Net-proton number fluctuations in the presence of the QCD critical point

Abstract

Event-by-event fluctuations of the net-proton number studied in heavy-ion collisions provide an important means in the search for the conjectured critical end point (CP) in the QCD phase diagram. We propose a phenomenological model in which the fluctuations of the chiral critical mode couple to protons and anti-protons. This allows us to study the behavior of the net-proton number fluctuations in the presence of the CP. Calculating the net-proton number cumulants, $C_n$ with n=1,2,3,4, along the phenomenological freeze-out line we show that the ratio of variance and mean $C_2/C_1$, as well as kurtosis $C_4/C_2$ resemble qualitative properties observed in data in heavy-ion collisions as a function of beam energy obtained by the STAR Collaboration at RHIC. In particular, the non-monotonic structure of the kurtosis and smooth change of the $C_2/C_1$ ratio with beam energy could be due to the CP located near the freeze-out line. The skewness, however, exhibits properties that are in contrast to the criticality expected due to the CP. The dependence of our results on the model parameters and the proximity of the chemical freeze-out to the critical point are also discussed.

19 pages, 5 figures. Version accepted for publication in Journal of Physics G: Nuclear and Particle Physics

References in corpus (19)

• The order of the quantum chromodynamics transition predicted by the standard model of particle physics
• Chiral crossover in QCD at zero and non-zero chemical potentials
• The phase boundary for the chiral transition in (2+1)-flavor QCD at small values of the chemical potential
• K*(892)${}^0$ and $\Phi$(1020) production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV
• The QCD phase diagram at nonzero quark density
• Chiral phase transition temperature in (2+1)-Flavor QCD
• Proto-Neutron and Neutron Stars in a Chiral SU(3) Model
• Freeze-out conditions from net-proton and net-charge fluctuations at RHIC
• Dynamic universality class of the QCD critical point
• Quark Number Fluctuations in a Chiral Model at Finite Baryon Chemical Potential
• Density fluctuations in the presence of spinodal instabilities
• Chiral phase transition in the presence of spinodal decomposition
• Hyperons in thermal QCD: A lattice view
• Nucleon-Meson Coupling Constants and Form Factors in the Quark Model
• Time-evolution of fluctuations as signal of the phase transition dynamics in a QCD-assisted transport approach
• Lattice QCD results on cumulant ratios at freeze-out
• Net-baryon multiplicity distribution consistent with lattice QCD
• Fluctuations and the QCD Phase Diagram
• Parametrization for chemical freeze-out conditions from net-charge fluctuations measured at RHIC

Cited by in corpus (5)

• Freezing Out Fluctuations in Hydro+ Near the QCD Critical Point
• Factorial cumulants from global baryon number conservation
• Factorial cumulants from short-range correlations and global baryon number conservation
• Cumulants from fluctuating width of rapidity distribution
• Cumulants from short-range correlations and baryon number conservation - next-to-leading order