Zhangbu Xu, CIPANP2003 1

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, CIPANP2003 2

EOS?

Initial ? Final

L. Van Hove, PL 118B (1982) 138

Multiplicity&<pT> 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, CIPANP2003 3

ColorGlassCondensate Qs

2 ~ s(xGA(x, Qs2))/(RA

2) dNch/d/(RA

2) Qs2/ s

dNch/d/Npart 1/ s

1. Relevant Scale: Qs2dNch/d/(RA

2)J. Schaffner-Bielich, et al. nucl-th/0108048; D. Kharzeev, et al. hep-ph/0111315

2. Gluon SaturationThermalization?A different view on the consequences of gluon saturation (A. Mueller, QM02)

Gluon Saturation

Zhangbu Xu, CIPANP2003 4

Effect of jet production on <pT>

Wang&Hwa PRD 39(1989)187

dNch/d = (1/2) Npartns

soft + nhNbinjet/in

hardminijet contribution

Zhangbu Xu, CIPANP2003 5

How to Probe Dense Matter?

Modification in medium

Decay quicklymatter exists 10-23s

Small or no FSIleptons, photons, neutrino

Golden: J/

q

q

l

l

s

Small Branching Ratio(10-4), Low Production Rate

Zhangbu Xu, CIPANP2003 6

Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260

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, CIPANP2003 7

All that Matters: Cross-section

Different by 5Rescattering>Regeneration at later stageRedistribution of momentum drives flow

Chemical freeze-out

Kinetic freeze-out

K*

lost

K*

measured

K

K* K

K*

K*

K

K*

K K K*

measured

Zhangbu Xu, CIPANP2003 8

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 FPD

Zhangbu Xu, CIPANP2003 9

Multiplicity reflects GeometryCentrality definitions:dNch/d, Impact Parameter, Participants

GeVsNN 130

Multiplicity &Transverse Spectra

dNh-/d|=0 = 280120dNch/d|=0 = 567 138

hminus:<pT>=0.508GeV/cpp: 0.390GeV/c

5.0||/

ddNh

ZDC cut

Zhangbu Xu, CIPANP2003 10

pT Centrality Dependence

200/130 ratio consistent with flat: both Nch and <pT>Nch ratio: 1.190.05 (sys)<pT> ratio: 1.00 0.02 (sys) Little centrality dependence

we see no increase of <pT> lose the early information?Maximum Missing Information thermalization?Dominant Soft Interaction Contribution?

Hydro, P. Kolb

HIJING

RQMDN. Xu et al. QM02

Zhangbu Xu, CIPANP2003 11

Characteristics of Mean pT

M. Szczekowski PRD 44 (1991) R577e+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+hardAA: ???

2ch

ppTpp

AAAAT

πR/dηdNs

a)p(ssap

Zhangbu Xu, CIPANP2003 12

Summary I STAR Measures multiplicity and average

transverse momentum of charged particlessnn=200, 130 GeV

<pT> from AA has characteristic energy dependenceNOT simple superposition of more elementary collisions

Comparison with Models Saturation (no scaling between <pT> and Qs) Two- component (not enough <pT>) Transport Model (rescattering important)

Possible due to early interaction and thermalization

Zhangbu Xu, CIPANP2003 13

Identified Particles

Particle Yield pT Spectra

Flow Hard Interactions

In-medium Effect Resonance Properties

Zhangbu Xu, CIPANP2003 14

Dominant Particles SpectraDominant Particles Spectra

Measured from TPC dE/dxClear centrality dependence of spectra shape in pbar

STAR Preliminary

pp

Zhangbu Xu, CIPANP2003 15

Dominant Particles CentralityDominant Particles Centrality

STAR Preliminary, K, p mean transverse momentum <pT> increase in more central collisions;

2) Heavier mass particle <pT> 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, CIPANP2003 16

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 TT= (0.17,0.3c)

- + + (10%)

<p<pTT> Mass Dependence> Mass Dependence

Partonic collectivity?Partonic collectivity?

Larger Flow Effects when• Larger Nucleus• Higher Beam Energies• Heavy ParticlesSPSRHIC Same Hadronic Phase, But higher flow?

Zhangbu Xu, CIPANP2003 17

Different Mass Particles

At pT ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects !

Zhangbu Xu, CIPANP2003 18

Similar Mass Particles

Spectra Different at Low pT (pT<1.5GeV/c)

Similar at higher pT

Reflect in <pT>1. Slightly different in <pT>

due to low pT2. Higher pT contribution is

significant3. shows larger flow

p,

Flow, recombination?

Zhangbu Xu, CIPANP2003 19

What Determines pT Spectra?

/K Independent of anything

non-interacting at hadronic stage?

STAR Preliminary

ppAuAu:

PowerLaw Mt Exponential

hard contribution thermal-like source?

Zhangbu Xu, CIPANP2003 20

Scattering Effects

Thermal Production

1. K*/K independent of Beam Energies (pp,e+e-)2. Low K* Production in AuAu

STAR Preliminary

Zhangbu Xu, CIPANP2003 21

Resonance Invariant Mass Distribution

STAR Preliminary

0.8 pT 0.9 GeV/c|y| 0.5

pp Minimum Bias Au+Au 40% to 80%

1.2 pT 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, CIPANP2003 22

Mass & Width of Resonances

Phase Space

Scattering

Interference

Modifications

STAR Preliminary

Zhangbu Xu, CIPANP2003 23

20M d+Au Minbias Events

Resonance Method:without secondary Vertex (statistical)

Future upgrade:

Micro-vertex detector (event-by-event)

D0Kπ D±Kππ

|y|<1, pT < 4 GeV/c|y|<0.25, 7< pT <10 GeV/c

Direct Measure of Open Charm

• Charm Production• ccJ/• Heavy Quark Energy Loss• Flavor Tagging

STAR Preliminary

Zhangbu Xu, CIPANP2003 24

MRPC TOF Barrel

Multi-gap Resistive Plate ChamberNew 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, CIPANP2003 25

Conclusions

Global Observables (Nch,<pT>): 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, CIPANP2003 26

Soft and Hard Processes

Momentum Scale: Qs , p0 (~2GeV)

Soft: only depends on multiplicity (“sqrt”) Qs2 Nch?

Hard: energies, multiplicity (“linear”) Both have truth in them

0 10 20 30 40 charge multiplicity

0 10 20 30 40 charge multiplicity

CDF PRD 65 (2002) 072005

Et>1.1GeV

pp

minijets