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NA49 energy scan results for central Pb-Pb collisions at the SPS

NA49 energy scan results for central Pb-Pb collisions at the SPS. Michiel Botje, NIKHEF (for the NA49 collaboration). Aim: search for indications of the onset of deconfinement from a study of the energy dependence of particle production in central Pb+Pb collisions. NA49.

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NA49 energy scan results for central Pb-Pb collisions at the SPS

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  1. NA49 energy scan results for central Pb-Pb collisions at the SPS Michiel Botje, NIKHEF (for the NA49 collaboration) Aim: search for indications of the onset of deconfinement from a study of the energy dependence of particle production in central Pb+Pb collisions M. Botje, Rencontres de Moriond on QCD, March 2004

  2. NA49 Large acceptance hadron spectrometer p/p2 = (0.3 – 7)  10–4 (GeV/c)–1 PID by dE/dx in TPCs for p > 7 GeV/c PID by TOF (~60 ps) at mid-rapidity Centrality selection from spectators indownstream VCAL (not shown) M. Botje, Rencontres de Moriond on QCD, March 2004

  3. Beam Energy Centrality Event Statistics Taken in 158 AGeV 10 % 800 k 1996 158 AGeV 20 % 3000 k 2000 80 AGeV 7 % 300 k 2000 40 AGeV 7 % 700 k 1999 30 AGeV 7 % 400 k 2002 20 AGeV 7 % 300 k 2002 NA49 central Pb+Pb data sets • 158, 80, 40 AGeV published in PRC 66(2003)054902 • 30, 20 AGeV still preliminary M. Botje, Rencontres de Moriond on QCD, March 2004

  4. Blast wave fits 158AGeV r = atanh bT T = kinetic freeze-out temperature T = transverse flow velocity Schnedermann, Sollfrank, Heinz: PRC 48(1993)2462 Transverse mass spectra at mid-rapidity Not included in fit: pions (resonance decays) and deuterons (coalescence) M. Botje, Rencontres de Moriond on QCD, March 2004

  5. Transverse mass spectra at lower energies 40 AGeV 30 AGeV 20 AGeV • Blast wave model describes spectra at all SPS energies • Kinetic freeze-out at T  120-130 MeV and T  0.4-0.5 M. Botje, Rencontres de Moriond on QCD, March 2004

  6. Exponential fits to kaon mT spectra • Constant slopes in the SPS energy range M. Botje, Rencontres de Moriond on QCD, March 2004

  7. No rise of inverse slope in SPS energy range • Consequence of constant pressure in mixed phase? (van Hove, 1982) Energy dependence of slope parameters M. Botje, Rencontres de Moriond on QCD, March 2004

  8. (Open circles: reflection about mid-rapidity) Rapidity spectra versus energy Also  and  Large acceptance  exptrapolation  4 yields M. Botje, Rencontres de Moriond on QCD, March 2004

  9. SMES: statistical model of the early stage: Gazdzicki & Gorenstein, Acta Phys. Pol. B30(1999)2705) (pion yield is measure of entropy) Energy dependence of  yields • Increase of w with energy gets steeper at the SPS • Increase of slope by about a factor of 1.3 • Increase of initial # d.o.f (g) by 1.34  3? M. Botje, Rencontres de Moriond on QCD, March 2004

  10. Monotonic increase of K–/– with a hint of structure at 30 AGeV • Sharp peak in K+/+ confirmed by the 20 and 30 AGeV data • K+/+ constant between 158 AGeV and RHIC Energy dependence of kaon yields P+P M. Botje, Rencontres de Moriond on QCD, March 2004

  11. Hadrochemical freezeout params close to phase boundary at SPS Statistical hadron-gas model Assume hadron species populated according to phase space (Fermi, Hagedorn): extract T and B at chemical freeze-out from fits to all particle yields (Beccattini PRC 69(2004)024905) Dashed line: smooth interpolation of freeze-out curve (Cleymans and Redlich PRL 81(1998)5284) Phase boundary: estimate by Fodor and Katz JHEP 203(2002)14 M. Botje, Rencontres de Moriond on QCD, March 2004

  12. Hadron-gas model: K/ ratios • Interplay between T and B leads to weak maximum in K+/+ • Model captures the trend (by construction) but fails to describe sharp peak in the K+/+ ratio M. Botje, Rencontres de Moriond on QCD, March 2004

  13. Y = L, X-, W-+W+ x 6 x 15 Energy dependence of hyperon production 4p yields  @ 30, 40, 80, 158 AGeV   @ 40, 158 AGeV x6 • Ls show a distinct maximum at 30AGeV • Weak maximum for Xs and Ws Hadron-gas model: Braun-Munzinger, Cleymans, Öschler, Redlich Nucl. Phys. A697 (2002) 902 M. Botje, Rencontres de Moriond on QCD, March 2004

  14. Both UrQMD and HMD fail to describe the sharp maximum in the K+/+ ratio Comparison to hadron-string models HSD UrQMD From Bratkovskaya et al, nucl-th/0401031 M. Botje, Rencontres de Moriond on QCD, March 2004

  15. SMES: SMES prediction (Gazdzicki, Gorenstein: Acta Phys. Pol. B30(1999)2705) mixed hadronic • Hadronic phase: Es rises rapidly with temperature • Partonic phase: Es 0.21 independent of T • Peak in Es reflects phase transition in the model partonic M. Botje, Rencontres de Moriond on QCD, March 2004

  16. Comparison of models Data presently favour the SMES Onset of deconfinement at the SPS? Challenge to model builders: Can observed anomalous energy dependence be accomodated in a hadronic scenario? M. Botje, Rencontres de Moriond on QCD, March 2004

  17. Conclusion from the SPS energy scan • Anomalies observed in central Pb+Pb collisions • steepening rate of increase of pion production • sharp peak in the strange particle to pion ratio • constant slopes of the K+ and K– mT spectra • Present models without deconfinement in the early phase do not reproduce the details of the energy dependence • Phase transition scenario in Statistical Model of the Early stage is compatible with the data M. Botje, Rencontres de Moriond on QCD, March 2004

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