Strangeness Production in Chemically Non-Equilibrated Parton Plasma

Strangeness production was investigated during the equilibration of a gluon dominated parton plasma produced at RHIC and LHC energies. The time evolution of parton densities are followed by a set of rate equations in a 1-dimensional expanding system. The strangeness production will depend on the initial chemical equilibration level and in our case the parton densities will remain far from the full equilibrium. We investigate the influence of gluon fragmentation on final strangeness content.Comment: 12 pages (LaTeX) + 2 postscript figures (tarred, compressed, uuencoded) included. Review to appear in Proceedings of Strangeness'95, Tucson, Arizona, Jan. 4--6 1995. (American Institute of Physics

Scaling of hadronic transverse momenta in a hydrodynamic treatment of relativistic heavy ion collisions

The transverse momenta of hadrons in central nucleus-nucleus collisions are evaluated in a boost invariant hydrodynamics with transverse expansion. Quark gluon plasma is assumed to be formed in the initial state which expands and cools via a first order phase transition to a rich hadronic matter and ultimately undergoes a freeze-out. The average transverse momentum of pions, kaons, and protons is estimated for a wide range of multiplicity densities and transverse sizes of the system. For a given system it is found to scale with the square-root of the particle rapidity density per unit transverse area, and consistent with the corresponding values seen in $p\overline{p}$ experiments at 1800 GeV, suggesting a universal behaviour. The average transverse momentum shows only an approximate scaling with multiplicity density per nucleon which is at variance with the $p\overline{p}$ data.Comment: 6 pages including 9 figure

Strangeness Production at RHIC in the Perturbative Regim

We investigate strange quark production in Au-Au collisions at RHIC in the framework of the Parton Cascade Model(PCM). The yields of (anti-) strange quarks for three production scenarios -- primary-primary scattering, full scattering, and full production -- are compared to a proton-proton baseline. Enhancement of strange quark yields in central Au-Au collisions compared to scaled p-p collisions increases with the number of secondary interactions. The centrality dependence of strangeness production for the three production scenarios is studied as well. For all production mechanisms, the strangeness yield increases with $(N_{\rm part})^{4/3}$. The perturbative QCD regime described by the PCM is able to account for up to 50% of the observed strangeness at RHIC.Comment: 10 pages, 4 figures, IOP forma

Non-Abelian Energy Loss at Finite Opacity

A systematic expansion in opacity, $L/\lambda$, is used to clarify the non-linear behavior of induced gluon radiation in quark-gluon plasmas. The inclusive differential gluon distribution is calculated up to second order in opacity and compared to the zeroth order (factorization) limit. The opacity expansion makes it possible to take finite kinematic constraints into account that suppress jet quenching in nuclear collisions below RHIC ($\sqrt{s}=200$ AGeV) energies.Comment: 4 pages (revtex) with 3 eps figures, submitted to PR

The charged-hadron/pion ratio at the Relativistic Heavy Ion Collider

The hadron/pion ratio is calculated in 200 GeV AuAu collisions at midrapidity, applying pQCD and non-universal transverse-momentum broadening. Arguments are presented for such non-universality, and the idea is implemented in a model, which explains the enhancement of the hadron/pion ratio in central AuAu collisions. The model also describes the qualitative difference between the recently-measured dAu nuclear enhancement factors for pions and charged hadrons.Comment: 4 pages, 3 figure

A Comment on Conical Flow Induced by Heavy-Quark Jets

The suppression of high transverse momentum particles, recently discovered at RHIC, is commonly interpreted as due to parton energy loss. In high energy nuclear collisions, QCD jets would deposit a large fraction of their energy and into the produced matter. The question of how this energy is degraded and whether we can use this phenomenon to probe the properties of the produced matter is now under active discussion. It has been proposed that if this matter, which is now being referred to as a {\em strongly coupled Quark-Gluon Plasma} (sQGP), may behave as a liquid with a very small viscosity. In this case, a very specific collective excitation should be produced, called the ``conical flow'', similar e.g. to the sonic booms generated by the shock waves produced by supersonic planes. The RHIC experiments seem indeed to be obtaining some indication that the production of particles emitted opposite to a high-$p_t$ jet may actually be peaked away from the quenched jet direction, at an angle roughly consistent with the direction expected in case a shock wave is produced (i.e. orthogonal to the Mach cone). In this note we speculate that for tagged heavy-quark jets one may observe a shrinkage of the Mach cone at moderate $p_t$. The experimental observation of such an effect would be a very good test for the validity of the whole picture currently emerging from the study of partonic matter in nuclear collisions

Jet tomography

I summarize the recent advances in jet tomographic studies of cold and hot nuclear matter based on perturbative QCD calculations of medium-induced gluon bremsstrahlung. Quantitative applications to ultrarelativistic heavy ion reactions at RHIC indicate the creation of a deconfined state of QCD with initial energy density on the order of 100 times cold nuclear matter density.Comment: Plenary talk given at the seventeenth international conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004). 8 pages, 12 figures. Updated references, updated Table

Evolution of strangeness in equilibrating and expanding quark-gluon plasma

We evaluate the strangeness production from equilibrating and transversely expanding quark gluon plasma which may be created in the wake of relativistic heavy ion collisions. We consider boost invariant longitudinal and cylindrically symmetric transverse expansion of a gluon dominated partonic plasma, which is in local thermal equilibrium. Initial conditions obtained from the self screened parton cascade model are used. We empirically find that the final extent of the partonic equilibration rises almost linearly with the square of the initial energy density. This along with the corresponding variation with the number of participants may help us distinguish between various models of parton production.Comment: RevTex, 10 pages including 6 figures comprising 11 postscript files, text modified considerably with an added figure (Fig. 6) and this version accepted for publication in Phys. Rev.

Predictions for p+p+Pb Collisions at sNN=5\sqrt{s_{NN}} = 5 TeV: Comparison with Data

Predictions made in Albacete {\it et al} prior to the LHC $p+$Pb run at $\sqrt{s_{NN}} = 5$ TeV are compared to currently available data. Some predictions shown here have been updated by including the same experimental cuts as the data. Some additional predictions are also presented, especially for quarkonia, that were provided to the experiments before the data were made public but were too late for the original publication are also shown here.Comment: 55 pages 35 figure

High-p_T pion and kaon production in relativistic nuclear collisions

High-p_T pion and kaon production is studied in relativistic proton-proton, proton-nucleus, and nucleus-nucleus collisions in a wide energy range. Cross sections are calculated based on perturbative QCD, augmented by a phenomenological transverse momentum distribution of partons (``intrinsic k_T''). An energy dependent width of the transverse momentum distribution is extracted from pion and charged hadron production data in proton-proton/proton-antiproton collisions. Effects of multiscattering and shadowing in the strongly interacting medium are taken into account. Enhancement of the transverse momentum width is introduced and parameterized to explain the Cronin effect. In collisions between heavy nuclei, the model over-predicts central pion production cross sections (more significantly at higher energies), hinting at the presence of jet quenching. Predictions are made for proton-nucleus and nucleus-nucleus collisions at RHIC energies.Comment: 26 pages in Latex, 19 EPS figure