arXiv subjects

Jean Letessier

Publications and source records attributed to Jean Letessier.

At least 55 records · Page 3Linked to original sources

arXiv1999

Low-m_t charged pion asymmetry enhancement from hadronization of QGP

We show that in sudden hadronization of QGP a non-equilibrium value of the pion phase space occupancy parameter gamma_q>1 is expected in order to accommodate the entropy excess in QGP and the process of gluon fragmentation. When gamma_q is near to its maximum allowed value, pion overabundance is shown to arise at low $m_\bot$, where the charged pion asymmetry is also amplified. These effects are considered and we show that their magnitude suffices to explain pertinent experimental data obtained in 160-200AGeV Pb- and S- induced reactions.

nucl-th↗

arXiv1999

Diagnosis of QGP with Strange Hadrons

We review the current status of strangeness as signature of the formation and dissociation of the deconfined QGP at the SPS energy scale, and present the status of our considerations for RHIC energies. By analyzing, within the framework of a Fermi statistical model, the hadron abundance and spectra, the properties of a disintegrating, hadron evaporating, deconfined QGP fireball are determined and can be compared with theory for the energy range 160--200AGeV on fixed target. We discuss in more detail our finding that the pion yields occur near to pion condensation condition. Dynamical models of chemical strangeness equilibration are developed and applied to obtain strangeness production in a QGP phase at conditions found at SPS and expected at RHIC. The sudden QGP break up model that works for the SPS data implies at RHIC dominance of both baryon, and antibaryon, abundances by the strange baryon and antibaryon yields.

hep-ph↗

arXiv1999

Expected Production of Strange Baryons and Antibaryons in Baryon-Poor QGP

In a dynamical model of QGP at RHIC we obtain the temporal evolution of strange phase space occupancy at conditions expected to occur in 100+100A GeV nuclear collisions. We show that the sudden QGP break up model developed to describe the SPS experimental results implies dominance of both baryon and antibaryon abundances by the strange baryon and antibaryon yields.

nucl-th↗

arXiv1999

Hadron production in Pb-Pb collisions at 158A GeV

A Fermi statistical model analysis of hadron abundances and spectra obtained in several relativistic heavy ion collision experiments is utilized to characterize a particle source. Properties consistent with a disintegrating, hadron evaporating, deconfined quark-gluon plasma phase fireball are obtained, with a baryochemical potential μ_B=200-210MeV, and a temperature T_f\simeq 140-150MeV, significantly below previous expectations.

nucl-th↗

arXiv1999

Hadron Freeze-out and QGP Hadronization

Abundances and $m_\bot$-spectra of strange and other hadronic particles emanating from central 158-200 A GeV reactions between nuclei are found to originate from a thermally equilibrated, deconfined source in chemical non-equilibrium. Physical freeze-out parameters and physical conditions (pressure, specific energy, entropy, and strangeness) are evaluated. Five properties of the source we obtain are as expected for direct hadron emission (hadronization) from a deconfined quark-gluon plasma phase.

hep-ph↗

arXiv1998

Chemical Nonequilibrium in High Energy Nuclear Collisions

Strange particles produced in S-Au/W/Pb 200 A GeV and Pb-Pb 158 A GeV reactions are described invoking final hadronic phase space in thermal equilibrium, but allowing chemical non-equilibrium. Several sets of statistical freeze-out parameters are obtained for each system, invoking different models of dense matter. We show that only when allowing for strange and non-strange flavor abundance non-equilibrium, a statistically significant description of the experimental results is obtained. Physical properties of the fireball at chemical freeze-out condition are evaluated and considerable universality of hadron freeze-out between the two different collision systems is established. The relevance of the Coulomb effect in the highly charged Pb-Pb fireballs for the chemical analysis are discussed. The influence of explosive collective matter flow is also described.

hep-ph↗

arXiv1998

Quark-Gluon Plasma in Pb--Pb 158 A GeV collisions: Evidence from strange particle abundances and the Coulomb effect

The hadronic particle production data from relativistic nuclear Pb--Pb 158 A GeV collisions are successfully described within the chemical non-equilibrium model, provided that the analysis treats Omega and anti-Omega abundances with care. We further show that there is a subtle influence of the Coulomb potential on strange quarks in quark matter which is also seen in our data analysis, and this Coulomb effect confirms the finding made by chemical analysis in the S--Au/W/Pb 200 A GeV collisions that the hadron particle source is deconfined with respect to strange quark propagation. Physical freeze-out conditions (pressure, specific energy, entropy, and strangeness) are evaluated and considerable universality of hadron freeze-out between the two different collision systems is established.

hep-ph↗

arXiv1998

Chemical non-equilibrium and deconfinement in 200 A GeV Sulphur induced reactions

We interpret hadronic particle abundances produced in S--Au/W/Pb 200 A GeV reactions in terms of the final state hadronic phase space model and determine by a data fit of the chemical hadron freeze-out parameters. Allowing for the flavor abundance non-equilibrium a highly significant fit to experimental particle abundance data emerges, which supports possibility of strangeness distillation. We find under different strategies stable values for freeze-out temperature T_f=143\pm3 MeV, baryochemical potential μ_B= 173\pm6 MeV, ratio of strangeness (γ_s) and light quark (γ_q) phase space occupancies γ_s/γ_q=0.60\pm0.02, and γ_q=1.22\pm0.05 without accounting for collective expansion (radial flow). When introducing flow effects which allow a consistent description of the transverse mass particle spectra, yielding |v_c|=0.49\pm0.01c, we find γ_s/γ_q=0.69\pm0.03, γ_q=1.41\pm0.08. The strange quark fugacity is fitted at λ_s=1.00\pm0.02 suggesting chemical freeze-out directly from the deconfined phase.

hep-ph↗

arXiv1997

Energy Dependence of Strange Particle Yields from a QGP-Fireball

We explore, as function of the collision energy and stopping in relativistic nuclear collisions, the production yields of strange particles, in particular strange antibaryons,assuming formation of a deconfined thermal QGP-fireball which undergoes a sudden hadronisation. The non-equilibrium freeze-out conditions are established and strange antibaryon excitation functions are shown to have characteristic features that should allow to discriminate between the QGP hypothesis and other reaction scenarios.

hep-ph↗

arXiv1997

Formation and Evolution of the Quark-Gluon Plasma

Imposing an equilibrium between the thermal pressure of deconfined quarks and gluons and the dynamical compression pressure exercised by in-flowing nuclear matter, we study the initial thermal conditions reached in a quark-gluon plasma fireball formed in a relativistic heavy ion collision. We show that entropy is produced primarily in the pre-equilibrium stage of the reaction. We test our approach, comparing our results with the S-W/Pb collision results at 200 GeV A and find a surprising degree of agreement assuming about 50% stopping. We apply our method to a determination of the conditions in collisions of Au-Au at 11 GeV A and Pb-Pb at 157 GeV A, assuming full stopping of momentum, energy and baryon number. Our detailed results directly determine the spectral shape and abundance of (strange) hadrons and electromagnetic probes (photons, dileptons) produced in the collision, and we explore specific experimental consequences.

hep-ph↗

arXiv1997

Strangeness and Particle Freeze-out in Nuclear Collisions at 14.6 Gev a

We study the chemical conditions at freeze-out associated with the production of strange-particles in Si-Au collisions at 14.6 GeV A. We obtain freeze-out chemical potentials and temperature, and determine the entropy as well as the final particle abundance. We also consider in detail the alternative evolution scenarios involving the hadronic gas and the deconfined phase.

hep-ph↗

arXiv1997

QGP Formation and Strange Antibaryons

We analyze current experimental results and explore, as function of the collision energy and stopping in relativistic nuclear collisions, the production yields of strange antibaryons, assuming formation of a deconfined thermal QGP-fireball which undergoes a sudden hadronisation.

hep-ph↗

arXiv1997

Strange anti-baryons - QGP versus HG

We study quark-gluon plasma (QGP) and hadronic gas (HG) models of the central fireball presumed to be the source of abundantly produced strange (anti-)baryons in S -> W collisions at 200 GeV A. We consider how multi-strange (anti-)baryon multiplicities depend on strangeness conservation and compare the HG and QGP fireball scenarios. We argue that the total particle multiplicity emerging from the central rapidity region as well as the variation of production rates with changes in the beam energy allows to distinguish between the two reaction scenarios.

hep-ph↗

arXiv1997

Gluon production, cooling and entropy in nuclear collisions

We study the cooling (heating) of a glue-parton gas due to production (destruction) of particles and determine the associated production of entropy. We incorporate sharing of the system energy among a changing number of particles. We find that the entropy of an evolving glue-parton gas changes in an insignificant range once the initial high temperature state has been formed, despite a great change in particle number and temperature.

hep-ph↗

arXiv1997

Strange Particle Freeze-Out

We reconsider thermal conditions of the central fireball presumed to be the source of abundantly produced strange (anti-)baryons in S -> W collisions at 200 GeV A. We show that it is possible to completely fix the freeze-out temperature of strange particles in terms of the central rapidity kaon to Lambda particle abundance ratio at fixed, high transverse mass using a non-equilibrium hadronization model and the measured quark fugacities.

hep-ph↗

arXiv1997

Hot hadronic matter and strange anti-baryons

We demonstrate that both quark-gluon plasma (QGP) and hadronic gas (HG) models of the central fireball created in S -> W collisions at 200 GeV A are possible sources of the recently observed strange (anti-) baryons. From the theoretical point of view, the HG interpretation we attempt remains more obscure because of the high fireball temperature required. The thermal properties of the fireball as determined by the particle ratios, are natural for the QGP state. We show that the total particle multiplicity emerging from the central rapidity region allows to distinguish between the two scenarios.

hep-ph↗

arXiv1997

Strange Particle Abundance in QGP Formed in 200 GeV A Nuclear Collisions

We investigate here the relative abundance of strange particles produced in nuclear collisions at the SPS energies (9 GeV A in CM frame) assuming that the central reaction fireball consists of quark-gluon plasma. We show that the total strangeness yield in S-S, S-Ag and S-W reactions is compatible with this picture.

hep-ph↗

arXiv1997

Strange Antibaryons from QGP

We study as function of the collision energy and stopping the thermal conditions reached in a quark-gluon plasma fireball formed in a relativistic heavy ion collision. We explore strange particle yields for the current round of Pb-Pb and Au-Au experiments.

hep-ph↗