München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 39: Physik mit schweren Ionen

HK 39.1: Gruppenbericht

Mittwoch, 22. März 2006, 16:30–17:00, D

Scale Dependence of Mean Transverse Momentum Fluctuations at Top SPS Energy — •Georgios Tsiledakis — Gesellschaft für Schwerionenforschung (GSI), Darmstadt

Non-statistical event-by-event fluctuations of mean transverse momentum, p_T, have been proposed as a possible signature for the QCD phase transition, in particular for the critical point. A surprising finding was that a small but practically beam energy independent value was found for the broad energy range of 40 AGeV at SPS up to top RHIC energy. Since fluctuations were characterized so far by one single (integral) number, it was difficult to estimate the many possible contributions to them. Taking into account the high available statistics offered by the CERES experiment combined with the full azimuthal acceptance, a differential study of mean p_T fluctuations is performed, which by allowing to discriminate among various correlation sources, provides the sensitivity to the fluctuations related to the vicinity of critical point. For the first time at SPS energy, the charge-dependent mean p_T fluctuations have been analyzed as a function of the angular pair separation, Δφ, and of the separation in pseudorapidity, Δη. The results show that the overall fluctuations are dominated by the short range correlation peak at small opening angles (‘near-side’), most probably originating from Bose-Einstein and Coulomb effects. Another important contribution is a broad maximum at Δφ=180^o (‘away-side’) originating from back-to-back (dijet-like) correlations. Concerning the observed away-side peak, we demonstrate that it comes from high-p_T correlations that cannot be attributed to elliptic flow.