Quark-gluon Plasma Formation Research Articles

Possible indirect evidences of quark-gluon plasma formation

Through unitarity the formation of the quark-gluon plasma can influence other kinds of processes. This effect is studied within a simple three-channel eikonal model: the answer, obtained through a numerical analysis, is that in the elastic channel the opening of this new inelastic channel might produce a sizable signal.

Possible signature for and early hadronization mechanisms of quark-gluon plasma

We consider the ratio of particle abundances radiated from quark-gluon plasma above mean thermal energy and point out signigicant differences expected as compared with global particle yields. Two microscopic processes leading to medium to high E ⊥ abundances are quantitatively considered and the means of determining the plasma baryochemical potential are discussed. Strong anomalies in strange antibaryon spectra are found, characteristic of the formation of quark-gluon plasma.

Separation of strangeness from antistrangeness in the phase transition from quark to hadron matter: Possible formation of strange quark matter in heavy-ion collisions

We present a mechanism for the separation of strangeness from antistrangeness in the deconfinement transition. For a net strangeness of zero in the total system, the population of s quarks is greatly enriched in the quark-gluon plasma, while the s\ifmmode\bar\else\textasciimacron\fi{} quarks drift into the hadronic phase. This separation could result in ``strangelet'' formation, i.e., metastable blobs of strange-quark matter, which could serve as a unique signature for quark-gluon plasma formation in heavy-ion collisions.

Pre-equilibrium plasma dynamics

Approaches towards understanding and describing the pre-equilibrium stage of quark-gluon plasma formation in heavy-ion collisions are reviewed.

J/ψ suppression by quark-gluon plasma formation

If high energy heavy ion collisions lead to the formation of a hot quark-gluon plasma, then colour screening prevents cc binding in the deconfined interior of the interaction region. To study this effect, the temperature dependence of the screening radius, as obtained from lattice QCD, is compared with the J/ψ radius calculated in charmomium models. The feasibility to detect this effect clearly in the dilepton mass spectrum is examined. It is concluded that J/ψ suppression in nuclear collisions should provide an unambiguous signature of quark-gluon plasma formation.

Lambda 0 nonpolarization: Possible signature of quark matter.

The polarization of the lambda hyperons, produced in proton- and nucleus-induced interactions over a wide range of incident energies and target masses, is examined. The persistence and con- stancy of the polarization up to the highest energy measured is consistent with the absence of quark-gluon plasma in these reactions. It is suggested that, in ultrarelativistic heavy ion collisions, the formation of quark-gluon plasma in the central region will result in the diminishing of the polarization of central rapidity lambdas.

Thermalization in ultrarelativistic heavy ion collisions: Parton cascade approach.

A parton cascade model is formulated for ultrarelativistic heavy ion collisions. The model is used to determine the degree of thermalization, as well as energy and baryon number densities in central collisions of heavy ions at ultrarelativistic energies. It is shown that the energy densities required for quark-gluon plasma formation can easily be reached at $\sqrt{{s}_{\mathrm{NN}}}$ less than 100 GeV.

Stopping of heavy nuclei in relativistic heavy-ion collisions.

We examine the space-time dynamics of the baryons in nucleus-nucleus collisions and estimate the energy density reached in the central rapidity region. It is found that with an incident laboratory energy of 15 GeV per projectile nucleon, a headon collision of Au on Au will leave a substantial spatial region with an energy density of 1.5--3 GeV/${\mathrm{fm}}^{3}$ which may exceed the energy density for a quark-gluon plasma formation.

How much strangeness production is there in ultrarelativistic nucleus-nucleus collisions?

Strangeness production has been proposed as a signal for the formation of a quark-gluon plasma in ultrarelativistic nucleus-nucleus collisions. We address this problem in the framework of Bjorken's model for the longitudinal hydrodynamic expansion of baryon-free matter. Different scenarios are considered for the assumed first-order phase transition from QCD plasma into hadrons, including a slow transition via the Maxwell construction of coexisting phases, and a rapid transition from supercooling followed by reheating. The rate equations for strange-quark and kaon abundances are solved numerically. With the most likely set of parameters, the ${K}^{\mathrm{\ensuremath{-}}}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ ratio is about three times larger than in p\ifmmode\bar\else\textasciimacron\fi{}p collisions at the same energy. This results primarily from the large rate constant in the hadron phase and from the long time spent in this phase. Thus, the ${K}^{\mathrm{\ensuremath{-}}}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ ratio may not be a direct signal for the formation of quark-gluon plasma; however, it may be an indirect signal, since the system would not live nearly as long if the quark-gluon plasma had not been formed initially.

Possible manifestation of quark-gluon plasma in ultra-relativistic nucleus-nucleus collisions

The written version of this lecture concentrates mainly on recent developments concerning possible detection of quark-gluon plasma formation and covers them at greater length than the oral presentation. The topics covered are: • - early energy and entropy densities, fluctuations, transverse flow, • - dilepton emission by high temperature plasma, • - thermalization, plasma formation versus string and chain models.

Strangeness production as a signal for quark-gluon plasma formation in high energy particle collisions

Strangeness production in hot nuclear matter in the non-interacting gas approximation with anUB(1)×US(1) internal symmetry group is discussed. It is argued that the strangeness abundancy ratio in the quark-gluon plasma as compared to the hadron gas strongly depends on under which thermodynamical circumstances it has been computed.

Transverse-momentum distribution of produced particles in ultrarelativistic nucleus-nucleus collisions.

In order to discern coherent or collective processes from incoherent processes in nucleus-nucleus reactions at high energies, we study the transverse-momentum distribution of the produced particles with an incoherent-multiple-collision model. In this model, the projectile nucleon makes successive inelastic collisions with nucleons in the target nucleus, the probability of such collisions being given by the thickness function and the nucleon-nucleon inelastic cross section. It is assumed that each baryon-baryon collision produces particles and degrades momenta just as a baryon-baryon collision in free space, and that there are no secondary collisions between the produced particles and the nucleons. We found that the average transverse momentum and the charged-multiplicity data at Fermilab and CERN ISR energies can be well explained by such a model. However, the average transverse momentum for some events observed by the Japanese-American cooperative emulsion experiment (JACEE) associated with large energy density in the central rapidity region differ markedly from the model results. Such a deviation indicates the presence of coherent or collective effects for these collisions and may indicate the possibility of a formation of quark-gluon plasma.

Quark-gluon plasma formation in the central rapidity region and finite size effects of colliding nuclei

The energy density of the central products in the ultra-relativistic heavy ion collisions are calculated. In our estimation, the special attention is paid to the space-time extension of the emission points of the secondary hadrons which are originate in the successive nucleon-nucleon interactions within the finite size of colliding nuclei. The average collision number per produced particle, in the final state interaction, is also calculated and is used as a criterion whether the system is thermalized or not. It turns out that the attainable energy density in the central heavy ion collision is sensitive to the spacetime extension of the emission points. However, if the incident energy and the mass numbers of colliding nuclei are high and large, we can get high enough energy density for the phase transition from a hadronic state to a quark-gluon plasma state.

FastJ/Ψ's as a signal for quark-gluon plasma formation

The production ofJ/Ψ's as a signal for the formation of a quark-gluon plasma in collisions between ions is discussed. Calculations are based on the fusion of two gluons into aJ/Ψ and an additional gluon to conserve colour. Comparisons between normal and thermal production rates are made.

Energies and mass numbers needed for the Quark-Gluon plasma formation

The energy density of the centrally produced system in ultra-relativistic heavy ion collisions and its dependences on the incident energy and on nuclear mass numbers are systematically studied based on the multi-chain model. The relaxation time of the system is estimated and is incorporated in the evaluation of the energy density. It turns out that a thermalized system, having enough energy density for quark-gluon plasma formation, is surely obtained.

Deconfinement in the baryon rich region

The dynamics of deconfinement and hadronization at high chemical potentials, i.e. in baryon rich matter, are discussed. Quark gluon plasma formation in the fragmentation regions is characterized by low temperatures. Condensation discontinuities are predicted which result in substantial entropy production during hadronization in the fragmentation regions, by far exceeding the entropy expected if deconfinement would not occur. This excess entropy may be useful for plasma diagnostics, since it is directly related to the coupling strength and nonperturbative effects in the deconfined phase. Energy densities of 1 – 2 GeV/fm 3 are obtained in stopping collisions of heavy nuclei at bombarding energies E lab = 5–10 GeV/n.

The lund monte carlo for e +e − jet physics

The lund monte carlo for e +e − jet physics

Nucleus-nucleus collisions: Observations and expectations

Selected topics of nucleus-nucleus collisions between MeV/u and TeV/u are discussed, covering some recent experiments on fusion and fusion-like processes in the heavy element regime at energies around the Coulomb-barrier, some experiments on ternary exit channels at the borderline to intermediate energies and some possible future experiments on signals associated with quark-gluon plasma formation at ultrarelativistic energies.

Quark-gluon plasma formation in heavy ion collisions and quarkochemistry

Improving our quarkochemical model by an energy balance equation we point out that quark-gluon plasma formation is energetically impossible below E lab ≈ 6 GeV/ nucleon bombarding energy in heavy ion collisions. We compare the predictions for the observed hadronic composition of the hadrochemical and quarkochemical model. We find that one consequence of the quark matter formation will be a decrease in the meson production, corresponding to a low temperature of the plasma, instead of the large increase expected before.