Properties of particle production at large transverse momentum in Au+Au and Cu+Cu collisions at RHIC

Outline

MotivationMeasurement (,p,pbar)Energy dependence ( √sNN = 62.4 and 200 GeV)System size dependence (Cu+Cu and Au+Au)Summary

Quark Matter 2006, Shanghai

Bedanga MohantyLawrence Berkeley National Laboratory

andVariable Energy Cyclotron Centre

(For STAR Collaboration)

Bedanga Mohanty Quark Matter 2006, Shanghai 2

Motivation (I)

Comparison to models constrains Initial gluon density (dNg/dY) Life time (Study vs. Energy, pT, Npart

Radiative or Collisional Eloss?

Jet quenching Nuclear Modification Factor

J. Alam et al, hep-ph/0604131

I Vitev : Radiative Eloss

ln RAA = -k Npart 2/3

hep-ph/0511237

Collisional Eloss

I. Vitev, PLB 606 (2005) 303X-N. Wang, PRC 70(2004) 031901

dNg/dY

Bedanga Mohanty Quark Matter 2006, Shanghai 3

Motivation (II)

Coalescence

Specific Energy dependence p/ (62.4 GeV) > p/ (200 GeV)

Time for quantitative comparison Data (Energy, pT, Npart) & Models (Baryon junction and Recombination ?)

p/ and pbar/

V. Greco, C.M. Ko and I. Vitev, PRC 71 (2005) 041901

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Motivation (III)

Color charge dependence of Eloss NMF and pbar/-

X-N. Wang, PRC 71(2005) 014903

xT = 2pT/√sNN

Eloss(g)/Eloss(q) ~ 9/4For same pT relativecontribution of quark and gluon jets differ at 62.4 and 200 GeV

Eloss(g)/Eloss(q) ~ 9/4One expects pbar/ in Au+Au < p+p at high pT

Observation : Similar (PRL 97 (2006) 152301)Need to understand gluon and quark jet interaction in medium - STAR Plenary Talk - Lijuan Ruan

W. Liu, C.M. Ko and B. W. Zhang, nucl-th/060704

STAR : PLB 637 (2006) 161

RA

A

pT

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Measurements

TPC

+ Au+Au 200 GeV

TOF

(-0.5 < || < 0.5)

(-1.0 < || < 0.0)

(STAR : PRL 97, 152301 (2006))

NIM A 499, 659 (2003)

NIM A 508, 181 (2003)

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Energy dependence : spectra & yields

√sNN = 62.4 GeV spectra steeper at high pT

Integrated yields

Proton yields : Interplay of baryon production and baryon transport at mid rapidity

peripheral central

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Energy dependence : Anti-particle-to-particle ratios

pbar/p at 62.4 falls off faster than 200 GeV. Baryon junction and coalescence models are close to data for intermediate pT

I Vitev et al.. NPA 715 (2003) 779c - baryon junction V. Greco et al., PRC 71 (2005) 041901 - coalescence

-/+ independent of pT

Model calculations with and without Eloss fail to explain pbar/p at high pT

Models : X-N. Wang et al PRC70(2004) 031901

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Energy and species dependence of NMF

Interplay of energy dependence of : initial jet spectra, dNg/dy and parton Eloss

Similar Eloss of partons

STAR : PRL 97, 152301 (2006)

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Energy dependence and Model comparison : NMF

Steeper initial jet spectra ?Or Color charge dependence ?At same pT : ~ 3 difference in xT

Suggests of radiative Eloss dominant

Plasma formation time < 3.6 fm/cV.S. Pantuev, hep-ph/0604268

pp 62 GeV : D. d’Enterria, J. Phys. G 31 (2005) S491

STAR Preliminary

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Energy dependence and Model comparison : NMF

dNg/dy (62.4) <800dNg/dy (200) > 800 ~> system sizeCollisional Eloss reasonable !

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Centrality and √sNN dependence : Baryon/meson

Strong centrality dependence

p/+(62.4) > p/+ (200)

p/-(62.4) < p/- (200)

Qualitative agreement with coalescence prediction

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Model comparison and scaling of Baryon/meson

Lack of quantitativeagreement with models

V. Greco et al PRC 72 (2005) 041901R.J. Fries et al PRC 68 (2003) 044902

I. Vitev et al PRC 65 (2002) 04902

The shape of the ratios at 2 energies around intermediate pT are similar

/K0s 200 GeV : nucl-ex/0601042

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Energy dependence in Cu+Cu system

Similar energy dependence inCu+Cu collisions as seen in Au+Aucollisions

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System size dependence

For collisions with similar Nbin and Npart the high pT results in Cu+Cu and Au+Au collisions are similar

- + +

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Summary

Intermediate pT

(2 - 6 GeV/c)

High pT

(>6 GeV/c)

Rcp () ~ RCP (p+pbar) : Similar Eloss of partons ? Indication of difference pT dependence of RAA () at 62.4 and 200 GeV : initial jet spectra or color charge effect ?p(pbar)/ ratios provide data to understand gluon and quark jet interactions in medium

p(pbar)/ : Qualitatively consistent with coalescence predictions but strong Quantitative disagreement Similar shape of p/pbar/ and/K0

s ratios at 62.4 and 200 GeV observed

Measurements +,-,p,pbar spectra measured in STAR upto pT = 12 GeV/c inAu+Au and Cu+Cu collisions at 62.4 and 200 GeV

System size For same Nbin, Cu+Cu and Au+Au results at high pT are similar

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STAR CollaborationU.S. Labs:

Argonne, Lawrence Berkeley, and Brookhaven National Labs

U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Illinois-Chicago, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale

Brazil: Universidade de Sao Paolo

China: IHEP - Beijing, IPP - Wuhan, USTC,Tsinghua, SINAP, IMP Lanzhou

Croatia: Zagreb University

Czech Republic: Nuclear Physics Institute

England: University of Birmingham

France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes

Germany: Max Planck Institute – Munich University of Frankfurt

India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC

Korea:Pusan Nat’l University

Netherlands:NIKHEF

Poland:Warsaw University of Technology

Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino

Thanks!

Bedanga Mohanty Quark Matter 2006, Shanghai 17

Back up slide (B/M ratio)

Bedanga Mohanty Quark Matter 2006, Shanghai 18

Back up slide (STAR-PHENIX)

p+p collisions

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Back up slide (NMF)

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Back up slide (NMF)

Strong centrality dependence

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Back up slide (B/M ratio)