Pb-Pb Collisions with ALICE using the Identity Method

TL;DR

This paper investigates event-by-event fluctuations of identified particle ratios in Pb-Pb collisions at the LHC using the ALICE detector, employing a novel 'Identity Method' to improve particle identification accuracy.

Contribution

The paper introduces the application of the 'Identity Method' for analyzing particle ratio fluctuations in heavy-ion collisions, providing new insights into the underlying dynamics.

Findings

Peripheral collisions show increased pion-proton correlations not matched by models.

Central collisions' fluctuations align with lower-energy data extrapolations.

First application of the 'Identity Method' in this context.

Abstract

The study of event-by-event fluctuations of identified hadrons may reveal the degrees of freedom of the strongly interacting matter created in heavy-ion collisions and the underlying dynamics of the system. The observable $\nu_{dyn}$, which is defined in terms of the moments of identified-particle multiplicity distributions, is used to quantify the magnitude of the dynamical fluctuations in event-by-event measurements of particle ratios. The ALICE detector at the LHC is well-suited for the study of $\nu_{dyn}$, due to its excellent particle identification capabilities. Particle identification based on the measurement of the specific ionisation energy loss, d$E$/d$x$, works well on a statistical basis but suffers from ambiguities when applied on an event-by-event level. A novel experimental technique called the "Identity Method" is used to overcome such limitations. The first results on identified particle ratio fluctuations in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76TeV in ALICE as a function of centrality are presented. The ALICE results for the most peripheral events indicate an increasing correlation between pions and protons which is not reproduced by the HIJING and AMPT models. On the other hand, for the most central events the ALICE results agree with the extrapolations based on the data at lower energies from CERN-SPS and RHIC.