1. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL1 STAR identified particle measurements at high transverse momentum in p+p, d+Au and Au+Au collisions at  s NN = 200 GeV Outline: Pawan Kumar Netrakanti,VECC, Kolkata ( for the STAR Collaboration ) Motivation STAR experiment Results  p+p collisions  d+Au collisions  Au+Au collisions Conclusions/Highlights

2. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL2 Low p T : Soft process, decides bulk properties of the matter and region where hydrodynamical models expected to work Intermediate p T : Recombination /Coalescence seems to lead to unique difference between baryon- meson production High p T : Hard process dominates, fragmentation is the mechanism of particle production, high pT suppression observed  Jet energy loss Understanding particle production at RHIC by studying p T spectra Motivation Focus of the talk

3. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL3 Brief overview of low p T results at RHIC Success of hydrodynamical models at low p T : p T spectra and Azimuthal Anisotropy Kinetic freeze- out conditions : From p T spectra Chemical freeze-out conditions : From particle ratios peripheral central T ch ~ 165 MeV

4. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL4 Understanding high p T particle production at RHIC  Understanding the base line first : High p T spectra in p+p collisions (  PDF + Cross section + FF)  Understanding the d+Au collisions : Bridges the gap between p+p and Au+Au collisions (Addition of Nuclear effects……) These shall provide solid grounds for models based on jet quenching and quark recombination  Understanding high pT particle production in Au+Au collisions by studying the Nuclear Modification Factor and particle ratios

5. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL5 STAR experiment - Detectors Time-Of-Flight (–1.0 <  < 0 and  /30 in  ) Time projection Chamber (|  |<1.8, full  and 4.2 m long)

6. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL6 Log10(p) Log10(dE/dx) Particle Identification High p T : Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. Low p T : Particle identification by Time-Of-Flight ( p T < 2.5 GeV/c) Momentum: GeV/c dE/dx of  K,p) separation: 2 

7. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL7 Transverse Momentum Spectra p T spectra for pions, protons and anti-protons upto 10 GeV/c in pp and dAu collisions p T spectra for pions, protons and anti-protons upto 12 GeV/c in AuAu collisions STAR preliminary PLB 637 (2006) 161

8. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL8 Understanding the p+p collisions Sensitivity to choice of fragmentation function NLO pQCD calculations with Kretzer FF inconsistent with data at midrapidity S. Kretzer, Phys. Rev. D 62 (2000) 054001 PLB 637 (2006) 161

9. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL9 Sensitivity to choice of fragmentation function NLO pQCD calculations by W. Vogelsang NLO pQCD calculations with KKP FF are consistent with pion data at high p T (> 2 GeV/c) They are inconsistent with the proton+anti-proton data KKP : B. A. Kniehl, G. Kraner and B. Potter, Nucl. Phys. B 597 (2001) 337 Difference between KKP and Kretzer FF is the way g   g   fragmentation is more in KKP PLB 637 (2006) 161

10. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL10 Sensitivity to choice of fragmentation function NLO pQCD calculations with AKK FF are consistent with pion data at high p T (> 2 GeV/c) NLO pQCD calculations with AKK FF compares relatively better than KKP for the p+pbar data AKK differ from KKP, in the way the light flavor FF are obtained from the light flavor separated measurements in e+e- collisions by OPAL AKK : S. Albino, B. A. Kniehl, and B. Potter, Nucl. Phys. B 725 (2005) 181 OPAL Collaboration : Eur. Phys. J. C 17 (2000) 207 PLB 637 (2006) 161

11. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL11 Gluon Jets Vs. Quark Jets Protons dominated by gluon FF & pions by quark FF at RHIC More Results : Mark Heinz talk later today Gluon jet contribution to protons is significantly larger than to pions at high p T in p+p collisions at RHIC.

12. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL12 Understanding the d+Au collisions pQCD calculations with Kretzer FF under predicts pion data NLO pQCD calculations with KKP and AKK FF and EPOS are consistent with pion data at high p T (> 4 GeV/c) NLO pQCD calculations with only AKK fragmentation function consistent with the p+pbar data Parton distribution functions : L. Frankfurt, et al., Phys. Rev. D 71 (2005) 054001 D. De Florian and R. Sassot, PRD 69 (2004) 074028 PLB 637 (2006) 161

13. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL13 Scaling of particle production in p+p collisions n ~ 4 for basic scattering process n ~ 5-8 depending on evolution of structure function and fragmentation function Pions,protons and anti-protons show the x T (= 2p T /  s) scaling for p T > 2 GeV/c at various CM energies PLB 637 (2006) 161

14. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL14 Scaling of particle production in p+p and d+Au More on m T scaling : Mark Heinz talk later today m T scaling observed and absence of x T scaling for p T < 2 GeV/c  Dominance of hard process starts around p T ~ 2 GeV/c xTxT At high p T : no scaling Mass effect Or baryon-meson effect m T scaling observed for 1 < m T < 2 GeV/c 2 STAR preliminary

15. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL15 d+Au collisions : Rapidity asymmetry To understand the relative contribution of various physics effects to particle production mechanism in d+Au collisions we study Forward and backward rapidity Asymmetry ratio for identified particles Y Asym = Yield Backward rapidity (Au-side) / Yield Forward rapidity (d-side)

16. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL16 Comparison to Nuclear Shadowing Model Nuclear shadowing Model (Various parameterization of shadowing) R. Vogt Phys.Rev.C70:064902,2004 Incorporation of extremes of gluon shadowing (FGS) at low x does not reproduce the measured Y Asym. Thereby providing an upper limit on contribution of nuclear shadowing to the Y Asym. STAR preliminary Cronin + Shadowing + Energy loss J. Qiu, I. Vitev PLB 632:507-511,2006 Trend for Cronin Only is opposite to data. The model does a reasonable job for lower rapidity. Energy loss in cold nuclear matter for Vitev I < Vitev II STAR preliminary

17. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL17 Model comparison – EPOS model EPOS model K. Werner, F. Liu, T. Pierog hep-ph/0506232 Model does a reasonable job for Rapidity integrated spectra, but fails when we study forward and backward ratio STAR preliminary PLB 637 (2006) 161

18. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL18 Model comparison – Recombination Recombination model R. C. Hwa, C.B. Yang, R.J. Fries Phys.Rev.C71:024902,2005 Model does a reasonable job. It will be interesting to get the results from the model for pions and protons separately. STAR preliminary

19. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL19 Particle - antiparticle ratios Vs. rapidity At high p T and rapidities away from mid rapidity the role of valence quarks become important. We study this through  - /  + and pbar/p for peripheral dAu and n-tag (pA) collisions. p(uud) may induce more  + (u dbar) production then  - (d ubar) Within systematic errors difficult to see the effect. So we take double ratio (cancels most systematic errors) Clear difference in  - /  + ratio seen in The forward and backward regions STAR preliminary

20. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL20 Fragmentation of u-quark to charged pions Particle ratio and double ratios can be used to get the relative fragmentation of u-quark to  - and  + It can be shown u   - / u   + = 1 – r  /x  q-jet r  is the double ratio  - /  + and x  q-jet is the fraction of pions originating from quark jets Contrasting this with the NLO pQCD calculations using AKK FF we find the fraction u   - / u   + ~ 0.3 – 0.6 STAR preliminary

21. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL21 d+Au : Nuclear Modification Factor STAR preliminary Phys. Rev. Lett. 91 (2003) 072304  R dAu (p + pbar) > R dAu (  ) Similar dependence has been observed at lower energies. Phys. Rev D 19 (1979) 764 Qualitative agreement with recombination model for dAu collisions. Phys.Rev.Lett.93 (2004) 082302  At high p T, R dAu for  > 1, Cronin effect  Absence of high p T suppression in particle production PLB 637 (2006) 161

22. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL22 Au+Au : Nuclear Modification Factor R CP (p  > R CP (  : 1.5 < pT < 7 GeV/c R CP (p+pbar  shows a decreasing trend at intermediate p T At high p T – particle production strongly suppressed. p+pbar and pion approach each other to a value of 0.3 STAR Preliminary pTpT Au+Au 200 GeV

23. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL23 Particle Ratios – p+p collisions   - /  + ~ 1 and pbar/p ~ 0.8  p/   and pbar/   increases with p T ~ 2 GeV/c and then decreases to ~ 0.2  p/   agrees with lower energy results.  pbar/   shows a distinct energy dependence PYTHIA predicts a more prominent p T dependence for  - /  + and pbar/p and a flat dependence at high p T for p/   and pbar/   PLB 637 (2006) 161

24. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL24 Particle Ratios – d+Au collisions      ~ 1- independent of p T  pbar/p decreases with p T  p/   and pbar/   increases with p T up to 2 GeV/c and then decreases. PLB 637 (2006) 161

25. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL25 Color charge dependence of energy loss X.N. Wang: PRC58(2321)1998. PID spectra, centrality dependence of pbar/p and pbar/  ratios, address the color charge dependence of energy loss  To further understand how the gluon jet/quark jet interact with the medium created in Au+Au. collisions.

26. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL26 Particle Ratios – Au+Au collisions 1.  - /  + are consistently with flat at unity at all p T, no significant centrality dependence. 2. pbar/p ratio: no significant centrality dependence p T, parton energy loss underpredicts the ratios (X.N. Wang, PRC 58 (2321) 1998). STAR preliminary

27. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL27 Particle Ratios – Au+Au collisions  The p(pbar)/  ratios in Au+Au collisions show strong centrality dependence.  In central Au+Au collisions, the p(pbar)/  ratios reach maximum value at p T ~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at p T >5 GeV/c.  In general, parton energy loss models underpredict p/  ratios. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000). STAR preliminary

28. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL28 Highlight – p+p collisions NLO pQCD describes the p+pbar spectrum for the first time in p+p collisions Importance of the significant improvement of FF for baryons from the light-flavor separated measurements in e+e- collisions (OPAL) The observed x T scaling of ,p(pbar) at high pT also show dominance of hard processes related to PDF and FF Provide solid reference for effects of jet quenching and recombination in Nucleus-Nucleus collisions

29. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL29 Highlight – d+Au collisions Significant Cronin effect observed for pion and proton in d+Au collisions with R dAu (  ) > R dAu (p) at high p T m T scaling together with x T scaling in p+p collisions shows that the dominance of hard over soft process for minbias collisions starts at p T ~ 2 GeV/c Rapidity Asymmetry of identified particles can provide important information on relative contribution of various physical process to particle production

30. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL30 Highlight – Au+Au collisions In Au+Au collisions, at p T >6 GeV/c: R CP (p+pbar) ~ R CP (  ); p(pbar)/  ~ p(pbar)/  (d+Au,p+p) pbar/p ~ pbar/p (d+Au). These indicate that partonic sources of p(pbar) and  have similar energy loss In central Au+Au collisions, at high p T, R CP (p+pbar) ~ R CP (  ) the p(pbar)/  ratios approach the ratios in p+p and d+Au collisions. This implies jet fragmentation mechanism region starts around p T >6 GeV/c

31. Pawan Kumar NetrakantiRHIC/AGS User Meeting 2006, BNL31 Collaborators STAR The STAR Collaboration U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, 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 Netherlands: NIKHEF/Utrecht Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino South Korea: Pusan National University Switzerland: University of Bern STAR