Multiplicity Distributions In Heavy-ion Collisions Research Articles

Seventh and eighth-order cumulants of net-proton multiplicity distributions in heavy-ion collisions at RHIC-STAR

We report the first measurements of seventh and eighth-order cumulants of net-proton distributions in Au+Au collisions at √SNN=27,54.4, and 200 GeV. The measurements are performed at mid-rapidity |y| < 0.5 within 0.4 < pT < 2.0 GeV/c using the Time Projection Chamber and Time-of-Flight detector. Motivation for the measurements comes from lattice-QCD and QCD based model calculations that predict their negative signs for a crossover quark-hadron transition. While 0-40% centrality measurements at √SNN=54.4 and 200 GeV are consistent with zero within large uncertainties, at √SNN=27 GeV, they are negative with ≤ 1.4σ significance. The peripheral 70-80% measurements are either positive or consistent with zero for the three energies.

QCD Critical Point and High Baryon Density Matter

We report the latest results on the search for the QCD critical point in the QCD phase diagram through high energy heavy-ion collisions. The measurements discussed are based on the higher moments of the net-proton multiplicity distributions in heavy-ion collisions. A non-monotonic variation in the product of kurtosis times the variance of the net-proton distribution is observed as a function of the collision energy with 3$\sigma$ significance. We also discuss the results of the thermal model in explaining the measured particle yield ratios in heavy-ion collisions and comparison of the different variants of hardon resonance gas model calculation to the data on higher moments of net-proton distributions. We end with a note that the upcoming programs in high baryon density regime at various experimental facilities will complete the search for the QCD critical point through heavy-ion collisions.

Volume fluctuation and auto-correlation effects in the moment analysis of net-proton multiplicity distributions in heavy-ion collisions

Moments (variance (σ2), skewness (S), kurtosis (κ)) of multiplicity distributions of conserved quantities, such as net-baryon, net-charge and net-strangeness, are predicted to be sensitive to the correlation length of the system and connected to the thermodynamic susceptibilities computed in the Lattice QCD and Hadron Resonance Gas model. In this paper, we present several measurement artifacts that could lead to volume fluctuation and auto-correlation effects in the moment analysis of net-proton multiplicity distributions in heavy-ion collisions using the ultra-relativistic quantum molecular dynamics model. We discuss methods to overcome these artifacts so that the extracted moments can be used to obtain physical conclusions. In addition, we present methods to properly estimate the statistical errors in moment analysis.