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STAR identified particle measurements at high transverse momentum in p+p, d+Au and Au+Au collisions at s NN = 200 GeV. Pawan Kumar Netrakanti,VECC, Kolkata ( for the STAR Collaboration ). Outline:. Motivation STAR experiment Results  p+p collisions  d+Au collisions

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Outline:

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

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

  3. Brief overview of low pT results at RHIC Success of hydrodynamical models at low pT : pT spectra and Azimuthal Anisotropy Kinetic freeze-out conditions : From pT spectra peripheral central Chemical freeze-out conditions : From particle ratios Tch ~ 165 MeV RHIC/AGS User Meeting 2006, BNL

  4. Understanding high pT particle production at RHIC • Understanding the base line first : High pT 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 RHIC/AGS User Meeting 2006, BNL

  5. STAR experiment - Detectors Time projection Chamber (|h|<1.8, full f and 4.2 m long) Time-Of-Flight (–1.0 < h < 0 and p/30 in f) RHIC/AGS User Meeting 2006, BNL

  6. Log10(dE/dx) Momentum: GeV/c dE/dx of p (K,p) separation: 2s Log10(p) Particle Identification High pT :Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. Low pT :Particle identification by Time-Of-Flight ( pT < 2.5 GeV/c) RHIC/AGS User Meeting 2006, BNL

  7. Transverse Momentum Spectra pT spectra for pions, protons and anti-protons upto 10 GeV/c in pp and dAu collisions PLB 637 (2006) 161 STAR preliminary pT spectra for pions, protons and anti-protons upto 12 GeV/c in AuAu collisions RHIC/AGS User Meeting 2006, BNL

  8. Understanding the p+p collisions Sensitivity to choice of fragmentation function NLO pQCD calculations with Kretzer FF inconsistent with dataat midrapidity PLB637 (2006) 161 S. Kretzer, Phys. Rev. D 62 (2000) 054001 RHIC/AGS User Meeting 2006, BNL

  9. Sensitivity to choice of fragmentation function NLO pQCD calculations by W. Vogelsang PLB637 (2006) 161 NLO pQCD calculations with KKP FF are consistent with pion data at high pT (> 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p gp fragmentation is more in KKP RHIC/AGS User Meeting 2006, BNL

  10. Sensitivity to choice of fragmentation function PLB637 (2006) 161 NLO pQCD calculations with AKK FF are consistent with pion data at high pT (> 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 RHIC/AGS User Meeting 2006, BNL

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

  12. 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 pT (> 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 PLB637 (2006) 161 RHIC/AGS User Meeting 2006, BNL

  13. 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 xT (= 2pT/s) scaling for pT > 2 GeV/c at various CM energies PLB637 (2006) 161 RHIC/AGS User Meeting 2006, BNL

  14. At high pT : no scaling Mass effect Or baryon-meson effect mT scaling observed and absence of xT scaling for pT < 2 GeV/c  Dominance of hard process starts around pT ~ 2 GeV/c xT Scaling of particle production in p+p and d+Au mT scaling observed for 1 < mT < 2 GeV/c2 STAR preliminary More on mT scaling : Mark Heinz talk later today RHIC/AGS User Meeting 2006, BNL

  15. 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 YAsym = Yield Backward rapidity (Au-side) / Yield Forward rapidity (d-side) RHIC/AGS User Meeting 2006, BNL

  16. Comparison to Nuclear Shadowing Model Nuclear shadowing Model (Various parameterization of shadowing) R. Vogt Phys.Rev.C70:064902,2004 Cronin + Shadowing + Energy loss J. Qiu, I. Vitev PLB 632:507-511,2006 STAR preliminary STAR preliminary Incorporation of extremes of gluon shadowing (FGS) at low x does not reproduce the measured YAsym. Thereby providing an upper limit on contribution of nuclear shadowing to the YAsym. 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 RHIC/AGS User Meeting 2006, BNL

  17. Model comparison – EPOS model STAR preliminary PLB637 (2006) 161 Model does a reasonable job for Rapidity integrated spectra, but fails when we study forward and backward ratio EPOS model K. Werner, F. Liu, T. Pierog hep-ph/0506232 RHIC/AGS User Meeting 2006, BNL

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

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

  20. Particle ratio and double ratios can be used to get the relative fragmentation of u-quark to p- and p+ Fragmentation of u-quark to charged pions STAR preliminary It can be shown up- / up+ = 1 – rp/xp q-jet rp is the double ratio p-/p+ and xp 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p- / up+ ~ 0.3 – 0.6 RHIC/AGS User Meeting 2006, BNL

  21. d+Au : Nuclear Modification Factor Phys. Rev. Lett. 91 (2003) 072304 • At high pT,RdAu for p > 1, Cronin effect • Absence of high pT suppression in particle production STAR preliminary • RdAu (p + pbar) > RdAu (p) 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 STAR preliminary PLB637 (2006) 161 RHIC/AGS User Meeting 2006, BNL

  22. STAR Preliminary pT Au+Au : Nuclear Modification Factor Au+Au 200 GeV At high pT – particle production strongly suppressed. p+pbar and pion approach each other to a value of 0.3 RCP (p) > RCP (p) : 1.5 < pT < 7 GeV/c RCP (p+pbar) shows a decreasing trend at intermediate pT RHIC/AGS User Meeting 2006, BNL

  23. Particle Ratios – p+p collisions • p-/p+ ~ 1andpbar/p ~ 0.8 • p/p+ and pbar/p -increases with pT~ 2 GeV/c and then decreases to ~ 0.2 • p/p+ agrees with lower energy results. • pbar/p-shows a distinct energy dependence PYTHIA predicts a more prominent pTdependence for p-/p+andpbar/p and a flat dependence at high pT for p/p+ and pbar/p - PLB637 (2006) 161 RHIC/AGS User Meeting 2006, BNL

  24. Particle Ratios – d+Au collisions • p -/p+ ~ 1- independent of pT • pbar/p decreases with pT • p/p+ and pbar/p - increases with pT up to 2 GeV/c and then decreases. PLB637 (2006) 161 RHIC/AGS User Meeting 2006, BNL

  25. 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. RHIC/AGS User Meeting 2006, BNL

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

  27. Particle Ratios – Au+Au collisions STAR preliminary 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 pT~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>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). RHIC/AGS User Meeting 2006, BNL

  28. 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 xT scaling of p,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 RHIC/AGS User Meeting 2006, BNL

  29. Highlight – d+Au collisions • Significant Cronin effect observed for pion and proton in d+Au collisions with RdAu (p) > RdAu (p) at high pT • mT scaling together with xT scaling in p+p collisions shows that the dominance of hard over soft process for minbias collisions starts at pT ~ 2 GeV/c • Rapidity Asymmetry of identified particles can provide important information on relative contribution of various physical process to particle production RHIC/AGS User Meeting 2006, BNL

  30. Highlight – Au+Au collisions • In central Au+Au collisions, at high pT, RCP(p+pbar) ~ RCP() the p(pbar)/ ratios approach the ratios in p+p and d+Au collisions. This implies jet fragmentation mechanism region starts around pT>6 GeV/c • In Au+Au collisions, at pT>6 GeV/c: RCP(p+pbar) ~ RCP(); 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 RHIC/AGS User Meeting 2006, BNL

  31. 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 RHIC/AGS User Meeting 2006, BNL

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