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Strange Probes of QCD Matter

Strange Probes of QCD Matter. Huan Zhong Huang Department of Physics and Astronomy University of California Los Angeles, CA 90095-1547 Oct 6-10, 2008; SQM2008 Beijing. Thanks to Jinhui Chen, Gang Wang and Shingo Sakai. Outline. Strangeness in Bulk Partonic Matter

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Strange Probes of QCD Matter

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  1. Strange Probes of QCD Matter Huan Zhong Huang Department of Physics and Astronomy University of California Los Angeles, CA 90095-1547 Oct 6-10, 2008; SQM2008 Beijing Thanks to Jinhui Chen, Gang Wang and Shingo Sakai

  2. Outline • Strangeness in Bulk Partonic Matter • Hadronization and Evolution Dynamics • Thermalized Effective Quarks • PT Scale for Jet Energy Loss in QCD Medium • Is There a Clear Path-Length Effect in Eloss? • Ourlook

  3. Strangeness Probes Thermal Gluons of QGP QGP Thermal Gluons  effective strangeness production process P.Koch, B. Muller and J. Rafelski: Phys.Rept.142:167-262,1986 In central A+A collisions, there is no phase space penalty for being strange ! Au+Au@200GeV STAR Phys. Rev. Lett. 98 (2007) 62301 There is a penalty for being heavy – exp(-m/T) !

  4. Strangeness is Enhanced in A+A Collisions STAR Preliminary (Cu+Cu 200 GeV) Or Canonically Suppressed? 200 GeV Au+Au Data: Phys. Rev. C 77 (2008) 44908

  5. Strangeness enhancement: yield relative to p+p -meson enhancement: -- between K/L and X -- 200 GeV data > 62.4 GeV, unlike hyperons -- could not be solely due to the canonical suppression, there could be dynamics effect See Bedanga Mohanty’s Talk STAR Preliminary Strangeness enhancement X K, L 200 GeV 62.4 GeV

  6. Hadronization of Bulk Partonic Matter  Coalescence Partons at hadronization have a v2  Collectivity Deconfinement ! Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Rafelski+Danos, Molnar+Voloshin …..) Quark Recombination – (R.J. Fries et al, R. Hwa et al)

  7. Is KET better variable capturing the physical picture? Phenix: PRL 98, 162301 (2007) Empirically, maybe ! But why should it work for pions  mostly from decays why KET  not really additive !

  8. W and f particles are special ! Little resonance decay contribution ! Coalescence of thermal strange quarks --- important in A+A collisions ! What is the thermal quark pT distribution ? In the hydro region – coalescence of quarks with hydro expansion OR fragmentation of quarks Au+Au@200GeV Cu+Cu@200GeV

  9. Parton PT Distributions at Hadronization If baryons of pT are mostly formed from coalescence of partons at pT/3 and mesons of pT are mostly formed from coalescence of partons at pT/2 • and f particles have no decay feeddown contribution ! • decay contribution is small These particles have small hadronic rescattering cross sections 9

  10. Strange and down quark distributions s distribution harder than d distribution perhaps related to different s and d quarks in partonic evolution Independent Test – f/s should be consistent with s quark distribution Yes ! 10 See Jinhui Chen’s talk

  11. pT Scales and Physical Processes RCP Three PT Regions: -- Fragmentation -- multi-parton dynamics (recombination or coalescence or …) -- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )

  12. Hydrodynamics and Coalescence Most Hydrodynamic Calculations – Cooper-Frye Freeze-out thermal statistical distribution in the co-moving frame Coalescence model – has been applied to particles with pT > 2 GeV/c or so ! For pT < 2 GeV/c  hydrodynamic behavior OR coalescence of effective constituent quarks with radial flow are these approaches equivalent ? Empirically the coalescence physical picture appealing ! Problem: -- how to deal with resonances, r w effective mass of quarks ?

  13. RAA(pT>6GeV/c) Almost pT Independent RAA=(Au+Au)/[Nbinaryx(p+p)] Empirical Implications for a constant RAA for pT > 6 GeV/c !!

  14. Energy Loss Shifts pp pT to AA pT by DpT pp AA/Nbin DpT pT > 5 GeV/c For a power-law function (1+pT/a)-n a flat RAA DpT/pT constant ! What Physical Processes?

  15. Npart Dependence of Energy Loss No significant difference in DpT/pT between light hadron and non-photonic electrons ! DpT/pT ~ 25% in most central collisions ! The physical origin of the N2/3 dependence? Linear Npart not bad either

  16. Absence of Explicit Path Length Dependence The centrality dependence of DpT/pTcould be due to the initial energy density in collisions !

  17. T. Hirano et al, Phys. Rev. C69, 034908 (2004) What Possible Physical Scenario for ELoss without L dependence ELoss of Partons: 1) Strong dependence on energy density 2) Rapid decrease of energy density in time interval < traversing time Hydrodynamic models show such a scenario plausible !

  18. Path-Length Dependence in Soft Particles 3<pTtrig<4GeV/c & 1.0<pTasso<1.5GeV/c 20-60% STAR  = associate - trigger (rad) At low pT region, the medium response to Parton ELoss -- has path-length dependence Caution: the current trigger pT is high enough to be in the dominant parton energy loss domain !

  19. V2 and RAA are Related via Path Length Dependence Precise value of v2 at pT > 6, 10 GeV/c ? RAA at pT > 10 GeV/c at RHIC should RAA approach unity at higher pT ? Future measurements will shed lights on possible physical scenarios for parton energy loss dynamics ! Heavy Quarks will be special -- Lorentz g dependence on parton ELoss on jet-medium interaction Mach cone formation?

  20. Summary Central Au+Au Collisions at RHIC Bulk Partonic Matter -- 1) strangeness equilibrated 2) parton collectivity v2 and hydro expansion 3) multi-parton dynamics coalescence/ recombination 4) pT or KET distributions for effective quarks L X W

  21. Summary Parton Energy Loss  Hadron PT Scale > 5-6 GeV/c Constant RAA  DpT /pT constant as a function of pT Absence of Clear Path-Length Dependence of ELoss -- Rapid Decrease of Energy Density with Evolution Time -- Even partons originated from the center of the hot/dense fireball may escape Theoretically Eloss calculations – dynamic issue simultaneous calculation of RAA and v2 at high pT !!

  22. Eloss ~ L*Density ?

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