Closing in on critical net-baryon fluctuations at LHC energies: cumulants up to third order in Pb-Pb Collisions with ALICE

<!--HTML--><div> <p><span>Phase transitions in strongly interacting matter can be studied by investigating the response of the system to external perturbations through measurements of fluctuations and long-range correlations. In particular, fluctuations of conserved charges such as electric charge, strangeness, and baryon number can provide information on critical behaviour near the phase boundary between quark-gluon plasma and hadronic matter. Moreover, they can be compared with the generalized susceptibilities calculated in lattice quantum chromodynamics (LQCD).&nbsp;</span></p> <p><span>The ALICE collaboration presents the first experimental results on the third-order cumulants of the net-proton (proxy to net-baryon) distributions in Pb-Pb collisions at a centre-of-mass energy 5.02 TeV recorded by the ALICE detector. The results on the second-order cumulants at 2.76 and 5.02 TeV are also discussed in view of effects due to global and local baryon number conservation. The results demonstrate the presence of long-range rapidity correlations between protons and antiprotons. Such correlations originate from the early phase of the collision. The measured third-order cumulants are consistent with zero within experimental uncertainties of about 4% and are well described by the LQCD and the hadron resonance gas (HRG) model predictions. This is also a confirmation that the baryo-chemical potential (</span><span>𝜇</span><span>B</span><span>) is very close to zero at LHC energies.&nbsp;</span></p> <p><span>The completely new net-charm fluctuations as well as the 4th and higher order cumulants of net proton distributions, for which the LQCD calculations predict a significant deviation from the HRG model calculations, are also discussed in view of the operation of the LHC with increased Pb-Pb luminosity starting in 2022 and the future heavy-ion detector ALICE 3 planned for the early 2030s. </span></p> <p>ALICE Collaboration, arXiv:2206.03343</p> </div>