Global Observables PID Spectra From STAR Zhangbu Xu

Global Observables & PID Spectra From STAR Zhangbu Xu for the STAR Collaboration n Global Observables: n n Effect of Dense Medium on Particle Production and Resonance Properties n n Gluon Saturation Minijet Contribution Phase Transition Identified Particle Production & p. T Spectra Resonance Properties Future Programs Conclusions Zhangbu Xu, CIPANP 2003 1

EOS? n Multiplicity&<p. T> Initial related to Initial Condition or Phase Transition? n n n Hydrodynamics (collectivity) Thermalization/Equilibrium ? Final P. Kolb, et al Particle Production n n Identified Particle Flow Effect/Recombination Particle Properties in dense Medium L. Van Hove, PL 118 B (1982) 138 Zhangbu Xu, CIPANP 2003 2

Color. Glass. Condensate n n n Qs 2 ~ s(x. GA(x, Qs 2))/( RA 2) d. Nch/d /( RA 2) Qs 2/ s d. Nch/d /Npart 1/ s Gluon Saturation 1. Relevant Scale: Qs 2 d. Nch/d /( RA 2) J. Schaffner-Bielich, et al. nucl-th/0108048; D. Kharzeev, et al. hep-ph/0111315 2. Gluon Saturation Thermalization? A different view on the consequences of gluon saturation (A. Mueller, QM 02) Zhangbu Xu, CIPANP 2003 3

Effect of jet production on <p. T> Wang&Hwa PRD 39(1989)187 d. Nch/d = (1/2) Npart n s soft + n h. Nbin jet/ in minijet contribution Zhangbu Xu, CIPANP 2003 hard 4

How to Probe Dense Matter? n n Modification in medium Golden: J/ Decay quickly matter exists 10 -23 s q n Small or no FSI leptons, photons, neutrino s l q Small Branching Ratio(10 -4), Low Production Rate Zhangbu Xu, CIPANP 2003 l 5

Cleaner Way of Detecting Modification? Hadronic Decay at Late Stage n Lower Density n Lower Temperature n Smaller Effect n Hadronic Decay n Larger Signal n Extrapolation R. Rapp, et al. Last Call for RHIC Predictions Nucl. Phys. A 661 (1999) 205 -260 J. Schaffner-Bielich, et al. Zhangbu Xu, CIPANP 2003 6

All that Matters: Cross-section K* KK* measured * lost K K K* K K Chemical freeze-out Kinetic freeze-out K* measured K Different by 5 Rescattering>Regeneration at later stage Redistribution of momentum drives flow Zhangbu Xu, CIPANP 2003 7

STAR Detector Time Projection Chamber Magnet Coils Silicon Vertex Tracker TPC Endcap & MWPC FTPCs ZCal FPD Endcap FPD Vertex Position Detectors Calorimeter Barrel EM Calorimeter Central Trigger Barrel or TOF RICH Zhangbu Xu, CIPANP 2003 8

Multiplicity &Transverse Spectra Multiplicity reflects Geometry Centrality definitions: d. Nch/d , Impact Parameter, Participants ZDC cut d. Nh-/d | =0 = 280 1 20 d. Nch/d | =0 = 567 1 38 hminus: <p. T>=0. 508 Ge. V/c pp: 0. 390 Ge. V/c Zhangbu Xu, CIPANP 2003 9

p. T Centrality Dependence Hydro, P. Kolb RQMD N. Xu et al. QM 02 HIJING 200/130 ratio consistent with flat: both Nch and <p. T> Nch ratio: 1. 19 0. 05 (sys) <p. T> ratio: 1. 00 0. 02 (sys) Little centrality dependence we see no increase of <p. T> lose the early information? Maximum Missing Information thermalization? Dominant Soft Interaction Contribution? Zhangbu Xu, CIPANP 2003 10

Characteristics of Mean p. T n n 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: AA: ? ? ? soft+hard M. Szczekowski PRD 44 (1991) R 577 e+e-: along the thrust axis agrees with JETSET calculation ( OPAL PLB 320(1994)417) Zhangbu Xu, CIPANP 2003 11

Summary I n n n STAR Measures multiplicity and average transverse momentum of charged particles snn=200, 130 Ge. V <p. T> from AA has characteristic energy dependence NOT simple superposition of more elementary collisions Comparison with Models n n Saturation (no scaling between <p. T> and Qs) Two- component (not enough <p. T>) Transport Model (rescattering important) Possible due to early interaction and thermalization Zhangbu Xu, CIPANP 2003 12

Identified Particles n n Particle Yield p. T Spectra n n n Flow Hard Interactions In-medium Effect n Resonance Properties Zhangbu Xu, CIPANP 2003 13

Dominant Particles Spectra STAR Preliminary pp Measured from TPC d. E/dx Clear centrality dependence of spectra shape in pbar Zhangbu Xu, CIPANP 2003 14

Dominant Particles Centrality STAR Preliminary 1) , K, p mean transverse momentum <p. T> increase in more central collisions; 2) Heavier mass particle <p. T> 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 2003 15

<p. T> Mass Dependence p+p collisions (m. b. ) All fit to thermal (T, b. T) = (0. 17, 0) Except Au+Au collisions (5%) All fit to thermal (T, b. T) = (0. 1, 0. 6 c) Except W (T, b. T) = (0. 17, 0. 3 c) (1) W- + W+ (10%) Larger Flow Effects when • Larger Nucleus • Higher Beam Energies • Heavy Particles SPS RHIC Same Hadronic Phase, But higher W flow? Partonic collectivity? Zhangbu Xu, CIPANP 2003 16

Different Mass Particles At p. T ~ 2 -3 Ge. V/c, yields approach each other. Heavier mass particles show stronger collective flow effects ! Zhangbu Xu, CIPANP 2003 17

Similar Mass Particles n Spectra Different at Low p. T (p. T<1. 5 Ge. V/c) Similar at higher p. T n Reflect in <p. T> n 1. 2. 3. Slightly different in <p. T> due to low p. T Higher p. T contribution is significant W shows larger flow Flow, recombination? p, , X (5%); *, , W (10%) Zhangbu Xu, CIPANP 2003 18

What Determines p. T Spectra? STAR Preliminary /K Independent of anything non-interacting at hadronic stage? pp Au. Au: Power. Law Mt Exponential hard contribution thermal-like source? Zhangbu Xu, CIPANP 2003 19

Scattering Effects Thermal Production STAR Preliminary 1. 2. K*/K independent of Beam Energies (pp, e+e-) Low K* Production in Au. Au Zhangbu Xu, CIPANP 2003 20

Resonance Invariant Mass Distribution Au+Au 40% to 80% STAR Preliminary pp Minimum Bias STAR Preliminary 1. 2 p. T 1. 4 Ge. V/c 0. 8 p. T 0. 9 Ge. V/c |y| 0. 5 K*0 |y| 0. 5 *(1520) STAR preliminary p+p at 200 Ge. V ++ -- Zhangbu Xu, CIPANP 2003 , f 0(980), , *(892), *(1385), *(1520) , D* 21

Mass & Width of Resonances STAR Preliminary Phase Space Scattering Interference Modifications Zhangbu Xu, CIPANP 2003 22

Direct Measure of Open Charm D± Kππ D 0 Kπ STAR Preliminary |y|<1, p. T < 4 Ge. V/c • • Charm Production c c J/ Heavy Quark Energy Loss Flavor Tagging |y|<0. 25, 7< p. T <10 Ge. V/c 20 M d+Au Minbias Events Resonance Method: without secondary Vertex (statistical) Future upgrade: Micro-vertex detector (event-by-event) Zhangbu Xu, CIPANP 2003 23

MRPC TOF Barrel n n n Multi-gap Resistive Plate Chamber New Technology, Low Cost(glass+fishing line), High Resolution (<100 ps) One tray (1/120) prototype in d+Au run (2 month ago) Hadron PID (proton up to 3 Ge. V/c) (spectra, resonance, D) Electron PID (with TPC d. E/dx) upto 3 Ge. V/c Full Coverage for dileptons (including , , J/ ) Zhangbu Xu, CIPANP 2003 24

Conclusions n n Global Observables (Nch, <p. T>): different behavior from elementary collisions Large Flow n n n 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 2003 25

Soft and Hard Processes minijets CDF PRD 65 (2002) 072005 pp Et>1. 1 Ge. V 0 10 n n 20 30 40 charge multiplicity 0 10 20 30 40 charge multiplicity Momentum Scale: Qs , p 0 (~2 Ge. V) Soft: only depends on multiplicity (“sqrt”) Qs 2 Nch? Hard: energies, multiplicity (“linear”) Both have truth in them Zhangbu Xu, CIPANP 2003 26