150 research outputs found
Effect of finite particle number sampling on baryon number fluctuations
The effects of finite particle number sampling on the net baryon number
cumulants, extracted from fluid dynamical simulations, are studied. The
commonly used finite particle number sampling procedure introduces an
additional Poissonian (or multinomial if global baryon number conservation is
enforced) contribution which increases the extracted moments of the baryon
number distribution. If this procedure is applied to a fluctuating fluid
dynamics framework one severely overestimates the actual cumulants. We show
that the sampling of so called test-particles suppresses the additional
contribution to the moments by at least one power of the number of
test-particles. We demonstrate this method in a numerical fluid dynamics
simulation that includes the effects of spinodal decomposition due to a first
order phase transition. Furthermore, in the limit where anti-baryons can be
ignored, we derive analytic formulas which capture exactly the effect of
particle sampling on the baryon number cumulants. These formulas may be used to
test the various numerical particle sampling algorithms.Comment: 9 pages 3 figure
Spinodal amplification of density fluctuations in fluid-dynamical simulations of relativistic nuclear collisions
Extending a previously developed two-phase equation of state, we simulate
head-on relativistic lead-lead collisions with fluid dynamics, augmented with a
finite-range term, and study the effects of the phase structure on the
evolution of the baryon density. For collision energies that bring the bulk of
the system into the mechanically unstable spinodal region of the phase diagram,
the density irregularities are being amplified significantly. The resulting
density clumping may be exploited as a signal of the phase transition, possibly
through an enhanced production of composite particles.Comment: 4 pages 4 figures, version accepted by PR
QCD Equation of State From a Chiral Hadronic Model Including Quark Degrees of Freedom
This work presents an effective model for strongly interacting matter and the
QCD equation of state (EoS). The model includes both hadron and quark degrees
of freedom and takes into account the transition of chiral symmetry restoration
as well as the deconfinement phase transition. At low temperatures and
baryonic densities a hadron resonance gas is described using a
SU(3)-flavor sigma-omega model and a quark phase is introduced in analogy to
PNJL models for higher and . In this way, the correct asymptotic
degrees of freedom are used in a wide range of and . Here, results
of this model concerning the chiral and deconfinement phase transitions and
thermodynamic model properties are presented. Large hadron resonance
multiplicities in the transition region emphasize the importance of heavy-mass
resonance states in this region and their impact on the chiral transition
behavior. The resulting phase diagram of QCD matter at small chemical
potentials is in line with latest lattice QCD and thermal model results.Comment: 5 pages 3 figures; presented at the 8th International Workshop on
"Critical Point and Onset of Deconfinement - CPOD 2013" Napa, March 11-15,
201
The QCD Phase Diagram from Statistical Model Analysis
Ideally, the Statistical Hadronization Model (SHM) freeze-out curve should
reveal the QCD parton-hadron phase transformation line in the (,)
plane. We discuss the effects of various final state interaction phenomena,
like baryon-antibaryon annihilation, core-corona effects or QCD critical point
formation, which shift or deform the SHM freezeout curve. In particular, we
present a method to remove the annihilation effects by quantifying them with
the microscopic hadron transport model UrQMD. We further discuss the new
aspects of hadronization that could be associated with the relatively broad
cross-over phase transformation as predicted by lattice-QCD theory at low
. That opens up the possibility that various observables of
hadronization, e.g. hadron formation or susceptibilities of higher order
(related to grand canonical fluctuations of conserved hadronic charges) may
freeze out at different characteristic temperatures. This puts into question
the concept of a universal \textit{(pseudo-)critical} temperature, as does the
very nature of a cross-over phase transformation.Comment: 24 pages, 11 figures. Submitted as part of the Walter Greiner
memorial boo
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