Global baryon number conservation encoded in net-proton fluctuations measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

TL;DR

This paper reports on net-proton fluctuation measurements in Pb-Pb collisions at the LHC, aiming to test lattice QCD predictions for critical behavior near the QCD phase boundary, while accounting for baryon number conservation effects.

Contribution

It demonstrates for the first time that baryon number conservation causes long-range correlations affecting fluctuation measurements in heavy-ion collisions.

Findings

Baryon number conservation induces long-range correlations.

Event-by-event net-proton fluctuations are influenced by early collision interactions.

Results provide insights for interpreting fluctuation measurements in QCD phase studies.

Abstract

Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.