19 research outputs found
Quark Gluon Bags as Reggeons
The influence of the medium dependent finite width of QGP bags on their
equation of state is analyzed within an exactly solvable model. It is argued
that the large width of the QGP bags not only explains the observed deficit in
the number of hadronic resonances, but also clarifies the reason why the heavy
QGP bags cannot be directly observed as metastable states in a hadronic phase.
The model allows us to estimate the minimal value of the width of QGP bags from
a variety of the lattice QCD data and get that the minimal resonance width at
zero temperature is about 600 MeV, whereas the minimal resonance width at the
Hagedorn temperature is about 2000 MeV. As shown these estimates are almost
insensitive to the number of the elementary degrees of freedom. The recent
lattice QCD data are analyzed and it is found that besides sigma T**4 term the
lattice QCD pressure contains T-linear and T**4 ln T terms in the range of
temperatures between 240 MeV and 420 MeV. The presence of the last term in the
pressure bears almost no effect on the width estimates. Our analysis shows that
at hight temperatures the average mass and width of the QGP bags behave in
accordance with the upper bound of the Regge trajectory asymptotics (the linear
asymptotics), whereas at low temperatures they obey the lower bound of the
Regge trajectory asymptotics (the square root one). Since the model explicitly
contains the Hagedorn mass spectrum, it allows us to remove an existing
contradiction between the finite number of hadronic Regge families and the
Hagedorn idea of the exponentially growing mass spectrum of hadronic bags.Comment: One section removed, a few references added, the Regge trajectories
of free QGP bags are considere
Exactly Solvable Model for the QCD Tricritcal Endpoint
An inclusion of temperature and chemical potential dependent surface tension
into the gas of quark-gluon bags model resolves a long standing problem of a
unified description of the first and second order phase transition with the
cross-over. The suggested model has an exact analytical solution and allows one
to rigorously study the vicinity of the critical endpoint of the deconfinement
phase transition. It is found that at the curve of a zero surface tension
coefficient there must exist the surface induced phase tranition of the 2-nd or
higher order. The present model predicts that the critical endpoint (CEP) of
quantum chromodynamics is the tricritical endpoint.Comment: 14 pages, 3 figures, invited talk given at the International Workshop
``Relativistic Nuclear Physics: from Nuclotron to LHC Energies'', Kiev,
Ukraine, June 18-22, 200
Hadron Resonance Gas Model with Induced Surface Tension
Here we present a physically transparent generalization of the multicomponent
Van der Waals equation of state in the grand canonical ensemble. For the
one-component case the third and fourth virial coefficients are calculated
analytically. It is shown that an adjustment of a single model parameter allows
us to reproduce the third and fourth virial coefficients of the gas of hard
spheres with small deviations from their exact values. A thorough comparison of
the compressibility factor and speed of sound of the developed model with the
one and two component Carnahan-Starling equation of state is made. It is shown
that the model with the induced surface tension is able to reproduce the
results of the Carnahan-Starling equation of state up to the packing fractions
0.2-0.22 at which the usual Van der Waals equation of state is inapplicable. At
higher packing fractions the developed equation of state is softer than the gas
of hard spheres and, hence, it breaks causality in the domain where the
hadronic description is expected to be inapplicable. Using this equation of
state we develop an entirely new hadron resonance gas model and apply it to a
description of the hadron yield ratios measured at AGS, SPS, RHIC and ALICE
energies of nuclear collisions. The achieved quality of the fit per degree of
freedom is about 1.08. We confirm that the strangeness enhancement factor has a
peak at low AGS energies, while at and above the highest SPS energy of
collisions the chemical equilibrium of strangeness is observed. We argue that
the chemical equilibrium of strangeness, i.e. , observed
above the center of mass collision energy 4.3 GeV may be related to the
hadronization of quark gluon bags which have the Hagedorn mass spectrum, and,
hence, it may be a new signal for the onset of deconfinement
Fresh look at the Hagedorn mass spectrum as seen in the experiments
The medium dependent finite width is introduced into an exactly solvable
model with the general mass-volume spectrum of the QGP bags. The model allows
us to estimate the minimal value of the QGP bags' width from the lattice QCD
data. The large width of the QGP bags not only explains the observed deficit in
the number of hadronic resonances comparing to the Hagedorn mass spectrum, but
also clarifies the reason why the heavy QGP bags cannot be directly observed as
metastable states in a hadronic phase.Comment: 6 pages, no figures, accepted to Europhys. Let
Hard-core Radius of Nucleons within the Induced Surface Tension Approach
In this work we discuss a novel approach to model the hadronic and nuclear
matter equations of state using the induced surface tension concept. Since the
obtained equations of state, classical and quantum, are among the most
successful ones in describing the properties of low density phases of strongly
interacting matter, they set strong restrictions on the possible value of the
hard-core radius of nucleons. Therefore, we perform a detailed analysis of its
value which follows from hadronic and nuclear matter properties and find the
most trustworthy range of its values: the hard-core radius of nucleons is
0.30--0.36 fm. A comparison with the phenomenology of neutron stars implies
that the hard-core radius of nucleons has to be temperature and density
dependent.Comment: 12 pages, 4 figures, references added, typos correcte
Evidence of the QCD Tricritical Endpoint Existence at NICA-FAIR Energies
We present a summary of possible signals of the chiral symmetry restoration and deconfinement phase transitions which may be, respectively, probed at the center of mass collision energies at 4.3-4.9 GeV and above 8.7-9.2 GeV. It is argued that these signals may evidence for an existence of the tricritical endpoint of QCD phase diagram at the collision energy around 8.7-9.2 GeV. The equation of state hadronic matter with the restored chiral symmetry is discussed and the number of bosonic and fermionic degrees of freedom is found
Second virial coefficients of light nuclear clusters and their chemical freeze-out in nuclear collisions
Here we develop a new strategy to analyze the chemical freeze-out of light
(anti)nuclei produced in high energy collisions of heavy atomic nuclei within
an advanced version of the hadron resonance gas model. It is based on two
different, but complementary approaches to model the hard-core repulsion
between the light nuclei and hadrons. The first approach is based on an
approximate treatment of the equivalent hard-core radius of a roomy nuclear
cluster and pions, while the second approach is rigorously derived here using a
self-consistent treatment of classical excluded volumes of light (anti)nuclei
and hadrons. By construction, in a hadronic medium dominated by pions, both
approaches should give the same results. Employing this strategy to the
analysis of hadronic and light (anti)nuclei multiplicities measured by ALICE at
TeV and by STAR at GeV, we got rid
of the existing ambiguity in the description of light (anti)nuclei data and
determined the chemical freeze-out parameters of nuclei with high accuracy and
confidence. At ALICE energy the nuclei are frozen prior to the hadrons at the
temperature MeV, while at STAR energy there is a
single freeze-out of hadrons and nuclei at the temperature
MeV. We argue that the found chemical freeze-out volumes of nuclei can be
considered as the volumes of quark-gluon bags that produce the nuclei at the
moment of hadronization.Comment: 15 pages, 4 figures, 3 table
Chemical equilibration due to heavy Hagedorn states
A scenario of heavy resonances, called massive Hagedorn states, is proposed
which exhibits a fast ( fm/c) chemical equilibration of (strange)
baryons and anti-baryons at the QCD critical temperature . For
relativistic heavy ion collisions this scenario predicts that hadronization is
followed by a brief expansion phase during which the equilibration rate is
higher than the expansion rate, so that baryons and antibaryons reach chemical
equilibrium before chemical freeze-out occurs.Comment: 9 pages, 2 figures. Invited talk given at 8th International
Conference on Strangeness in Quark Matter (SQM2004), Cape Town, South Africa,
15-20 September 200