Quark Matter 20051

Olga Barannikova (Olga Barannikova (Purdue University)Purdue University)

For the STAR CollaborationFor the STAR Collaboration

High-pT identified particle spectraHigh-pT identified particle spectra

Energy

System

200 GeV

62 GeV

Au+Au

d+Au

pp

p, p Motivation

Analysis technique

Preliminary results

Spectra, Ratios, Rcp

Summary

Quark Matter 20052

What’s known from data:What’s known from data:

baryon–meson difference in suppression factors nq-scaling of v2

p/p is independent of pT

PHENIX

p/ ratio increases with pT ~ 3-4 GeV/c

Quark Matter 20053

P, GeV/c

TPC CapabilityTPC Capability

3.0<pT<3.5 GeV/c

Particle/Antiparticle ratios can be extracted from h+/h-

p

N

Proton-pion separation > 2

3.0<pT<3.5 GeV/c+_

N

Quark Matter 20054

PID Techniques: rdE/dx FitsPID Techniques: rdE/dx Fits

PT, GeV/c

p

n

PT, GeV/c

wid

th

N

h+ –

h-

p

p

K

K yield is estimated from K0s

and TOF measurements-

Quark Matter 20055

……and bin counting:and bin counting:

p

K

STAR Preliminary

1-3% at 50% Eff , 10% at 70-90% Eff

Two Counting methods:

a) K + p= h - π (1) c1 p + c2 K=X (2)

b) c1 p + c2 K=X (2), where K is constrained by K0s

c1, c2 are K, p contributions, and X is the total yield in the counting region

Contamination:

Quark Matter 20056

Pion SpectraPion SpectraMinimum Bias: Centrality dependence:

Quark Matter 20057

Proton SpectraProton Spectra

Protons are inclusive here and thereafter

Centrality dependence:Minimum Bias:

Quark Matter 20058

--//+ + RatiosRatiosAu+Au min.bias

No pT or centrality dependence in -/ ratios

Au+Au central

d+Au min.bias

200 GeV

Quark Matter 20059

RatiosRatiosAu+Au min.bias

– no centrality dependence within errors

– decreases at high pT

Au+Au central

d+Au min.bias

I. Vitev and M. Gyulassy, Nucl. Phys. A 715 779 (2003).

— pQCD @ 130 GeV— Soft+Quench @ 130 GeV

pp /

200 GeV

Quark Matter 200510

Baryon ProductionBaryon Production200 GeV Au+Au, top 5%

– enhanced in intermediate pT range

– decreases at higher pT

Quark Matter 200511

Baryon production vs. CentralityBaryon production vs. Centrality

top 5% 40-80%

central

peripheral

– intermediate pT enhancement is higher in central events

Quark Matter 200512

Model PredictionsModel Predictions

— V. Greco, C.M. Ko, P. L`evai, Phys. Rev. C 68, 034904(2003), Phys. Rev. Lett. 90 202302 (2003).

— 200 GeV calculations based on I. Vitev and M. Gyulassy, Phys. Rev. C, 65, 041902(R) (2002).

— R. C. Hwa and C. B. Yang, Phys. Rev. C 70, 024905 (2004).

Variety of non-fragmentation contributions in the intermediate pT range:

Recombination/coalescence, Soft+Quench all show increase at low pT and a turnover to a falling distribution at pT~3GeV/c

Quark Matter 200513

Nuclear Modification FactorNuclear Modification Factor200 GeV Au+Au, Rcp 5 % / 40-80%

Recombination + Fragmentation:

R. J. Fries, S. A. Bass, et. al. nucl-th/0306027

–No difference between particles and antiparticles

Rcp

o -

• +

__

p

p

– Pronounced splitting in the intermediate pT range

– Rcp seems lower for pions and higher for protons with respect to NCh at higher pT :

alteration of fragmentation functions by the environment?

Quark Matter 200514

SummarySummary

Particle identification at high pT via relativistic rise in dE/dx; first results on pion and proton identification above 3 GeV/c

-/+ 1, no pT dependence for all data sets / centrality bins studied; p/p ratio decreases at high pT towards pQCD expected values

Enhancement in relative baryon to meson production at intermediate pT increases with centrality

Baryon/meson splitting in Rcp at intermediate pT