Zhangbu Xu, CIPANP Global Observables & PID Spectra From STAR Global Observables: Gluon Saturation Minijet Contribution Phase Transition Effect of Dense Medium on Particle Production and Resonance Properties Identified Particle Production & pT Spectra Resonance Properties Future Programs Conclusions Zhangbu Xu for the STAR Collaboration

Zhangbu Xu, CIPANP EOS? Initial ? Final L. Van Hove, PL 118B (1982) 138 Multiplicity& related to Initial Condition or Phase Transition? Hydrodynamics (collectivity) Thermalization/Equilibrium Particle Production Identified Particle Flow Effect/Recombination Particle Properties in dense Medium P. Kolb, et al

Zhangbu Xu, CIPANP ColorGlassCondensate Q s 2 ~  s (xG A (x, Q s 2 ))/(  R A 2 ) dN ch /d  /(  R A 2 )  Q s 2 /  s dN ch /d  /N part  1/  s 1.Relevant Scale: Q s 2  dN ch /d  /(  R A 2 ) J. Schaffner-Bielich, et al. nucl-th/ ; D. Kharzeev, et al. hep-ph/ Gluon Saturation  Thermalization? A different view on the consequences of gluon saturation (A. Mueller, QM02) Gluon Saturation

Zhangbu Xu, CIPANP Effect of jet production on Wang&Hwa PRD 39(1989)187 dN ch /d  = (1/2) N part  n  s soft +  n  h N bin  jet /  in hard minijet contribution

Zhangbu Xu, CIPANP How to Probe Dense Matter? Modification in medium Decay quickly matter exists s Small or no FSI leptons, photons, neutrino Golden:   J/  q qq l ll ss  Small Branching Ratio(10 -4 ), Low Production Rate

Zhangbu Xu, CIPANP Last Call for RHIC Predictions Nucl.Phys. A661 (1999) Cleaner Way of Detecting Modification? Hadronic Decay at Late Stage Lower Density Lower Temperature Smaller Effect Hadronic Decay Larger Signal Extrapolation R. Rapp, et al. J. Schaffner-Bielich, et al.

Zhangbu Xu, CIPANP All that Matters: Cross-section Different by 5 Rescattering>Regeneration at later stage Redistribution of momentum drives flow Chemical freeze-out Kinetic freeze-out K * lost K * measured   K K*K* K K*K* K*K*  K   K*K* K K

Zhangbu Xu, CIPANP STAR Detector ZCal Barrel EM Calorimeter Endcap Calorimeter Magnet Coils TPC Endcap & MWPC ZCal FTPCs Vertex Position Detectors Central Trigger Barrel or TOF Time Projection Chamber Silicon Vertex Tracker RICH FPD

Zhangbu Xu, CIPANP Multiplicity reflects Geometry Centrality definitions: dN ch /d , Impact Parameter, Participants Multiplicity &Transverse Spectra dN h -/d  |  =0 = 280  1  20 dN ch /d  |  =0 = 567  1  38 hminus: =0.508GeV/c pp: 0.390GeV/c ZDC cut

Zhangbu Xu, CIPANP  pT  Centrality Dependence 200/130 ratio consistent with flat: both Nch and Nch ratio: 1.19  0.05 (sys) ratio: 1.00  0.02 (sys) Little centrality dependence we see no increase of  lose the early information? Maximum Missing Information  thermalization? Dominant Soft Interaction Contribution? Hydro, P. Kolb HIJING RQMD N. Xu et al. QM02

Zhangbu Xu, CIPANP Characteristics of Mean pT M. Szczekowski PRD 44 (1991) R577 e+e-: along the thrust axis agrees with JETSET calculation ( OPAL PLB320(1994)417) AA: can not be treated as superposition of more elementary collisions pp: can not be treated as superposition of more elementary collisions e+e-: pure jets; pp: soft+hard AA: ???

Zhangbu Xu, CIPANP Summary I STAR Measures multiplicity and average transverse momentum of charged particles  s nn =200, 130 GeV from AA has characteristic energy dependence NOT simple superposition of more elementary collisions Comparison with Models Saturation (no scaling between and Qs) Two- component (not enough ) Transport Model (rescattering important) Possible due to early interaction and thermalization

Zhangbu Xu, CIPANP Identified Particles Particle Yield pT Spectra Flow Hard Interactions In-medium Effect Resonance Properties

Zhangbu Xu, CIPANP Dominant Particles Spectra Measured from TPC dE/dx Clear centrality dependence of spectra shape in pbar STAR Preliminary pp

Zhangbu Xu, CIPANP Dominant Particles Centrality STAR Preliminary , K, p mean transverse momentum increase in more central collisions; 2) Heavier mass particle increase faster than lighter ones as expected in hydro type collective flow. 3) Consistent with Nch within  1% 4)Particle ratios little centrality dependence 5)Scattering

Zhangbu Xu, CIPANP p+p collisions (m.b.)  All fit to thermal (T,  T ) = (0.17,0)  Except  Au+Au collisions (5%)  All fit to thermal (T,  T ) = (0.1,0.6c)  Except  T  T  = (0.17,0.3c)  - +  + (10%) Mass Dependence Mass Dependence Partonic collectivity? Larger Flow Effects when Larger Nucleus Higher Beam Energies Heavy Particles SPS  RHIC Same Hadronic Phase, But higher  flow?

Zhangbu Xu, CIPANP Different Mass Particles At p T ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects !

Zhangbu Xu, CIPANP Similar Mass Particles Spectra Different at Low pT (pT<1.5GeV/c) Similar at higher pT Reflect in 1. Slightly different in due to low pT 2. Higher pT contribution is significant   shows larger flow  p,  Flow, recombination?

Zhangbu Xu, CIPANP What Determines pT Spectra?  /K Independent of anything  non-interacting at hadronic stage? STAR Preliminary pp  AuAu: PowerLaw  Mt Exponential hard contribution  thermal-like source?

Zhangbu Xu, CIPANP Scattering Effects Thermal Production 1.K*/K independent of Beam Energies (pp,e+e-) 2.Low K* Production in AuAu STAR Preliminary

Zhangbu Xu, CIPANP Resonance Invariant Mass Distribution STAR Preliminary 0.8  p T  0.9 GeV/c |y|  0.5 pp Minimum Bias Au+Au 40% to 80% 1.2  p T  1.4 GeV/c |y|  0.5 STAR Preliminary K *0   *(1520) STAR preliminary p+p at 200 GeV , f0( 980 ), ,  *( 892 ),  *( 1385 ),  *( 1520 ) , D*  ++  -- 

Zhangbu Xu, CIPANP Mass & Width of Resonances Phase Space Scattering Interference Modifications STAR Preliminary

Zhangbu Xu, CIPANP M d+Au Minbias Events Resonance Method: without secondary Vertex (statistical) Future upgrade: Micro-vertex detector (event-by-event) D0KπD0Kπ D ±  K ππ |y|<1, p T < 4 GeV/c |y|<0.25, 7< p T <10 GeV/c Direct Measure of Open Charm Charm Production c  c  J/  Heavy Quark Energy Loss Flavor Tagging STAR Preliminary

Zhangbu Xu, CIPANP MRPC TOF Barrel Multi-gap Resistive Plate Chamber New Technology, Low Cost(glass+fishing line), High Resolution (<100ps) One tray (1/120) prototype in d+Au run (2 month ago) Hadron PID (proton up to 3GeV/c) (spectra, resonance,D) Electron PID (with TPC dE/dx) upto 3GeV/c Full Coverage for dileptons (including , , J/  )

Zhangbu Xu, CIPANP Conclusions Global Observables (Nch, ): different behavior from elementary collisions Large Flow Increase with beam energy, Nucleus Even particles with small hadronic  Spectra exhibit thermal production Possible Modification of Particle Properties Large Rescattering Effect on Resonance Spectra More rare, exciting probes to come

Zhangbu Xu, CIPANP Soft and Hard Processes Momentum Scale: Q s, p 0 (~2GeV) Soft: only depends on multiplicity (“sqrt”) Q s 2  Nch? Hard: energies, multiplicity (“linear”) Both have truth in them charge multiplicity charge multiplicity CDF PRD 65 (2002) Et>1.1GeV  pp minijets