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Centrality and beam energy dependence of HBT radii at SPS
by Harald Appelshaeuser (University of Heidelberg) for the CERES collaboration
We present preliminary results of a two-pion HBT interferometry analysis, performed by the CERES/NA45 experiment at the CERN-SPS. The centrality dependence of HBT radii from 40, 80, and 158 A GeV Pb+Au collisions will be shown. We also discuss possible conclusions about the lifetime, the transverse flow velocity and the phase space density of the system at freeze-out, characterizing the space-time evolution. Our results will be put into perspective with HBT results from different experiments and at different bombarding energies.
The HBT Puzzle at RHIC
by Boris Tomasik (CERN TH Division)
Before the HBT data for RHIC were taken, theoretical predictions expected large correlation radii and a clear signal of a long lifetime visible through a large ratio of outward-to-sideward radius. None of these expectations fulfilled. The data indicate a strongly expanding fireball which seems to explode instantaneously rather than emit particles over a longer time. In a thermal model fit this would require very low freeze-out temperature. In order to understand the size of HBT radii a measurement of pion phase-space density is crucial. Despite of an earlier suggestion that the freeze-out phase-space density is a universal quantity, the data from STAR indicate an increase when compared to SPS energy. This will be, to a large part, an overview talk about what the data show and how we (don't) understand them.
Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann / EP Division
Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann / EP Division