arXiv subjects
Publications and source records attributed to Jan Pisut.
We describe a model of jet quenching in nuclear collisions at RHIC energies. In the model, jet quenching is to be caused by the interruption of jet formation by nucleons arriving at the position of jet formation in a time shorter than the jet formation time. Our mechanism predicts suppression of high-pt spectra also in d+Au reactions.
We present a few estimates of energy densities reached in heavy-ion collisions at the CERN SPS. The estimates are based on data and models of proton-nucleus and nucleus-nucleus interactions. In all of these estimates the maximum energy density in central Pb+Pb interactions is larger than the critical energy density of about 0.7 GeV/fm^3 following from lattice gauge theory computations. In estimates which we consider as realistic the maximum energy density is about twice the critical value. In this way our analysis gives some support to claims that deconfined matter has been produced at the CERN SPS. Any definite statement requires a deeper understanding of formation times of partons and hadrons in nuclear collisions. We also compare our results with implicit energy estimates contained in earlier models of anomalous J/psi suppression in nuclear collisions.
We propose a simple Glauber-type mechanism for suppression of jet production up to transverse momenta of about 10 GeV/c at RHIC. For processes in this kinematic region, the formation time is smaller than the interval between two successive hard partonic collisions and the subsequent collision influences the jet production. Number of jets then roughly scales with the number of participants. Proportionality to the number of binary collisions is recovered for very high transverse momenta. The model predicts suppression of jet production in d+Au collisions at RHIC.
We propose an alternative way of looking at data on anomalous J/psi suppression. The proposed method is in principle equivalent to the one used by the NA50 Collaboration, but it permits to visualize separate contributions of individual processes responsible for the disintegration of J/psi's produced by a hard process in nuclear collisions. The method can be used provided that the time sequence of contributing mechanisms is known or assumed. It offers an alternative graphical presentation of the onset of anomalous J/psi suppression in Pb-Pb interactions observed by the NA50 Collaboration at the CERN SPS and might contribute to explain why different mechanisms, such as J/psi suppression by the Quark-Gluon Plasma and by co-movers in the Dual Parton Model or in Monte Carlo microscopic approaches, all lead to an approximate description of anomalous J/psi suppression.
The enhanced suppression of $J/ψ$ production at large $x_F$ in $pA$ collisions is studied in the framework of gluon depletion at large $x_1$. The nonperturbative process that modifies the gluon distribution as the gluons propagate in nuclear matter is described by an evolution equation with a kernal to be determined by phenomenology. With nuclear shadowing and anti-shadowing taken into account, the effect on the gluon distribution is shown to be a depletion in excess of 40% at $x_1 \approx 0.8$ for $A > 100$. There is a small amount of enhancement of the gluon distribution at small $x_1$, but it does not lead to any contradiction with the existing data on $J/ψ$ suppression in the central region. Extentions to $ψ^{\prime}$ suppression and $AB$ collisions are also investigated in the framework of gluon redistribution.
We point out that data on the onset of anomalous J/psi suppression as a function of nucleon numbers A and B could provide information on the dynamics of nuclear interactions. In particular the models of anomalous J/psi suppression by Blaizot and Ollitrault (BO) and by Kharzeev, Lourenco, Nardi and Satz (KLNS) are based on different assumptions on the dynamics of nuclear collisions and lead to different predictions of the dependence of the onset of anomalous J/psi suppression on nucleon numbers of colliding nuclei. The data on this onset as function of A and B could become a tool for the study of the dynamics of nuclear collisions and bring further evidence on J/psi suppression by new form of hadronic matter, possibly Quark-Gluon Plasma. In particular we propose to study J/ψsuppression in A+Pb interaction with nucleon number of A between 58 and 73 or a bit higher.
We propose a simple model of production of strange baryons and antibaryons in nuclear collisions at the CERN SPS. The model takes into account both the increase of strangeness production in collisions of lighter ions and a possibility of the formation of anomalous, strangeness rich matter in central PbPb interactions. It is shown that ratios like $<Ω>:<Ξ>:<Λ>$ depend strongly on the presence of anomalous matter and can be used to determine its phenomenological parameters. In the model we assume that particle composition of final state hadrons is essentially given by a rapid recombination of quarks and antiquarks formed in tube-on-tube interactions of incoming nucleons.
We argue that strong final state rescattering among the secondary particles created in relativistic heavy ion collisions is essential to understand the measured Bose-Einstein correlations. The recently suggested ``random walk models'' which contain only initial state scattering are unable to reproduce the measured magnitude and K_\perp-dependence of R_\perp in Pb+Pb collisions and the increase of R_l with increasing size of the collision system.
Data on mean numbers of $Λ$, $\barΛ$, K's and on the total number $ $ of pairs of strange valence quarks in final state hadrons in hadronic and nuclear collisions at CERN- SPS energies are studied as a function of the mean number $ $ of nucleon- nucleon collisions. Results give indications of an almost linear dependence over most of the region of $ $. This in turn points out to strangeness being produced mostly in the central rapidity region of nucleon- nucleon collisions by a mechanism similar to a hard or semi- hard process. The available data are extrapolated to Pb+Pb interactions by two simple models, leading to $ _{Pb+Pb}\approx 300\pm 30 $. Observations exceeding these values of $ _{Pb+Pb}$ would give evidence of the onset of a new dynamical regime in Pb+Pb interactions.
We point out that formation time of pions produced in heavy ion collisions modifies the mass spectrum of dileptons produced via pipi -> ee annihilation. Increasing formation time enhances the production of dileptons with lower masses. The effect offers an explanation of a part of the enhanced production of dileptons below the rho-meson mass as observed by the CERES and HELIOS Collaborations at the CERN SPS.
We point out that dissociation of J/Psi by partons (mostly gluons) present in the intermediate stage of heavy-ion collisions can explain J/Psi suppression observed recently by the NA-50 Collaboration at the CERN-SPS in Pb-Pb interactions. Suppression by intermediate stage gluons represents an additional multiplicative factor to that given by Gerschel-Hufner mechanism. The agreement with data on J/Psi suppression both in light- ions induced nuclear collisions and in Pb-Pb interactions requires that the life-time of intermediate gluons increases with nucleon numbers of colliding nuclei. In our model the energy density of intermediate stage gluons in Pb-Pb collisions approaches for a short time the critical density.
In an attempt to disentangle the effects of nuclear geometry from those of nuclear geometry we study dependence of longitudinal radius on nucleon numbers of colliding nuclei within a simple model of multiple nucleon- nucleon collisions.We discuss two approaches to resulting simple formula.In the former the data up to S-Au can be described by nuclear geometry at the price of two parameters,but R_L for Pb-Pb is significantly larger than geometry can accomodate, indicating an onset of a new dynamics. In the latter even collisions induced by lighter ions give evidence of some collective behaviour and the increase of R_L for Pb-Pb indicates again the onset of a new dynamics.