A simple model for transverse energy distribution in heavy ion collisions

A simple geometrical model (often quoted in literature as the Glauber model) of heavy ion collisions is recapitulated. It is shown that the transverse energy distribution of heavy ion collisions follow the geometry of the collision. An extension of the model to include rapidity and transverse mass particle spectra is discussed.Comment: 7 page

Strangeness production in nuclear interactions at 200 AGeV and the number of nucleon-nucleon collisions

Data on mean numbers of $\Lambda$, $\bar\Lambda$, 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.Comment: 16 pages,3 figure

Quark liberation and coalescence at CERN SPS

The mischievous linear coalescence approach to hadronization of quark matter is shown to violate strangeness conservation in strong interactions. The simplest correct quark counting is shown to coincide with the non-linear algebraic coalescence rehadronization model, ALCOR. The non-linearity of the ALCOR model is shown to cancel from its simple predictions for the relative yields of (multi-)strange baryons. We prove, model independently, that quark degrees of freedom are liberated before hadron formation in 158 AGeV central Pb + Pb collisions at CERN SPS.Comment: Latex file, 6 pages, improved text and conclusio

Canonical Description of Strangeness Enhancement from p-A to Pb-Pb Collisions

We consider the production of strange particles in Pb-Pb and p-A collisions at the SPS energy reported by the WA97 experiment. We show that the observed enhancement of strange baryon and antibaryon yields in Pb-Pb collisions relative to p-Be and p-Pb can be explained in terms of the statistical model formulated in canonical ensemble with respect to strangeness conservation. The importance and the role of strangeness under saturation is also discussed.Comment: 8 pages, 3 figure

A model of anomalous production of strange baryons in nuclear collisions

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 $::$ 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.Comment: 17 pages, 3 picture

Balance functions in coalescence model

It is shown that the quark-antiquark coalescence mechanism for pion production allows to explain the small width of the balance function observed for central collisions of heavy ions, provided effects of the finite acceptance region and of the transverse flow are taken into account. In contrast, the standard hadronic cluster model is not compatible with this data.Comment: 12 pages, 1 figur

Energy dependence of {\rm K}S0^0_{\rm S} and hyperon production at CERN SPS

Recent results on K$^0_{\rm S}$ and hyperon production in Pb-Pb collisions at 40 and 158 $A$ GeV/$c$ beam momentum from the NA57 experiment at CERN SPS are presented. Yields and ratios are compared with those measured by the NA49 experiment, where available. The centrality dependence of the yields and a comparison with the higher collision energy data from RHIC are discussed.Comment: 4 pages, 3 figures, proceedings of QM2004 conferenc

Strange Resonance Production: Probing Chemical and Thermal Freeze-out in Relativistic Heavy Ion Collisions

The production and the observability of $\Lambda(1520)$, $K^0(892)$ $\Phi$ and $\Delta(1232)$ hadron resonances in central Pb+Pb collisions at 160 AGeV is addressed. The rescattering probabilities of the resonance decay products in the systems evolution are studied. Strong changes in the reconstructable particle yields and spectra between chemical and thermal freeze-out are estimated. Abundances and spectra of reconstructable resonances are predicted.Comment: 6 pages, 5 figure

Strangeness Enhancement in Heavy Ion Collisions - Evidence for Quark-Gluon-Matter ?

The centrality dependence of (multi-)strange hadron abundances is studied for Pb(158 AGeV)Pb reactions and compared to p(158 GeV)Pb collisions. The microscopic transport model UrQMD is used for this analysis. The predicted Lambda/pi-, Xi-/pi- and Omega-/pi- ratios are enhanced due to rescattering in central Pb-Pb collisions as compared to peripheral Pb-Pb or p-Pb collisions. A reduction of the constituent quark masses to the current quark masses m_s \sim 230 MeV, m_q \sim 10 MeV, as motivated by chiral symmetry restoration, enhances the hyperon yields to the experimentally observed high values. Similar results are obtained by an ad hoc overall increase of the color electric field strength (effective string tension of kappa=3 GeV/fm). The enhancement depends strongly on the kinematical cuts. The maximum enhancement is predicted around midrapidity. For Lambda's, strangeness suppression is predicted at projectile/target rapidity. For Omega's, the predicted enhancement can be as large as one order of magnitude. Comparisons of Pb-Pb data to proton induced asymmetric (p-A) collisions are hampered due to the predicted strong asymmetry in the various rapidity distributions of the different (strange) particle species. In p-Pb collisions, strangeness is locally (in rapidity) not conserved. The present comparison to the data of the WA97 and NA49 collaborations clearly supports the suggestion that conventional (free) hadronic scenarios are unable to describe the observed high (anti-)hyperon yields in central collisions. The doubling of the strangeness to nonstrange suppression factor, gamma_s \approx 0.65, might be interpreted as a signal of a phase of nearly massless particles.Comment: published version, discussion on strange mesons and new table added, extended discussion on strange baryon yields. Latex, 20 pages, including 5 eps-figure