Xi’an 2006 STAR 1 STAR Particle Ratios and Spectra: Energy and  B dependence International Workshop On Hadron Physics and Property of High Baryon Density Matter Olga Barannikova, UIC

Xi’an 2006 STAR 2 Outline:  Identified measurements in STAR  QCD Phase Diagram Theoretical view Experimental probes: AGS, SPS, RHIC  Excitation functions for yields and ratios  Freeze-out properties in AA collisions Exploring the QCD phases  Search for (tri)critical point  Probing Medium Hadronization mechanisms Energy Loss  Summary Soft Hard

Xi’an 2006 STAR 3 Particle Identification  Topological method dE/dx method K(892)   + K  (1020)  K + K  (1520)  p + K... K 0 s   +     + p   +    TPC NIM A 499, 659 (2003)NIM A 508, 181 (2003)  K p e  d He3 TOF

Xi’an 2006 STAR 4 Transverse mass spectra Variety of hadron species: , p,             Au+Au, Cu+Cu, d+Au, pp Same experimental setup! Spectral shapes: kinetic FO properties transverse radial flow Flavor composition: Hadro -chemistry chemical FO properties T chemical FO strangeness production  PRL 97, (2006) nucl-ex/ nucl-ex/

Xi’an 2006 STAR 5 QCD Phase Diagram Lattice QCD prediction F. Karsch, hep-lat/ (2004) T C ~170  8 MeV  C ~0.5 GeV/fm 3 E SC  u =  d = 0,  s =  The chiral phase transition changes from second to first order at a tricritical point; SC  s >>  u =  d  0 Presence of the strange quark shifts E to the left; CFL E  u =  d  0,  s =  2 nd order phase transition changes into smooth cross-over

Xi’an 2006 STAR 6 Theory: NJL/I Asakawa,Yazaki ’89 NJL/II ibidem COBarducci, et al. ’89-94 NJL/instBerges, Rajagopal ’98 RMHalasz, et al. ’98 LSM Scavenius, et al. ’01 NJL ibidem LR-1 Fodor, Katz ’01 CJT Hatta, Ikeda, ’02 HB Antoniou, Kapoyannis ’02 LTE Ejiri, et al. ’03 LR-2 Fodor, Katz ’04 — MIT Bag/QGP (only 1st order) Theoretical (models and lattice) predictions for the location of the critical point. M. Stephanov Acta Phys.Polon.B35: ,2004 Where is the Critical Point?

Xi’an 2006 STAR 7 Particle Yields and Statistical Models Thermalized system of hadrons can be described by statistical model: Hadron species are populated according to phase space probabilities (maximum entropy) (Fermi, Hagedorn) Very successful in describing experimental data T, μ q, μ s,V, γ s,… Mapping the Phase Diagram T chem Schematic space–time view of a heavy ion collision Experiment:

Xi’an 2006 STAR 8 Model Description of Yields STAR white paper NuclPhysA757(05)102 T=160  5 MeV  B =24  4MeV  s =0.99  0.07  2 =9.6/8 dof

Xi’an 2006 STAR 9  B drops with collision energy G. Roland From calculations by Redlich et al, Becattini et al, Braun- Munzinger et al, Rafelski et al. Baryon transport at mid-rapidity: Smooth excitation function AGS  RHIC Similar trend for between AA and pp Systematics of Thermal Freeze-out Satz: Nucl.Phys. A715 (2003) 3c filled: AA open: elementary T ch approaches limiting value Can saturation trend be explained by Hagedorn hypotheses?

Xi’an 2006 STAR 10  Chemical Equilibrium:  s  1  s ~ u, d  T, µ B,V - vary with energy, but Λ, Ξ - yields stays constant  Change in baryon transport reflected in anti-baryons (and K) Strangeness Production PRL 89 (2002), nucl-ex/ nucl-ex/ H.Caines Npart ss P. Steinberg et al.. 0

Xi’an 2006 STAR 11 Phase Diagram 1st order QGP Hadronic phase Cleymans and Redlich, PRL 81(1998) 5284 Fodor, Katz JHEP04(2004)050 Freeze-out parameters approach Lattice-QCD phase boundary ~at SPS energies FO at E  1GeV per particle  Success of Statistical Models describing particle yields  Chemical freeze-out: T ch , μ B  SIS  RHIC At RHIC (and may be SPS) chemical freeze-out may probe the phase boundary: Insensitive to centrality

Xi’an 2006 STAR 12 Transverse mass spectra at mid-rapidity: Evidence for Thermalization? , K, p  T= 90MeV,   T=160MeV,  1/p T dN/dp T and E.Schnedermann, J. Sollfrank, U. Heinz PRC48 (1993) Blast-wave model , K, p  T = 90MeV,  = 0.6 c ,   T = 160MeV,  = 0.45 c

Xi’an 2006 STAR 13 Blast-Wave vs. Hydro Large flow, lots of re-interactions, thermalization likely T dec = 100 MeV Kolb and Rapp, PRC 67 (2003) Multi-strange spectra: Hydro: single T f.o What about fit quality? BW: lower T kin, higher  for ,K,p compared to  T kin ~ 90 MeV,  ~ 0.6 T kin ~ T ch ~ 160 MeV   ~ 0.45 rescattering at hadronization Is Blast-Wave realistic?

Xi’an 2006 STAR 14 Freeze-out Systematics T th [GeV] [c] T. Nayak SPS  RHIC: smooth systematic behavior of all global variables  Strong increase in radial flow ( ) from SIS to SPS  Changing trends of freeze-out parameters between AGS and SPS energies? Back to the Future  Low energy scan to find the “Landmark”

Xi’an 2006 STAR 15 What Points to Critical Point? ~ 1, ~2,  3 Gavai, Fodor, Ejiri, Gupta Katzet al  Large fluctuations are expected when hadronization is close to Critical Point Theory:  “Horn” structure in K + /  (smooth rise in K - /  )  Hadronic models do not reproduce the “horn”  Strong increase in K/  fluctuations towards lower energies Experiment:

Xi’an 2006 STAR 16  Particle Spectra and Yields – major tools to study soft sector  Success of Hydro and Statistical Models  At RHIC the final system appears to be in local equilibrium  Chemical FO at RHIC (SPS?) coincides with hadronization  Energy scan at RHIC could locate Landmark of Phase Diagram yields and ratios yields and ratios  T and  B High  B – Summary and Future Soft Hydro, Statistical Model

Xi’an 2006 STAR 17 High T – Probing Early Stage High-p T particle spectra  to address properties of the created medium and hadronization mechanisms in sQGP Hard pQCD, Fragmentation Jet quenching Energy loss mechanisms Energy Density Thermalization

Xi’an 2006 STAR 18 High-p T Hadron Suppression pQCD calculations of partonic energy loss Central Au+Au: x30 gluon density, x100 energy density  = GeV/fm 3 >>  C. Hadronic models: hadronic energy loss can explain at most 20% of the effect. ~p T -independence of measured R CP  unlikely that hadron absorption dominates jet quenching Look at the ratio of the hadron spectra: Large p T particles are suppressed in central Au+Au, but not in d+Au.

Xi’an 2006 STAR 19 nucl-ex/ Identified R AA /R CP  Particle-type dependence of R cp at the intermediate p T  Baryons exhibit less suppression  Or more enhancement?? hydro-like flow? gluon junction? coalescence/recombination? STAR: Nucl. Phys. A 757 (2005) 102 Two groups (2<pT<6GeV/c): , Ks, K , K*, φ  mesons p, Λ, Ξ, Ω  baryons

Xi’an 2006 STAR 20 Baryon Enhancement Intermediate p T :  Significant baryon/meson enhancement  Strong centrality dependence  Baryon/meson ratios become similar in AA and pp at p T ~ 6 GeV/c  Fragmentation is not dominant at p T < 6 GeV/c p+p  /K 0 s Au+Au 0-5%

Xi’an 2006 STAR 21 Color-charge effects on E-Loss Data: –No strong centrality dependence in ratios – Same suppression in R cp above 7 GeV/c not consistent with the jet quenching prediction ( X.N. Wang, PRC 58 (2321) 19) points to similar energy loss for partonic sources of p, pbar, and  STAR Preliminary Energy loss in QCD matter: –Possible to test expectations of higher energy loss for gluons vs. quarks X 2 or X 3 (S. Wicks et al., nucl-ex/ )

Xi’an 2006 STAR 22 Flavor-dependence of E-Loss Light vs. Heavy Flavor : u,d  c,b Similar energy loss for partonic sources of , p and non-photonic electrons

Xi’an 2006 STAR 23 Particle Yields and Spectra – major tools for experimental study of QCD matter:  Mapping the Phase Diagram  Observing Jet Quenching  Studying Thermalization  Energy Loss vs. Color-charge/Flavor Summary and Outlook Open Questions:  Establish that jet quenching is an indicator of parton E loss (Energy Scan would help to determine suppression turn-on, and study systematically quark vs. gluon jets)  Does the high initial gluon density inferred from parton E loss fits demand a deconfined initial state?  Location of the Critical Point (needs Energy Scan to higher  B )