7 research outputs found
Charge fluctuations in chiral models and the QCD phase transition
We consider the Polyakov loop-extended two flavor chiral quark--meson model
and discuss critical phenomena related with the spontaneous breaking of the
chiral symmetry. The model is explored beyond the mean-field approximation in
the framework of the functional renormalisation group. We discuss properties of
the net-quark number density fluctuations as well as their higher cumulants. We
show that with the increasing net-quark number density, the higher order
cumulants exhibit a strong sensitivity to the chiral crossover transition. We
discuss their role as probes of the chiral phase transition in heavy-ion
collisions at RHIC and LHC.Comment: 4 pages, 3 figures, to appear in the proceedings of Quark Matter
2011, 23-28 May 2011, Annecy, Franc
The renormalization group and quark number fluctuations in the Polyakov loop extended quark-meson model at finite baryon density
Thermodynamics and the phase structure of the Polyakov loop-extended two
flavors chiral quark--meson (PQM) model is explored beyond the mean-field
approximation. The analysis of the PQM model is based on the functional
renormalization group (FRG) method. We formulate and solve the renormalization
group flow equation for the scale-dependent thermodynamic potential in the
presence of the gluonic background field at finite temperature and density. We
determine the phase diagram of the PQM model in the FRG approach and discuss
its modification in comparison with the one obtained under the mean-field
approximation. We focus on properties of the net-quark number density
fluctuations as well as their higher moments and discuss the influence of
non-perturbative effects on their properties near the chiral crossover
transition. We show, that with an increasing net-quark number density the
higher order moments exhibit a peculiar structure near the phase transition. We
also consider ratios of different moments of the net-quark number density and
discuss their role as probes of deconfinement and chiral phase transitions
Net-proton probability distribution in heavy ion collisions
We compute net-proton probability distributions in heavy ion collisions
within the hadron resonance gas model. The model results are compared with data
taken by the STAR Collaboration in Au-Au collisions at sqrt(s_{NN})= 200 GeV
for different centralities. We show that in peripheral Au-Au collisions the
measured distributions, and the resulting first four moments of net-proton
fluctuations, are consistent with results obtained from the hadron resonance
gas model. However, data taken in central Au-Au collisions differ from the
predictions of the model. The observed deviations can not be attributed to
uncertainties in model parameters. We discuss possible interpretations of the
observed deviations.Comment: 4 pages, 2 figure
Net-charge probability distributions in heavy ion collisions at chemical freeze-out
We explore net charge probability distributions in heavy ion collisions
within the hadron resonance gas model. The distributions for strangeness,
electric charge and baryon number are derived. We show that, within this model,
net charge probability distributions and the resulting fluctuations can be
computed directly from the measured yields of charged and multi-charged
hadrons. The influence of multi-charged particles and quantum statistics on the
shape of the distribution is examined. We discuss the properties of the net
proton distribution along the chemical freeze-out line. The model results
presented here can be compared with data at RHIC energies and at the LHC to
possibly search for the relation between chemical freeze-out and QCD cross-over
lines in heavy ion collisions.Comment: 21 pages, 6 figure
Fluctuations as probe of the QCD phase transition and freeze-out in heavy ion collisions at LHC and RHIC
We discuss the relevance of higher order moments of net baryon number
fluctuations for the analysis of freeze-out and critical conditions in heavy
ion collisions at LHC and RHIC. Using properties of O(4) scaling functions, we
discuss the generic structure of these higher moments at vanishing baryon
chemical potential and apply chiral model calculations to explore their
properties at non-zero baryon chemical potential. We show that the ratios of
the sixth to second and eighth to second order moments of the net baryon number
fluctuations change rapidly in the transition region of the QCD phase diagram.
Already at vanishing baryon chemical potential they deviate considerably from
the predictions of the hadron resonance gas model which reproduce the second to
fourth order moments of the net proton number fluctuations at RHIC. We point
out that the sixth order moments of baryon number and electric charge
fluctuations remain negative at the chiral transition temperature. Thus, they
offer the possibility to probe the proximity of the thermal freeze-out to the
crossover line.Comment: 24 pages, 12 EPS files, revised version, to appear in EPJ