Revealing baryon number fluctuations from proton number fluctuations in relativistic heavy ion collisions

TL;DR

This paper presents a method to infer baryon number fluctuations from proton number fluctuations in heavy ion collisions, accounting for isospin effects, enabling better diagnosis of the collision's early stages.

Contribution

It introduces formulas that relate baryon number cumulants to proton number fluctuations, considering the binomial isospin distribution at kinetic freezeout.

Findings

Baryon number cumulants can be expressed in terms of proton fluctuations.

Isospin distribution at freezeout is binomial and factorized.

New formulas enable direct experimental access to baryon fluctuations.

Abstract

Baryon number cumulants are invaluable tools to diagnose the primordial stage of heavy ion collisions if they can be measured. In experiments, however, proton number cumulants have been measured as substitutes. In fact, proton number fluctuations are further modified in the hadron phase and different from those of baryon number. We show that the isospin distribution of nucleons at kinetic freezeout is binomial and factorized. This leads to formulas that express the baryon number cumulants sorely in terms of proron number fluctuations, which are experimentally observable.