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V. Friese v.friese@gsi.de

Indications of the Onset of Deconfinement at low SPS Energies Recent Results from NA49 ICPAQGP 5 , Colcatta, February 2005. V. Friese v.friese@gsi.de. for the collaboration. The NA49 Detector. Hadron spectrometer Large acceptance: 4 π yields PID by dE/dx and TOF

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V. Friese v.friese@gsi.de

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  1. Indications of the Onset of Deconfinementat low SPS EnergiesRecent Results from NA49ICPAQGP5, Colcatta, February 2005 V. Friese v.friese@gsi.de for the collaboration

  2. The NA49 Detector • Hadron spectrometer • Large acceptance: 4π yields • PID by dE/dx and TOF • Centrality by forward calorimeter Beam energies: 20, 30, 40, 80, 158 AGeV Systems: p+p, p+A, C+C, Si+Si, Pb+Pb V. Friese ICPAQGP, Colcatta, February 2005 2

  3. Midrapidity mt spectra (central Pb+Pb) Simultaneous blast wave fit constant βt π, d excluded from fit SSH, PRC 48 (1993) 2462 Single fireball model with common temperature and flow velocity works Beware: Resonance feeddown, velocity profile V. Friese ICPAQGP, Colcatta, February 2005 3

  4. NA49, nucl-ex/0409004 Early freeze out of Ω ? Linear velocity profile:Ω agrees better with charmonia than with other hadrons Indication for earlier freeze out? NA49, nucl-ex/0409004 (*) Gorenstein, Bugaev, Gadzicki, PRL 88 (2002) 132301 V. Friese ICPAQGP, Colcatta, February 2005 4

  5. Transverse spectra at lower energies 30 AGeV 20 AGeV Blast wave fits work at all SPS energies Kinetic freeze out: T = 120 – 130 MeV βt = 0.4 – 0.5 for constant βt V. Friese ICPAQGP, Colcatta, February 2005 5

  6. Kaon Slope Parameters Kaon spectra almost perfect exponential → fit dn/dmt~ mt e-mt/T Constant inverse slope at all SPS energies Constant temperature and pressure? Mixed phase? V. Friese ICPAQGP, Colcatta, February 2005 6

  7. Average mt Other particle types: No exponential spectrum → calculate mean mt Similar behaviour seen for pions; protons less conclusive V. Friese ICPAQGP, Colcatta, February 2005 7

  8. Clear hiearchy of rapidity widths at SPS: π- > K+ > K- > Λ exception: φ Longitudinal Distributions (central Pb+Pb) Gaussianlike rapidity spectra (except p, Λ) V. Friese ICPAQGP, Colcatta, February 2005 8

  9. Strange to Nonstrange Ratios: Kaons Sharp structure in K+ / π, not reproduced by hadronic models (Full equlibrium) hadron gas model overpredicts kaons at higher SPS energies V. Friese ICPAQGP, Colcatta, February 2005 9

  10. Strange to Nonstrange Ratios: Λ Similar structure seen as in K+(sharp peak at 30 AGeV) HGM describes overall structure, but location of peak different (?) UrQMD not far off (not shown) V. Friese ICPAQGP, Colcatta, February 2005 10

  11. Total Strangeness Peak at 30 AGeV,undersaturation at higher SPS energies Energy dependence changes at 30 AGeV V. Friese ICPAQGP, Colcatta, February 2005 11

  12. Ruling out hadronic equlibirium ? Features of HGM: • No sharp peak • Overprediction of strangeness yields at higher SPS energies • Maxima at different positions for K, Λ, Ξ, Ω If connected with PT, maxima should be at the same energy for all strange species Ξ at 20, 30 AGeV possibly discriminative → to come V. Friese ICPAQGP, Colcatta, February 2005 12

  13. … one more Parameter Becattini et al., PRC 69 (2004) 024905 Introducing γS < 1 gives better description of NA49 4π yieldsaround 30 AGeV: γS ≈ 1 At higher energies: γS ≈ 0.7what does it mean? V. Friese ICPAQGP, Colcatta, February 2005 13

  14. Indication for deconfinement PT ? Gazdzicki, Gorenstein, Act. Phys. Polon. B 30 (1999) 2705 Hama et al., Braz. J. Phys. 34 (2004) 322 Phase transition at 30 AGeV QGP + hadronic phases Features in strangeness / pion and kaon slopes can be obtained with models assuming a phase transition V. Friese ICPAQGP, Colcatta, February 2005 14

  15. NA49 NA49 preliminary preliminary Relative Strangeness Fluctuations Dynamical fluctuations in K/π increase towards low SPS energies Not reproduced in UrQMD p/π in agreement with hadronic transport (resonance decays) V. Friese ICPAQGP, Colcatta, February 2005 15

  16. Mean pt Fluctuations Measured at top SPS as function of system size Maximum at small Npart ( ≈ 100 ) But: similar pattern observed at RHIC Interesting: Measure at lower SPS energies (hint taken) V. Friese ICPAQGP, Colcatta, February 2005 16

  17.   Es System Size: Strangeness Enhancement NA49, 158 AGeV Tounsi, Redlich, JPG 28 (2002) 2095 Strangeness enhancement  canonical suppression Volume effect on strangeness conservation But: No quantitative agreement with data (rise too fast) if V ~ Npart Disagreement between peripheral Pb+Pb and central Si+Si, C+C V. Friese ICPAQGP, Colcatta, February 2005 17

  18. Cluster Ansatz bei C. Höhne Microscopic calculation of overlapping „strings“ (VENUS, UrQMD) → correlation volume as fct. of Npart Calculate ES~ η according to statistical model, taking into account the distribution in Vcorr Describes data perfectly ! Application to fluctuations? V. Friese ICPAQGP, Colcatta, February 2005 18

  19. Summary • Anomalies at lower SPS energies observed by NA49: • sharp peak in strange particles to pion ratio • constancy of kaon slopes • pion production rate increases (not discussed) • Fluctuation in K/π also increase towards low SPS energies, other signals less convincing / absent • Best explanation by scenario with onset of deconfinement • Low SPS is still interesting: • EoI to CERN for SPS running from 2009 on • Plans of fixed target experiments at RHIC • FAIR at GSI V. Friese ICPAQGP, Colcatta, February 2005 19

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