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CERN Heavy Ion Forum
Hadron Production in ultra-relativistic Nuclear Collision - Rolf Hagedorns legacy
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Europe/Zurich
160/1-009 (CERN)
Description
1. The horn and the unreasonable success of the thermal model
by Johanna Stachel
Abstract
We present, using the statistical model, a new analysis of hadron production in central collisions of heavy nuclei. This study is motivated by the availability of final measurements both for the SPS (beam energies 20-160 AGeV) and for the RHIC energies (sqrt(sNN) =130 and 200 GeV) and by updates in the hadron mass spectrum, which is a crucial input for statistical models. Extending previous studies by inclusion of very high-mass resonances (m> 2 GeV), and the up-to-now neglected scalar meson leads to an improved description of the data. In particular, the hitherto poorly reproduced energy dependence of the K+/pi+ ratio at SPS energies is now well described through the connection to the hadronic mass spectrum and, implicitly, Hagedorn'sYs limiting temperatur e.We thereby demonstrate the intimate connection between the horn and the QCD phase transition.
2. What happens at the transition from baryonic to mesonic freeze out?
by Helmut Oeschler
Abstract
The statistical model assuming chemical equilibrium describes most of the observed features of strange particle production from SIS up to RHIC. Deviations are found as the maximum in the measured K+/pi+ ratio as a function of sqrt(s) is much sharper than in the model calculations. At the location of the maximum (sqrt(s) = 7 - 8 GeV), the statistical model shows that the freeze out changes regime from being dominated by baryons at the lower energies toward one being dominated by mesons. It will be shown how deviations from the usual freeze-out curve might influence the various particle ratios. Furthermore, other observables exhibit also changes just in this energy regime.
3. Centrality dependence of observables in HI reactions - more than a core-corona effect ?
by Joerg Aichelin
Abstract
Strangeness enhancement in heavy ion collisions is since long a highly debated subject.
Based on the results of one of the event generators (EPOS) we have proposed a very simple model which describes the centrality dependence of the multiplicities of all measured hadrons from SPS to RHIC energies among those that of (multi)strange baryons.
The idea behind is that only a fraction of the colliding nucleons form an equilibrated source (core) whereas others (corona) scatter only once and disintegrate like in a pp collisions. The core/corona fraction depends on energy and centrality and can be calculated in a Glauber model. Recently we have shown that also the centrality dedependence of kinetical variables are well described in this model, among those the centrality dependence of the elliptic flow v2. This rises the question whether this dependence allows for determination of the viscosity of the QGP as proposed by different hydro groups.
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EVO information: Title:HIF
Description: HIF - 160-1-009
Community: ALICE
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Organised by
Y. Foka, U. Wiedemann