1. Properties of particle production at large transverse momentum in Au+Au and Cu+Cu collisions at RHIC Outline Motivation Measurement ( ,p,pbar) Energy dependence ( √s NN = 62.4 and 200 GeV) System size dependence (Cu+Cu and Au+Au) Summary Quark Matter 2006, Shanghai Bedanga Mohanty Lawrence Berkeley National Laboratory and Variable Energy Cyclotron Centre (For STAR Collaboration)

2. Bedanga MohantyQuark Matter 2006, Shanghai 2 Motivation (I) Comparison to models constrains Initial gluon density (dN g /dY) Life time (  Study vs. Energy, p T, N part Radiative or Collisional E loss ? Jet quenchingNuclear Modification Factor J. Alam et al, hep-ph/0604131 I Vitev : Radiative E loss ln R AA = -k N part 2/3 hep-ph/0511237 Collisional E loss I. Vitev, PLB 606 (2005) 303 X-N. Wang, PRC 70(2004) 031901 dN g /dY 

3. Bedanga MohantyQuark Matter 2006, Shanghai 3 Motivation (II) Coalescence Specific Energy dependence p/   (62.4 GeV) > p/   (200 GeV) Time for quantitative comparison Data (Energy, p T, N part ) & Models (Baryon junction and Recombination ?) p/   and pbar/   V. Greco, C.M. Ko and I. Vitev, PRC 71 (2005) 041901

4. Bedanga MohantyQuark Matter 2006, Shanghai 4 Motivation (III) Color charge dependence of E loss NMF and pbar/  - X-N. Wang, PRC 71(2005) 014903 x T = 2p T /√s NN E loss (g)/E loss (q) ~ 9/4 For same p T relative contribution of quark and gluon jets differ at 62.4 and 200 GeV E loss (g)/E loss (q) ~ 9/4 One expects pbar/  in Au+Au < p+p at high p T 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 R AA pTpT

5. Bedanga MohantyQuark Matter 2006, Shanghai 5 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)

6. Bedanga MohantyQuark Matter 2006, Shanghai 6 Energy dependence : spectra & yields √s NN = 62.4 GeV spectra steeper at high p T Integrated yields Proton yields : Interplay of baryon production and baryon transport at mid rapidity peripheral central

7. Bedanga MohantyQuark Matter 2006, Shanghai 7 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 p T I Vitev et al.. NPA 715 (2003) 779c - baryon junction V. Greco et al., PRC 71 (2005) 041901 - coalescence  - /  + independent of p T Model calculations with and without E loss fail to explain pbar/p at high p T Models : X-N. Wang et al PRC70(2004) 031901

8. Bedanga MohantyQuark Matter 2006, Shanghai 8 Energy and species dependence of NMF Interplay of energy dependence of : initial jet spectra, dN g /dy and parton E loss Similar E loss of partons STAR : PRL 97, 152301 (2006)

9. Bedanga MohantyQuark Matter 2006, Shanghai 9 Energy dependence and Model comparison : NMF Steeper initial jet spectra ? Or Color charge dependence ? At same p T : ~ 3 difference in x T Suggests of radiative E loss dominant Plasma formation time < 3.6 fm/c V.S. Pantuev, hep-ph/0604268 pp 62 GeV : D. d’Enterria, J. Phys. G 31 (2005) S491 STAR Preliminary

10. Bedanga MohantyQuark Matter 2006, Shanghai 10 Energy dependence and Model comparison : NMF dN g /dy (62.4) <800 dN g /dy (200) > 800  ~> system size Collisional E loss reasonable !

11. Bedanga MohantyQuark Matter 2006, Shanghai 11 Centrality and √s NN dependence : Baryon/meson Strong centrality dependence p/  + (62.4) > p/  + (200) p/  - (62.4) < p/  - (200) Qualitative agreement with coalescence prediction

12. Bedanga MohantyQuark Matter 2006, Shanghai 12 Model comparison and scaling of Baryon/meson Lack of quantitative agreement with models V. Greco et al PRC 72 (2005) 041901 R.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 p T are similar  /K 0 s 200 GeV : nucl-ex/0601042

13. Bedanga MohantyQuark Matter 2006, Shanghai 13 Energy dependence in Cu+Cu system Similar energy dependence in Cu+Cu collisions as seen in Au+Au collisions

14. Bedanga MohantyQuark Matter 2006, Shanghai 14 System size dependence For collisions with similar N bin and N part the high p T results in Cu+Cu and Au+Au collisions are similar  - +  +

15. Bedanga MohantyQuark Matter 2006, Shanghai 15 Summary Intermediate p T (2 - 6 GeV/c) High p T (>6 GeV/c) Rcp (  ) ~ R CP (p+pbar) : Similar E loss of partons ? Indication of difference p T dependence of R AA (  ) 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  /K 0 s ratios at 62.4 and 200 GeV observed Measurements  +,  -,p,pbar spectra measured in STAR upto p T = 12 GeV/c in Au+Au and Cu+Cu collisions at 62.4 and 200 GeV System size For same N bin, Cu+Cu and Au+Au results at high p T are similar

16. Bedanga MohantyQuark Matter 2006, Shanghai 16 STAR Collaboration U.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!

17. Bedanga MohantyQuark Matter 2006, Shanghai 17 Back up slide (B/M ratio)

18. Bedanga MohantyQuark Matter 2006, Shanghai 18 Back up slide (STAR-PHENIX) p+p collisions

19. Bedanga MohantyQuark Matter 2006, Shanghai 19 Back up slide (NMF)

20. Bedanga MohantyQuark Matter 2006, Shanghai 20 Back up slide (NMF) Strong centrality dependence

21. Bedanga MohantyQuark Matter 2006, Shanghai 21 Back up slide (B/M ratio)