1 / 32

NA57 Results

NA57 Results. R. Lietava The University of Birmingham, UK For the NA57 Collaboration. Content. Introduction Enhancement at 40 and 160 GeV Transverse mass spectra -> transverse dynamics Rapidity spectra -> longitudinal dynamics Nuclear modification factors at 160 GeV Summary.

khanh
Download Presentation

NA57 Results

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NA57 Results R. Lietava The University of Birmingham, UK For the NA57 Collaboration ISMD 2005

  2. Content • Introduction • Enhancement at 40 and 160 GeV • Transverse mass spectra -> transverse dynamics • Rapidity spectra -> longitudinal dynamics • Nuclear modification factors at 160 GeV • Summary ISMD 2005

  3. NA57 experiment 5 cm 5 cm 30 cm L p- X- decay vertices B • NA57 studies the production of strange • and multi-strange baryons in heavy ion • interactions as a function of • collision centrality • collision energy 1M channels Silicon telescope W- L + K-( BR = 67.8 % ) X- L + p- ( BR = 99.9 % ) L p- + p( BR = 63.9 % ) K0 p+ + p-( BR = 68.6 % ) s target ISMD 2005

  4. Determinedfromcharged particle multiplicity measured in a dedicated Si-strips detector Npartand Ncollfrom trigger cross section (Glauber + WNM calculations) trigger 60% of Pb-Pb inel (7.26 b) Centrality of the collisions Pb-Pb 160 A GeV 0 1 2 3 4 Nch ISMD 2005

  5. Yields and enhancements • Doubledifferential cross section for each particle fitted to: • assuming flat/gaussian rapidity distribution in the selected acceptance. • Inverse slope of mT distribution ( T = Tapp ) free parameter of the fit. • Yield(average particle multiplicity per event) • extrapolated to a common • y-pT region: • Strangeness enhancement: ISMD 2005

  6. Hyperon enhancements at 160 A GeV/c _ • Significant centrality dependence of strangeness enhancements for all hyperons except for L systematic errors: 10% for L, X 15% for W Most peripheral class: <Nwound> = 62  4 [ ] ISMD 2005

  7. Hyperon enhancements at 40 A GeV/c Most peripheral class: <Nwound> = 57  4 (95 % confidence level) • Enhancements still there at 40 A GeV with the same hierarchy as for higher energy data:E(L) < E(X) ISMD 2005

  8. Energy dependence of hyperon enhancements • steeperincrease with centrality at lower energy • enhancements in the most central collisions (classes 3-4) are larger at 40 GeV than at 160 GeV ISMD 2005

  9. Transverse mass spectra Hydro picture: mT spectra sensitive to the transverse flow Blast wave description of the spectra: Uniform particle density Ref: E Schnedermann, J Sollfrank and U Heinz, Phys. Rev. C48 (1993) 2462 NA57 papers: F. Antinori et al J. Phys. G: Nucl. Part. Phys. 30 (2004) 823 G.E. Bruno et al J. Phys. G: Nucl. Part. Phys. 31 (2005) S127 ISMD 2005

  10. Blast-wave fit to mT spectra T = 144 ± 7(stat) ± 14(syst) MeV <b> = 0.381 ±0.013(stat) ± 0.012(syst) +11 - 10 T = 118 ± 5(stat) (syst) MeV +0.011 - 0.013 <b> = 0.398 ± 0.010(stat) (syst) Pb-Pb 160 A GeV/c Pb-Pb 40 A GeV/c • Thermal freeze-out temperature lower at 40 A GeV/c • Similar transverse flow ISMD 2005

  11. Centrality dependence of the freeze-out parameters Pb-Pb 160 A GeV/c Pb-Pb 40 A GeV/c With increasing centrality: • Transverse flow velocity increases • Freeze-out temperature decreases ISMD 2005

  12. K0 and L deviate • significantly • from flatness • in our • limited acceptance • No centrality • dependence Rapidity distributions in Pb-Pb at 160 A GeV/c ISMD 2005

  13. Longitudinal dynamics thermal model thermal model with longitudinal flow (Bjorken) • Tf fixed to 143 MeV (from blast-wave) • < L > = 0.42 ± 0.03 c • 2/ndf = 28.2 / 32 ISMD 2005

  14. Central to peripheral nuclear modification factor at sNN=17.3 GeV(i.e. beam momentum = 158 A GeV/c) where “C” and “P” are two centrality classes, in general Central and Peripheral F. Antinori et al Phys. Lett. B in press, preprint nucl-ex/0507012 “Central-to-peripheral nuclear modification factors in Pb-Pb collisions at sNN = 17.3 GeV” ISMD 2005

  15. Nuclear modification factors Binary scaling Scaling with Npart ISMD 2005

  16. RCP Comparisons STAR vs NA57 • RCP at SPS >RCP at RHIC • Relative pattern similar at SPS and RHIC STAR, PRL92 (2004) 052302 WA98 vs NA57 • For pt < 1.5 GeV (h-  -): 0 and h- compatible • For pt > 1.5 GeV (h-  K-, p): RCP for K0 and h- > RCP for 0 WA98, EPJC23 (2002) 225 ISMD 2005

  17. Summary • Strangeness enhancements measured at 40 GeV/c with the same hierarchy as at 160 GeV/c • Blast wave analysis of transverse and longitudinal spectra: • Centrality dependence of freeze out temperature and expanding velocity observed at both energies • < L >  <  > • Nuclear modification factor Rcp: • Similar pattern as at RHIC, lower in magnitude • Interpretation: initial state effect (PDF) versus final state effect (parton energy loss,recombination)  systematic theoretical study required ISMD 2005

  18. Back up slides ISMD 2005

  19. CERN Paris - CdF , Strasbourg Prague Athens Utrecht NA57 Bergen, Oslo St. Petersburg Bratislava, Košice Birmingham Bari, Catania, Padua, Rome, Salerno

  20. The NA57 Collaboration ISMD 2005

  21. Layout of the NA57 experiment at CERN SPS Target: 1% Pb , 8% Be Scintillator Petals: centrality trigger MSD: Multiplicity Silicon Detector Tracking device: silicon pixel planes (5 x 5 cm2 ) pixel size: 50500 m2 Lever arm: pixel planes & double side mstrips Pb-Pb only 1M channels ISMD 2005

  22. Centrality of the collision Pb-Pb 160 A GeV 0 1 2 3 4 Nch Centrality determination - from charged particle multiplicity measurement Nwound - from trigger cross section (Glauber model calculations) ISMD 2005

  23. Acceptance windows in Pb-Pb at 158 A GeV/c ISMD 2005

  24. Sample invariant mass spectra L X- W- L X+ W+ Residual combinatorial background (few %) subtracted or included in the systematics ISMD 2005

  25. Data corrected for acceptance and also for detector and reconstruction efficiency by Monte Carlo simulation In the acceptance window: Yield (i.e. particle per event) Transverse mass spectra (Tapp) Extrapolation to a common window: one unit of rapidity about ycm full range of pT Hyperon yield measurements ISMD 2005

  26. Enhancements w.r.t. number of binary collisions at 160 A GeV/c Enhancement = <Yield> / <Nbin> 10 10 (<Yield> / <Nbin>)p-Be <Nbin> 1 1 • Going from p-Be to Pb-Pb X and W yields scale • faster than <Nbin> ISMD 2005

  27. Centrality dependence (i) No centrality dependence in our limited acceptance ISMD 2005

  28. Centrality dependence (ii) No centrality dependence in our limited acceptance ISMD 2005

  29. Full collected statistics (two years of data taking in nice agreement) New centrality classes Rcp for unweighted spectra Dedicated analysis for particle selection at high pT Residual combinatorials estimated with event mixing and subtracted Paper submitted to PLB and soon available as pre-print Few details about the analysis ISMD 2005

  30. Comparisons with theoretical pre-dictions • X N Wang: perturbative-QCD-based calculation with and without in-medium parton energy loss • Initial dNg/dy scaled down from RHIC according to the observed decrease in dNch/dy ( factor 2) • Initial-state partonic kT broadening tuned on the original Cronin effect data • Cross-checked using different model: PQM (BDMPS-based) • medium density determined from RHIC data and extrapolated down to SPS energy; Cronin enhancement included Ref: Dainese, Loizides, Paic, EPJC38 (2005) 495; private communication Ref: X N Wang PRC 68 (2001) 064910; PLB 595 (2004) 165; private communication

  31. For NA49:K0 = 0.5*(K++K-) s Comparison NA57-NA49 Particle yields per participant Similar centrality regions: • about 30% systematics on the absolute value of the • yields (under investigation) but … *Refs: Physical Review C 66, 054902 (2002), arXiv:nucl-ex/0311024, Phys. Lett. B 538 (2002), 275. ISMD 2005

  32. Comparison NA57-NA49 Particle ratios • … particle ratios compatible within errors (no impact on relative yields) *Refs: Physical Review C 66, 054902 (2002), arXiv:nucl-ex/0311024, arXiv:nucl-ex/0305021, arXiv:nucl-ex/0311029. ISMD 2005

More Related