3,396 research outputs found
The Statistical Model of Hadrogenesis in A--A collisions from AGS to SPS and RHIC
We discuss experimental data on particle yields and particle spectra obtained
in heavy ion collisions in a very broad energy range from SIS/GSI through
AGS/BNL up to SPS/CERN and RHIC/BNL. We argue that in this broad energy range
hadronic yields and their ratios resemble a thermal equilibrium population
along a unified freeze--out curve determined by the condition of fixed
energy/particle = 1 GeV. At RHIC and top SPS, thermal parameters are consistent
within error with the critical conditions required for deconfinement. This,
together with the particular distribution of strangeness within a collision
fireball, could indicate that chemical equilibrium is a direct consequence of
parton to hadron transition, which populates a state of maximum entropy. At
lower energies equilibration in A--A collisions should appear through hadronic
interactions and rescatterings.Comment: Plenary talk given at: International Nuclear Physics Conference,
INPC2001, Berkeley, USA, August 200
Strangeness enhancement and Energy dependence in Heavy Ion Collisions
The canonical statistical model analysis of strange and multistrange hadron
production in central A-A relative to p-p/p-A collisions is presented over the
energy range from GeV up to GeV. It is shown that
the relative enhancement of strange particle yields from p-p/p-A to A-A
collisions substantially increases with decreasing collision energy. It is
largest at GeV, where the enhancement of and
is of the order of 100, 20 and 3, respectively. In terms of the model
these results are due to the canonical suppression of particle thermal phase
space at lower energies, which increases with the strangeness content of the
particle and with decreasing size of the collision fireball. The comparison of
the model with existing data on energy dependence of the kaon/pion ratio is
also discussed
Probability distributions in statistical ensembles with conserved charges
The probability distributions for charged particle numbers and their
densities are derived in statistical ensembles with conservation laws. It is
shown that if this limit is properly taken then the canonical and grand
canonical ensembles are equivalent. This equivalence is proven on the most
general, probability distribution level.Comment: 5 pages. A little bit shorter version due to some editorial and
language changes. To be published in Phys. Rev.
Charmonium Production from the Secondary Collisions at LHC Energy
We consider the charmonium production in thermalized hadronic medium created
in ultrarelativistic heavy ion collisions at LHC energy.
The calculations for the secondary and production by annihilation are performed within a kinetic model taking into account the
space-time evolution of a longitudinally and transversely expanding medium. We
show that the secondary charmonium production appears almost entirely during
the mixed phase and it is very sensitive to the charmonium dissociation cross
section with co-moving hadrons. Within the most likely scenario for the
dissociation cross section of the mesons their regeneration in the
hadronic medium will be negligible. The secondary production of mesons
however, due to their large cross section above the threshold, can
substantially exceed the primary yield.Comment: ps file 11
The canonical effect in statistical models for relativistic heavy ion collisions
Enforcing exact conservation laws instead of average ones in statistical
thermal models for relativistic heavy ion reactions gives raise to so called
canonical effect, which can be used to explain some enhancement effects when
going from elementary (e.g. pp) or small (pA) systems towards large AA systems.
We review the recently developed method for computation of canonical
statistical thermodynamics, and give an insight when this is needed in analysis
of experimental data.Comment: 4 pages, 3 figures. Talk given in Strangeness in Quark Matter,
Frankfurt am Main 2001. Submitted to J. Phys. G: Nucl. Part. Phy
Kurtosis and compressibility near the chiral phase transition
The properties of net quark number fluctuations in the vicinity of the QCD
chiral phase transition are discussed in terms of an effective chiral model in
the mean-field approximation. We focus on the ratio of the fourth- to second-
order cumulants (kurtosis) and the compressibility of the system and discuss
their dependence on the pion mass. It is shown that near the chiral phase
transition, both observables are sensitive to the value of . For
physical , the kurtosis exhibits a peak whereas the inverse
compressibility shows a dip at the pseudocritical temperature. These structures
disappear for large . Our results, obtained in an effective model with
two flavors, are qualitatively consistent with recent results of 2+1 flavor
lattice gauge theory. We also discuss the high- and low-temperature properties
of these observables and the role of the coupling of the quark degrees of
freedom to the Polyakov loop
Shear and bulk viscosities of the gluon plasma in a quasiparticle description
Shear and bulk viscosities of deconfined gluonic matter are investigated
within an effective kinetic theory by describing the strongly interacting
medium phenomenologically in terms of quasiparticle excitations with
medium-dependent self-energies. We show that the resulting transport
coefficients reproduce the parametric dependencies on temperature and coupling
obtained in perturbative QCD at large temperatures and small running coupling.
The extrapolation into the non-perturbative regime results in a decreasing
specific shear viscosity with decreasing temperature, exhibiting a minimum in
the vicinity of the deconfinement transition, while the specific bulk viscosity
is sizeable in this region falling off rapidly with increasing temperature. The
temperature dependence of specific shear and bulk viscosities found within this
quasiparticle description of the pure gluon plasma is in agreement with
available lattice QCD results.Comment: Sep 2011. 24pp. 6 figures. revised journal versio
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