Measuring the speed of sound using cumulants of baryon number

TL;DR

This paper demonstrates how cumulants of baryon number distributions can be used to determine the speed of sound in nuclear matter, with applications to heavy-ion collision experiments and considerations of experimental challenges.

Contribution

It introduces a method to extract the speed of sound from baryon number cumulants and discusses practical challenges in applying this to experimental data.

Findings

First three cumulants can determine the speed of sound.

Finite particle number effects influence fluctuation measurements.

Baryon number conservation impacts cumulant-based calculations.

Abstract

We show that the values of the first three cumulants of the baryon number distribution can be used to calculate the isothermal speed of sound and its logarithmic derivative with respect to the baryon number density. We discuss applications of this result to heavy-ion collision experiments and address possible challenges, including effects due to baryon number conservation, differences between proton and baryon cumulants, and the influence of finite number statistics on fluctuation observables in both experiment and hadronic transport simulations. In particular, we investigate the relation between quantities calculated in infinite, continuous matter and observables obtained in simulations using a finite number of particles.