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 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

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) !

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

Strangeness enhancement STAR Preliminary 62.4 GeV 200 GeV X K, L 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

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)

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 !

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 Cu+Cu@200GeV Au+Au@200GeV

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

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

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? )

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 ?

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

Energy Loss Shifts pp pT to AA pT by DpT 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?

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

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

What Possible Physical Scenario for ELoss without L dependence T. Hirano et al, Phys. Rev. C69, 034908 (2004) 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 !

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 !

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?

Summary L X W 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 W X L

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 !!

Eloss ~ L*Density ?