Cumulants: It's More Than You Think

TL;DR

This paper demonstrates that baryon number cumulants can reveal the isothermal speed of sound in nuclear matter, offering a new approach to study QCD critical point signatures and neutron star properties across various collision energies.

Contribution

It introduces a novel method to extract the isothermal speed of sound from baryon number cumulants, extending their utility beyond critical point signatures.

Findings

Lowest three cumulants relate to the speed of sound.

Method applicable across different collision energies.

Potential impact on neutron star and QCD studies.

Abstract

Cumulants of baryon number are given considerable attention in analyses of heavy-ion collision experiments as possible signatures of the QCD critical point. In this work, we show that the values of the lowest three cumulants can also be utilized to recover information about the isothermal speed of sound and its logarithmic derivative with respect to the baryon number density. This result provides a new method for obtaining information about fundamental properties of nuclear matter studied in heavy-ion collisions, with consequences for both the search for the QCD critical point and neutron star studies. While the approximations and the model comparison we considered apply to experiments at low energies, the approach itself can be used at any collision energy provided that measurements of cumulants of baryon number distribution as well as their temperature dependence are available.