CMeurer PPTWin

Hyperon production in Pb+Pb collisions@: 

Hyperon production in Pb+Pb collisions @ Christine Meurer J. W. Goethe-Universität / Frankfurt for the NA49 collaboration SPS

Outline: 

New data: X and W at 40AGeV, L at 30AGeV Transverse distribution Longitudinal distribution Energy dependence of hyperon production Centrality dependence of X- production at 40AGeV Summary and Outlook Outline

New data: 

New data L at 30 AGeV X and W at 40 AGeV L minv (GeV/c2) Entries minv (GeV/c2) Entries minv (GeV/c2) Entries

Transverse distribution: mT –spectra: 

Transverse distribution: mT –spectra Spectra at mid-rapidity Fit range: 0.2-1.4 Exponential fit does not describe spectra very well at low and high mT range. 158 AGeV 40 AGeV L at 40 and 158AGeV: nucl-ex/0311024 at 158AGeV: Phys. Lett. B 538 (2002) 275 W at 158AGeV: Nucl. Phys. A 715 (2003) 161c  L,  X,  W preliminary preliminary Pb+Pb (7%) Pb+Pb (10%) 20%

Transverse distribution: mass dependence of T: 

Transverse distribution: mass dependence of T Open symbols: antiparticles p K pfL X W Light particles show a linear increase of T with mass. For heavier particles T seems to saturate, but on different levels for different energies. preliminary

Transverse distribution: blast wave fit: 

Transverse distribution: blast wave fit Similar parameters for both energy. Radial flow fit: r = atanh bT Schnedermann, Sollfrank, Heinz Phys. Rev. C 48 (1993) 2462 Good description of the spectra, also for low mT range. Same procedure for K- and K+ preliminary preliminary

Transverse distribution: blast wave fit parameters: 

Transverse distribution: blast wave fit parameters 40 AGeV: Slight differences of the parameters for X+W and for K-+K+ 158 AGeV: Similar parameters No evidence for early decoupling of X and W preliminary preliminary

Longitudinal distribution: rapidity spectra: 

sys. error ~ 10% Longitudinal distribution: rapidity spectra A clear evolution of shape of L is visible. No big change of shape of X and W with energy. 158 AGeV 80 AGeV 40 AGeV 30 AGeV  L,  X,  W preliminary preliminary preliminary

Energy dependence of hyperon production: 

Energy dependence of hyperon production Ls show a distinct maximum at 30AGeV. For Xs and Ws a weak maximum is indicated. Y = L, X-, W-+W+ AGS data: E895 Hadron-gas model: Braun-Munzinger, Cleymans, Öschler, Redlich Nucl. Phys. A697 (2002) 902 x6 x15 x 6 x 15 preliminary 4p yields

Energy dependence of B/B at mid-rapidity: 

Energy dependence of B/B at mid-rapidity Energy dependence of B/B changes with strangeness content of the particles. preliminary

Centrality dependence of X- at 40AGeV: 

Centrality dependence of X- at 40AGeV At 40AGeV the X--production shows a saturation effect from mid-central to central reactions. See also: “System size dependence” poster at this conference presented by Ingrid Kraus preliminary

Summary: 

Summary New data: X, W at 40AGeV, L at 30AGeV in Pb+Pb collisions Transverse distributions: Mt-spectra: no good description by exponential fit but by blast wave fit No evidence of early decoupling of X and W Longitudinal distributions: Rapidity spectra: clear evolution of shape of L from 30 to 158AGeV, Gausian shape for X and W at 40 and 158AGeV Energy dependence: Distinct maximum at 30AGeV for L/p-,weak maximum for X/p- and W/p- B/B-ratio: energy dependence changes with strangeness content Centrality dependence of X-/NW at 40AGeV: Increase from peripheral to mid-central and followed by saturation Outlook: Complete analysis of hyperons with data at 20, 30, 40, 80, and 158AGeV