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NA57 main results

Comparison with NA49-NA45. NA57 main results. Giuseppe E Bruno Università di Bari and INFN - Italy. Prologue NA57 was the dedicated experiment at the SPS for the study of multi-strange particle production at midrapidity The analysis is essentially completed

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NA57 main results

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  1. Comparison with NA49-NA45 NA57 main results Giuseppe E Bruno Università di Bari and INFN - Italy • Prologue • NA57 was the dedicated experiment at the SPS for the study of multi-strange particle production at midrapidity • The analysis is essentially completed • In this talk we concentrate on the main contributions from NA57 Outline Introduction experimental technique Main results hyperon enhancements strange particle spectra nuclear modification factors (RCP) Conclusions

  2. 5 cm Silicon Pixel Telescope 5 cm p p- 30 cm L B p- X- Target Experimental technique • detect K0S, L, X and W by reconstructing weak decay topologies K0s--> p+ + p- BR = 69.2% L --> p + p- BR = 63.9% X---> L + p- BR = 99.9% W---> L + K-BR = 67.8% Giuseppe E Bruno

  3. Hyperon signals background unsubtracted 158 A GeV/c Pb-Pb 40 A GeV/c Pb-Pb Giuseppe E Bruno

  4. Centrality classes • Centrality determined from charged particle multiplicity (Nch) • Nwound , Nbin from Glauber model fit Pb-Pb 158 A GeV 0 1 2 3 4 NA57, J. Phys. G31 (2005) 321-335 Giuseppe E Bruno

  5. Comparison NA57-NA49-NA44dN/dy of K0s and ½(K++K-) ½(K++K-) NA49 0-5% scaled to 0-10% NA57 0-11% K0s NA49 0-10% NA45 0-7% scaled to 0-10% NA49 Nucl. Phys. A715 (2003) 453c, QM2002 NA57 Jour. Phys. G 31 (2005) 1345-1357 NA49 Phys. Rev. C 66, 054902 (2002) NA45 S. Radomski Ph.D. thesis Giuseppe E Bruno

  6. hyperon enhancements • confirmation of hyperon enhancements • centrality dependence • energy dependence Giuseppe E Bruno

  7. Two historic QGP predictions • restoration of csymmetry -> increased production of s • mass of strange quark in QGP expected to go back to current value • ms ~ 150 MeV ~ Tc • copious production of ss pairs, mostly by gg fusion [Rafelski: Phys. Rep. 88 (1982) 331] [Rafelski-Müller: P. R. Lett. 48 (1982) 1066] • deconfinement  stronger effect for multi-strange • can be built using uncorrelated s quarks produced in independent microscopic reactions • strangeness enhancement increasing with strangeness content [Koch, Müller & Rafelski: Phys. Rep. 142 (1986) 167] Giuseppe E Bruno

  8. Errors: systematic statistical 3 2 10 10 Hierarchy of the enhancements with strangeness content (QGP prediction) 2 1 1 1 1 1 10 100 1000 1 10 100 1000 Enhancements at 158 GeV SE • hadronic transport models cannot reproduce this <Nwound> <Nwound> Giuseppe E Bruno

  9. Canonical Suppression (Hamieh et al.) Centrality dependence • enhancement still large around NW = 50 • enhancing mechanism still effective at 25 + 25 ! • effect increases with centrality (except L) • enhancing mechanism more and more effective as NW increases • constrain models ! e.g.: “canonical suppression model” predicts quick saturation of effect with centrality, at odds with data [Hamieh et al.: Phys. Lett. B486 (2000) 61] Giuseppe E Bruno

  10. (95 % confidence level) Hyperon enhancements at 40 GeV • The effect is still present • enhancing mechanism already effective at low energy Giuseppe E Bruno

  11. 10 10 1 1 Energy dependenceof hyperon enhancements • roughly same order of magnitude as at 158 GeV • steeper centrality dependence • slightly larger than at 158 GeV for most central collisions • energy dep. of enhancements not yet understood theoretically Giuseppe E Bruno

  12. Redlich et al., JPG28 (2002) 2095 X- 40 GeV 10 158 GeV 1 • energy dependence also constrains models • e.g. much weaker than predicted by canonical suppression model: Giuseppe E Bruno

  13. NA49 (√sNN=17.3GeV) L sensitive to baryon density? NA49, nucl-ex 0701042 (2007), JPG in print Other measurements of SE STAR(√sNN=200GeV) full symbols versus NA57(√sNN=17.3GeV) open symbols • SE at RHIC... ... similar effect as at SPS STAR, nucl-ex 07052511 (2007), submitted to PRL Giuseppe E Bruno

  14. 2. strange particle spectra • centrality dependence of • freeze-out temperature T • radial expansion bT Giuseppe E Bruno

  15. Blast wave model • mT distributions described as combined result of thermal motion (T) and collective transverse expansion (bT) at freeze-out Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462 • for most central (5%) collisions: T ~ 120 MeV, bT ~ .45 • confirmation of NA49 results NA57, JPG 30(2004) 823 Giuseppe E Bruno

  16. NA57: spectra vs centrality NA57 JPG 30(2004) 823 Giuseppe E Bruno

  17. peripheral 23-40% 40-53% 11-23% 4.5-11% 0-4.5% central 158 A GeV/c Blast wave vs centrality NA57 158 GeV Centrality classes: • 0  40 to 53 % most central • 1  23 to 40 % most central • 2  11 to 23 % most central • 3  4.5 to 11 % most central • 4  4.5 % most central • For more peripheral: • Transverse flow velocity decreases • Freeze-out temperature increases  fix hydro parameters NA57, JPG 30(2004) 823 Giuseppe E Bruno

  18. 1s contours n=1 v2 vs hydro at SPS? • v2 not at hydro limit? • v2 well below hydro limit for Tf = 120 MeV • but NA57: Tf increases for peripheral events [Snellings et al.: nucl-ex/0305001] • Tf = 146 ± 17 MeV for (11-23)% centrality; NA45 data (13-26)% • so hydro limit perhaps not too far... [NA45: Phys. Rev. Lett. 92 (2004) 032301] Giuseppe E Bruno

  19. 3. nuclear modification factors (RCP) • direct comparison to RHIC high pT quenching results Giuseppe E Bruno

  20. Rcp at RHIC • high pT: suppression • interpreted as due to jet quenching • medium pT: meson/baryon effect • valence quark recombination? Giuseppe E Bruno

  21. RCP in NA57 • bars = quadratic sum of stat. and pT-dependent systematic errors • no evidence for high pT suppression (RCP < 1) • but similar relative K0S/L pattern as at RHIC NA57, PLB 623(2005) 17 STAR, PRL92 (2004) 052302 Giuseppe E Bruno

  22. Comparisons to models • Comparison to K0S calculations (X.N. Wang; PQM) • medium density extrapolated down from RHIC according to multiplicity • Cronin effect included • better agreement with E loss X.N.Wang, PRC68 (2001) 064910; PRL81 (1998) 2655; PLB595 (2004) 165 + private comm. PQM: Dainese, Loizides, Paic, EPJC38 (2005) 495 + private comm.

  23. Relative L, K0S pattern • Very similar at SPS and RHIC NA57, PLB 623(2005) 17 STAR, PRL92 (2004) 052302

  24. Conclusions • Hyperon enhancements • confirmation of enhancement for central colls • centrality dependence: effect already present at ≈ 25+25 participants • energy dependence: similar effects at √sNN=8.8, 17.3 (and 200) GeV • Strange particle mt spectra • centrality dependence of kinetic freeze-out parameters • Nuclear modification factor Rcp • similar relative L/K0s pattern as at RHIC Giuseppe E Bruno

  25. of course we did more … That's not all folks Giuseppe E Bruno

  26. NA57 publications in refereed journals • Study of the transverse mass spectra of strange particles in Pb-Pb collisions at 158 A GeV/c J. Phys. G 30 (2004) 823-840 • Energy dependence of hyperon production in nucleus-nucleus collisions at SPS Phys. Lett. B595 (2004) 68-74 • Multiplicity of charged particles in Pb-Pb collisions at SPS energies J. Phys. G31 (2005) 321-335 • Central-to-peripheral nuclear modification factors in Pb-Pb collisions at √ sNN = 17.3 GeV/c Phys. Lett. B 623 (2005) 17-25 • Rapidity distributions around mid-rapidity of strange particles in Pb-Pb collisions at 158 A GeV/c J. Phys. G 31 (2005) 1345-1357 • Enhancement of hyperon production at central rapidity in 158 A GeV/c Pb-Pb collisions J. Phys. G 32 (2006) 427-441 • Transverse dynamics of Pb-Pb collisions at 40 A GeV/c viewed by strange hadrons J. Phys. G 32 (2006) 2065-2080 • Expansion dynamics of Pb-Pb collisions at 40 A GeV/c viewed by negatively charged hadrons J. Phys. G 34 (2007) 403-429 Giuseppe E Bruno

  27. The NA57 Collaboration F. Antinorik,P.A. Bacone,A. Badalàf, R. Barberaf,A. Belogiannia,I.J. Bloodworthe,M. Bombarah,G.E. Brunob,S.A. Bulle,R. Caliandrob,M. Campbellg, W. Carenag, N. Carrerg,R.F. Clarkee,A. Dainesek,D. Di Barib,S. Di Liberton,R. Diviàg,D. Eliab,D. Evanse,G.A. Feofilovp,R.A. Finib,P. Ganotia,B. Ghidinib,G. Grellao,H. Helstrupd, K.F. Hetlandd,A.K. Holmej,A. Jacholkowskif, G.T. Jonese, P. Jovanovice, A. Juskoe,R. Kamermansr,J.B. Kinsone,K. Knudsong,V. Kondratievp,I. Králikh,A. Kravčákovái,P. Kuijerr,V. Lentib,R. Lietavae,G. Løvhøidenj,V. Manzarib,M.A. Mazzonin,F. Meddin,A. Michalonq,M. Morandok,P.I. Normane,A. Palmerif, G.S. Pappalardof,B. Pastirčákh,R.J. Platte,E. Quercighk,F. Riggif,D. Röhrichc,G. Romanoo, R. Romitab, K. Šafaříkg,L. Šándorh,E. Schillingsr,G. Segatok,M. Senél, R. Senél,W. Snoeysg, F. Soramelk,M. Spyropoulou-Stassinakia,P. Starobam,R. Turrisik,T.S. Tveterj,J. Urbáni,P. van de Venr,P. Vande Vyvreg, A. Vascottog,T. Vikj,O. Villalobos Bailliee,L. Vinogradovp,T. Virgilio,M.F. Votrubae,J. Vrlakovai,P. Závadam. a: Athens, b: Bari,c: Bergen,d: Bergen,e: Birmingham,f: Catania,g: CERN,h: Kosice,i: Kosice,j: Oslo,k: Padova,l: Collège de France,m: Prague, n: Rome,o: Salerno,p: St. Petersburg,q: Strasbourg,r: Utrecht Giuseppe E Bruno

  28. The NA57 Collaboration Prague CERN Athens Paris - CdF , Strasbourg Bari, Catania, Padua, Rome, Salerno Utrecht Bergen, Oslo St. Petersburg Bratislava, Košice Birmingham Giuseppe E BrunoG.E. BRUNO - NA57

  29. Experimental apparatus Target: 1% Pb Scintillator Petals: centrality trigger MSD: Multiplicity Silicon Detector Tracking device: silicon pixel planes (5 x 5 cm2 ) Lever arm: double-sided mstrips Giuseppe E Bruno

  30. Strange Particle reconstruction in NA57 • Decay channels: plus c.c. for anti-hyperons • Interactions: • Pb-Pb, p-Be, p-Pb @ p= 158A GeV/c • Pb-Pb, p-Be @ p= 40A GeV/c • Acceptance • Dy  1 around mid-rapidity • pT > 0.5 GeV/c

  31. 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 Giuseppe E Bruno

  32. 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 but … *Refs: Physical Review C 66, 054902 (2002), Phys.Rev.Lett. 93 (2004) 022302, Phys. Lett. B 538 (2002), 275.

  33. Comparison NA57-NA49 Particle ratios • … particle ratios compatible within errors (no impact on relative yields) *Refs: Physical Review C 66, 054902 (2002), Phys.Rev.Lett. 93 (2004) 022302, arXiv:nucl-ex/0305021, arXiv:nucl-ex/0311029.

  34. Comparison NA57-NA49dN/dy • Different acceptances: • NA57: ~ |y-ycm| < 0.5 • NA49: ~ |y-ycm| < 1.5 NA49, PRL93 (2004) 022302; PRC66 (2002) 054902; PLB538 (2002) 275; nucl-ex/0409004

  35. Comparison NA57-NA49dN/dy of K0s NA57 0-11% NA49 0-10% NA49, Nucl. Phys. A715 (2003) 453c, QM2002 Giuseppe E Bruno

  36. Comparison NA57-NA49-NA44dN/dy of K0s and ½(K++K-) ½(K++K-) NA49 0-5% scaled to 0-10% NA57 0-11% K0s NA49 0-10% NA45 0-7% scaled to 0-10% NA49 Nucl. Phys. A715 (2003) 453c, QM2002 NA57 Jour. Phys. G 31 (2005) 1345-1357 NA49 Phys. Rev. C 66, 054902 (2002) NA45 S. Radomski Ph.D. thesis Giuseppe E Bruno

  37. 30 K+ 20 NA57 0-5% Statistical errror Systematic errror 10 NA49 0-5% K- 15 10 5 Comparison NA57-NA49dN/dy of K0s vs. ½(K++K-) NA49 Physical Review C 66, 054902 (2002) Fit function: Giuseppe E Bruno

  38. Comparison NA57-NA49Yield/Nwound of L Giuseppe E Bruno

  39. Systematic errror Statistical errror Dy=1 Longitudinal dynamics Yield 0-53%sinel • Rapidity distributions (at central rapidity) for all levels of strangeness • Only K0s and L non-flat within acceptance Giuseppe E Bruno

  40. Longitudinal dynamics • thermal modelwithout flow • Thermal model+ Longitudinal flow (Bjorken) using T kin.f.out from Blast wave fit: • <bL> ~ 0.4 ~ <b> • almost isotropic expansion? Giuseppe E Bruno

  41. Centrality dependence (i) Giuseppe E Bruno

  42. Centrality dependence (ii) No centrality dependence in our limited acceptance Giuseppe E Bruno

  43. Yields and enhancements Cross section for each particle fitted to f(y) flat/Gaussian (for K0 and antilambda) Yield extrapolated to common y/pT region Strangeness enhancement PbPb relative to p-Be Giuseppe E Bruno

  44. Errors: systematic statistical 3 Enhancement = 2 10 10 Hierarchy of the enhancements with strangeness content (QGP prediction) <Yield> / <Nwound> 2 1 (<Yield> / <Nwound>)p-Be 1 1 1 No enhancement <Nwound> Particles having quarks in common with the nucleon Particles made up of newly created quarks only 1 10 100 1000 1 10 100 1000 Enhancements at 158 (√sNN=17.3) GeV Factor 20 for  • Hierarchical enhancement according to strangeness content • QGP prediction*: easier to build X and W by recombination • Significant centrality dependence, except for L Giuseppe E Bruno * Rafelski and Muller

  45. Enhancement = <Yield> / <Nbin> 10 10 (<Yield> / <Nbin>)p-Be <Nbin> 1 1 Enhancements w.r.t. number of binary collisions at 158 A GeV/c, i.e.pt-integrated RAA • Going from p-Be to Pb-Pb X and W yields scale • faster than <Nbin> Giuseppe E Bruno

  46. Ratios of Enhancements40 GeV/c / 160 GeV/c Giuseppe E Bruno

  47. A. Andronic et al. Nucl.Phys. A772 (2006) 167-199 A parenthesis: canonical aspects of strangeness enhancement • Thermal fits in HI work very well: • relative particle abundances ~ as expected at thermodynamical equilibrium for grand-canonical system, even for rare, multi-strange particles E.g. Giuseppe E Bruno

  48. √sNN=130GeV √sNN=8.8GeV 10 100 A parenthesis: canonical aspects of strangeness enhancement • Canonical vs Grand Canonical: energy penalty to create a strange particle • Canonical: computed taking into account also energy to create companion to ensure conservation of strangeness • Grand Canonical limit: just due to creation of particle itself. The rest of the system acts as a reservoir and “picks up the slack” • removal of canonical suppression* • increases with strangeness • detailed centrality dependence not reproduced (very crude modelling) • decrease of enhancements with √sNN predicted, but ~ order of magnitude close Giuseppe E Bruno *Tounsi, Redlich et al.

  49. Does this explain the observed enhancements ? A parenthesis: canonical aspects of strangeness enhancement • a system in eq., if it is large enough, is in GC eq., but being large in itself is not a sufficient condition for being GC! • if AA colls. were just a superposition of pp, they would have to be treated canonically all the same! • the system must also know it is large... • it must know that an Ω+ generated here can be compensated by, say, an Ω- on the other side of the fireball! • what counts is the correlation volume • how does the system know it is large? how can information travel so quickly through the system? • not by conventional hadronic transport (no time!) • natural if the system is coming back from deconfinement Giuseppe E Bruno

  50. Expansion dynamics viewed by negatively charged hadrons • Ref: Expansion dynamics of Pb–Pb collisions at 40 A GeV/c viewed by negatively charged hadrons, J. Phys. G 34 (2007) 403-429 HBT blast of strange dN/dmt Giuseppe E Bruno

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