Probing the QCD phase diagram with fluctuations

Abstract

The relevance of higher order cumulants of conserved charges for the analysis of freeze-out and critical conditions in heavy ion collisions at LHC and RHIC is discussed. Using properties of O(4) scaling functions, the generic structure of these higher cumulants at vanishing baryon chemical potential is discussed. Chiral model calculations are then used to study their properties at non-zero baryon chemical potential. It is argued that the rapid variation of sixth and higher order cumulants at the phase boundary may be used to explore the QCD phase diagram in experiment. Moreover, results for the Polyakov loop susceptibilities in SU(3) lattice gauge theory as well as in (2+1) flavor lattice QCD are discussed. An analysis of the ratios of susceptibilities indicates that the deconfinement transition is reflected in characteristic modifications of these ratios.

Exploring the QCD Phase Structure with Beam Energy Scan in Heavy-ion Collisions

“…For different observables, the behavior near the QCD critical point could be very different. As illustrated in Fig.6 right, according to the theoretical calculations [34,35,36,37], the critical contributions to the observable κσ 2 consist of positive and negative two sub-regions displayed as blue and red in Fig.6 right, respectively. Experimentally, in addition to the statistical baseline unity, the sign of critical contributions for the κσ 2 depends on the relative position of chemical freeze-out and the critical contribution region.…”

Baryon number fluctuations and the phase structure in the PNJL model

“…Therefore, the event-by-event measurements of statistical distributions of fluctuations of conserved charges are crucial in searching for QCD phase structure [22,23]. The measurement of high-order fluctuations have been already suggested to explore the QCD phase transition (e.g., [24][25][26][27][28][29][30][31][32][33][34][35]). Recently, the preliminary result of the first phase of STAR Beam Energy Scan (BES-I) in Au+Au collisions indicates that the kurtosis of net-proton number fluctuation presents a non-monotonic energy dependence and a large deviation from the Poisson baseline [36][37][38].…”

“…The baryon number fluctuations are investigated recently in different models, for example, the NJL model [39,40], the Polyakov Loop extended Quark Meson model [41], the functional renormalization group approach [42], the DSE approach [18], the interacting hadronic model [43,44] and the holographic QCD model [45]. Up to now the interpretation of the experimental results remains controversial [28][29][30][31]39,41,43,44] and phase transformation mechanism leading to the non-monotonic energy dependence of net proton kurtosis is still not clear.…”

Effects of nuclear potential on the cumulants of net-proton and net-baryon multiplicity distributions in Au+Au collisions atsNN=5GeV

“…Due to sign problem in Lattice QCD calculations at finite baryon density, there are large uncertainties to determine the location of critical point by theoretical and/or QCD based model calculations [5,6]. The fluctuation of conserved quantities, such as net-baryon number, and its proxy observable net-proton number, served as the observable sensitive to the correlation length of nuclear matter [7][8][9][10], have been extensively studied experimentally [11][12][13] and theoretically [14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”