Universitätspublikationen
3 search hits
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Intermediate mass dileptons from secondary Drell-Yan processes
(1998)
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Christian Spieles
Lars Gerland
Nils Hammon
Marcus Bleicher
Steffen A. Bass
Horst Stöcker
Walter Greiner
C. Lourenco
Ramona Vogt
- Recent reports on enhancements of intermediate and hight mass muon pairs producedin heavy ion collisions have attracted much attention.
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Excitation function of energy density and partonic degrees of freedom in relativistic heavy ion collisions
(1998)
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H. Weber
Christoph Ernst
Marcus Bleicher
Larissa V. Bravina
Horst Stöcker
Walter Greiner
Christian Spieles
Steffen A. Bass
- We estimate the energy density epsilon pile-up at mid-rapidity in central Pb+Pb collisions from 2 200 GeV/nucleon. epsilon is decomposed into hadronic and partonic contributions. A detailed analysis of the collision dynamics in the framework of a microscopic transport model shows the importance of partonic degrees of freedom and rescattering of leading (di)quarks in the early phase of the reaction for Elab 30 GeV/nucleon. In Pb+Pb collisions at 160 GeV/nucleon the energy density reaches up to 4 GeV/fm3, 95% of which are contained in partonic degrees of freedom.
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Charmonium suppression from purely geometrical effects
(1998)
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Nils Hammon
Lars Gerland
Horst Stöcker
Walter Greiner
- The extend to which geometrical effects contribute to the production and suppression of the J/psi and qq minijet pairs in general is investigated for high energy heavy ion collisions at SPS, RHIC and LHC energies. For the energy range under investigation, the geometrical e ects referred to are shadowing and anti-shadowing, respectively. Due to those effects, the parton distributions in nuclei deviate from the naive extrapolation from the free nucleon result; fA 6= AfN. The strength of the shadowing/anti-shadowing e ect increases with the mass number. Therefore it is interesting to see the di erence between cross sections for e.g. S+U vs. Pb+Pb at SPS. The recent NA50 results for the survival probability of produced J/psi s has attracted great attention and are often interpreted as a signature of a quark gluon plasma. This publication will present a fresh look on hard QCD e ects for the charmonium production level. It is shown that the apparent suppression of J/psi s must also be linked to the production process. Due to the uncertainty in the shadowing of gluons the suppression of charmonium states might not give reli- able information on a created plasma phase at the collider energies soon available. The consequences of shadowing e ects for the xF distribution of J/psi s at s = 20 GeV, s = 200 GeV and s = 6 TeV are calculated for some relevant combinations of nuclei, as well as the pT distribution of minijets at midrapidity for Nf = 4 in the final state.
