Interferometry search for new forms of matter in A+A collisions

A method allowing studies of the hadronic matter at the early evolution stage in A+A collisions is developed. It is based on an interferometry analysis of approximately conserved values such as the averaged phase-space density (APSD) and the specific entropy of thermal pions. The plateau found in the APSD behavior vs collision energy at SPS is associated, apparently, with the deconfinement phase transition at low SPS energies; a saturation of this quantity at the RHIC energies indicates the limiting Hagedorn temperature for hadronic matter.Comment: 4 pages, 3 figures, contribution to the Quark Matter 2005 proceedings, minor change

Simple solutions of fireball hydrodynamics for self-similar elliptic flows

Simple, self-similar, elliptic solutions of non-relativistic fireball hydrodynamics are presented, generalizing earlier results for spherically symmetric fireballs with Hubble flows and homogeneous temperature profiles. The transition from one dimensional to three dimensional expansions is investigated in an efficient manner.Comment: 12 pages, 4 figures in 8 .eps files, references to recent data added, accepted in Physics Letters

Reconstruction of Hadronization Stage in Pb+Pb Collisions at 158A GeV/c

Recent data on hadron multiplicities in central Pb+Pb collisions at 158A GeV/c at mid-rapidity are analyzed within the concept of chemical freeze-out. A non-uniformity of the baryon chemical potential along the beam axis is taken into account. An approximate analytical solution of the hydrodynamic equations for a chemically frozen Boltzmann-like gas is found. The Cauchy conditions for hydrodynamic evolution of the hadron resonance gas are fixed at the thermal freeze-out hypersurface from analysis of one-particle momentum spectra and HBT correlations. The proper time of chemical freeze-out and physical conditions at the hadronization stage, such as energy density and averaged transverse velocity, are found.Comment: 21 pages including 3 figures, RevTex, semi-relativistic solution of hydrodynamics was used, submitted to Nucl. Phys.

Many--Particle Correlations in Relativistic Nuclear Collisions

Many--particle correlations due to Bose-Einstein interference are studied in ultrarelativistic heavy--ion collisions. We calculate the higher order correlation functions from the 2--particle correlation function by assuming that the source is emitting particles incoherently. In particular parametrizations of and relations between longitudinal, sidewards, outwards and invariant radii and corresponding momenta are discussed. The results are especially useful in low statistics measurements of higher order correlation functions. We evaluate the three--pion correlation function recently measured by NA44 and predict the 2--pion--2--kaon correlation function. Finally, many particle Coulomb corrections are discussed.Comment: 5 corrected misprints, 14 pages, revtex, epsfig, 6 figures included, manuscript also available at http://www.nbi.dk/~vischer/publications.htm

Correlation search for coherent pion emission in heavy ion collisions

The methods allowing to extract the coherent component of pion emission conditioned by the formation of a quasi-classical pion source in heavy ion collisions are suggested. They exploit a nontrivial modification of the quantum statistical and final state interaction effects on the correlation functions of like and unlike pions in the presence of the coherent radiation. The extraction of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation functions and single--pion spectra is discussed in detail for large expanding systems produced in ultra-relativistic heavy ion collisions.Comment: 21 pages, 3 eps figures, ReVTeX, corrected submission abstract. Version published in PRC 65 (2002) 064904. Added is a detailed explanation of the differences between pure coherent states and charge constrained coherent states in the case of a simple example model. The expressions for two-particle spectra taking into account both the final state interaction and the coherent component of pion emission are derived in a more general and transparent wa

The freeze-out mechanism and phase-space density in ultrarelativistic heavy-ion collisions

We explore the consequences of a freeze-out criterion for heavy-ion collisions, based on pion escape probabilities from the hot and dense but rapidly expanding collision region. The influence of the expansion and the scattering rate on the escape probability is studied. The temperature dependence of this scattering rate favors a low freeze-out temperature of ~100 MeV. In general, our results support freeze-out along finite four-volumes rather than sharp three-dimensional hypersurfaces, with high-pt particles decoupling earlier from smaller volumes. We compare our approach to the proposed universal freeze-out criteria using the pion phase-space density and its mean free path.Comment: 8 pages, 2 figures, although conclusions are unchanged, the paper has been re-written and the title has been changed for the sake of better presentatio

The Bose-Einstein correlation function C2(Q)C_2(Q) from a Quantum Field Theory point of view

We show that a recently proposed derivation of Bose-Einstein correlations (BEC) by means of a specific version of thermal Quantum Field Theory (QFT), supplemented by operator-field evolution of the Langevin type, allows for a deeper understanding of the possible coherent behaviour of the emitting source and a clear identification of the origin of the observed shape of the BEC function $C_2(Q)$. Previous conjectures in this matter obtained by other approaches are confirmed and have received complementary explanation.Comment: Some misprints corrected. To be publishe in Phys. Rev.

Heavy ion event generator HYDJET++ (HYDrodynamics plus JETs)

HYDJET++ is a Monte-Carlo event generator for simulation of relativistic heavy ion AA collisions considered as a superposition of the soft, hydro-type state and the hard state resulting from multi-parton fragmentation. This model is the development and continuation of HYDJET event generator (Lokhtin & Snigirev, 2006, EPJC, 45, 211). The main program is written in the object-oriented C++ language under the ROOT environment. The hard part of HYDJET++ is identical to the hard part of Fortran-written HYDJET and it is included in the generator structure as a separate directory. The soft part of HYDJET++ event is the "thermal" hadronic state generated on the chemical and thermal freeze-out hypersurfaces obtained from the parameterization of relativistic hydrodynamics with preset freeze-out conditions. It includes the longitudinal, radial and elliptic flow effects and the decays of hadronic resonances. The corresponding fast Monte-Carlo simulation procedure, C++ code FAST MC (Amelin et al., 2006, PRC, 74, 064901; 2008, PRC, 77, 014903) is adapted to HYDJET++. It is designed for studying the multi-particle production in a wide energy range of heavy ion experimental facilities: from FAIR and NICA to RHIC and LHC.Comment: 44 pages including 6 figures as EPS-files; prepared using LaTeX package for publication in Computer Physics Communication

Microscopic study of freeze-out in relativistic heavy ion collisions at SPS energies

The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding systems of heavy nuclei at 160 AGeV/$c$ are analyzed within the microscopic Quark Gluon String Model (QGSM). We found that even for the most heavy systems particle emission takes place from the whole space-time domain available for the system evolution, but not from the thin ''freeze-out hypersurface", adopted in fluid dynamical models. Pions are continuously emitted from the whole volume of the reaction and reflect the main trends of the system evolution. Nucleons in Pb+Pb collisions initially come from the surface region. For both systems there is a separation of the elastic and inelastic freeze-out. The mesons with large transverse momenta, $p_t$, are predominantly produced at the early stages of the reaction. The low $p_t$-component is populated by mesons coming mainly from the decay of resonances. This explains naturally the decreasing source sizes with increasing $p_t$, observed in HBT interferometry. Comparison with S+S and Au+Au systems at 11.6 AGeV/$c$ is also presented.Comment: REVTEX, 26 pages incl. 9 figures and 2 tables, to be published in the Physical Review