437 research outputs found
Directed flow in heavy-ion collisions at NICA: what is interesting to measure?
We study the formation of the directed flow of hadrons in nuclear collisions
at energies between AGS and SPS in Monte Carlo cascade model. The slope of the
proton flow at midrapidity tends to zero (softening) with increasing impact
parameter of the collision. For very peripheral topologies this slope becomes
negative (antiflow). The effect is caused by rescattering of hadrons in
remnants of the colliding nuclei. Since the softening of the proton flow can be
misinterpreted as indication of the presence of quark-gluon plasma, we propose
several measurements at NICA facility which can help one to distinguish between
the cases with and without the plasma formation.Comment: 5 pages, 3 figures, Contribution to the NICA White Paper (EPJA,
topical issue
Gluon shadowing in the Glauber-Gribov model at HERA
We calculate shadowing using new data on the gluon density of the Pomeron
recently measured with high precision at HERA. The calculations are made in a
Glauber-Gribov framework and Pomeron tree-diagrams are summed up within a
unitarity-conserving procedure. The total cross section of \vphot A
interaction is then found in a parameter-free description, employing gluon
diffractive and inclusive distribution functions as input. A strong shadowing
effect is obtained, in good agreement with several other models. Impact
parameter dependence of gluon shadowing is also presented.Comment: 18 pages, 6 figures; references added, discussion of model enlarged,
calculation of low-x contribution corrected; to appear in Phys. Let
Homogeneous nucleation of quark gluon plasma, finite size effects and longlived metastable objects
The general formalism of homogeneous nucleation theory is applied to study the hadronization pattern of the ultra-relativistic quark-gluon plasma (QGP) undergoing a first order phase transition. A coalescence model is proposed to describe the evolution dynamics of hadronic clusters produced in the nucle- ation process. The size distribution of the nucleated clusters is important for the description of the plasma conversion. The model is most sensitive to the initial conditions of the QGP thermalization, time evolution of the energy den- sity, and the interfacial energy of the plasma hadronic matter interface. The rapidly expanding QGP is first supercooled by about T = T Tc = 4 6%. Then it reheats again up to the critical temperature Tc. Finally it breaks up into hadronic clusters and small droplets of plasma. This fast dynamics occurs within the first 5 10 fm/c. The finite size e ects and fluctuations near the critical temperature are studied. It is shown that a drop of longitudinally expanding QGP of the transverse radius below 4.5 fm can display a long-lived metastability. However, both in the rapid and in the delayed hadronization scenario, the bulk pion yield is emitted by sources as large as 3 4.5 fm. This may be detected experimentally both by a HBT interferometry signal and by the analysis of the rapidity distributions of particles in narrow pT -intervals at small |pT | on an event-by-event basis. PACS numbers: 12.38.Mh, 24.10.Pa, 25.75.-q, 64.60.Q
Supercooling of rapidly expanding quark-gluon plasma
We reexamine the scenario of homogeneous nucleation of the quark-gluon plasma
produced in ultra-relativistic heavy ion collisions. A generalization of the
standard nucleation theory to rapidly expanding system is proposed. The
nucleation rate is derived via the new scaling parameter . It is
shown that the size distribution of hadronic clusters plays an important role
in the dynamics of the phase transition. The longitudinally expanding system is
supercooled to about 3-6%, then it is reheated, and the hadronization is
completed within 6-10 fm/c, i.e. 5-10 times faster than it was estimated
earlier, in a strongly nonequilibrium way.Comment: 12 pages, LaTeX, 3 eps figure
Irreversibility, steady state, and nonequilibrium physics in relativistic heavy ion collisions
Heavy ion collisions at ultrarelativistic energies offer the opportunity to study the irreversibility of multiparticle processes. Together with the many-body decays of resonances, the multiparticle processes cause the system to evolve according to Prigogine s steady states rather than towards statistical equilibrium. These results are general and can be easily checked by any microscopic string-, transport-, or cascade model for heavy ion collisions. The absence of pure equilibrium states sheds light on the di culties of thermal models in describing the yields and spectra of hadrons, especially mesons, in heavy ion collisions at bombarding energies above 10 GeV/nucleon. PACS numbers: 25.75.-q, 05.70.Ln, 24.10.L
Gluon shadowing and unitarity effects
New data from HERA experiment on deep inelastic scattering have been used to
parametrize nucleon and Pomeron structure functions. Within the Gribov theory,
the parameterizations were employed to calculate gluon shadowing for various
heavy ions. The latter was compared with predictions from other models.
Calculations of multiplicity reduction due to gluon shadowing for d+Au
collisions at forward rapidities at =200 GeV are in good agreement
with BRAHMS data on the nuclear modification factor.Comment: 5 pages, 4 figures, submitted to Acta Physica Hungarica A, Quark
Matter 2005 poster session proceedings; minor changes in the text adde
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