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Identified Hadron Spectra at Large Transverse Momentum in p+p and d+Au Collisions at 200 GeV

This seminar discusses the motivation, methods of analysis, and results of identified hadron spectra in p+p and d+Au collisions, focusing on high transverse momentum particles and understanding nuclear effects.

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Identified Hadron Spectra at Large Transverse Momentum in p+p and d+Au Collisions at 200 GeV

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  1. Identified hadron spectra at large transverse momentum in p+p and d+Au collisions at 200 GeV Bedanga Mohanty,VECC, Kolkata (Pawan Kumar Netrakanti and Zhangbu Xu for the STAR Collaboration) BNL Seminar, November 22nd 2005

  2. STAR preliminary STAR preliminary Outline • Motivation • Method of analysis • Results from p+p collisions • Results from d+Au collisions • Summary BNL Seminar, November 22nd 2005

  3. Motivation • High pT PID in TPC • Test predictions (certain aspects) of pQCD • Understanding Nuclear effects in d+Au collisions BNL Seminar, November 22nd 2005

  4. Method of analysis • Low pT – Time Of Flight (TOF) • High pT – Time Projection Chamber (TPC) Detectors : K. H. Ackerman et al., Nucl. Instrum. Methods Phys. Res., Sect. A 499 (2003) 624 TOF low pT results : STAR Collaboration, J. Adams et al., Phys. Lett. B 616 (2005) 8 Trigger & centrality : STAR Collaboration, J. Adams et al., Phys. Rev. Lett. 91 (2003) 072304 Phys. Rev. Lett. 92 (2004) 112301 rdE/dx method : M. Shao, et al., arXiv:nucl-ex/0505026 BNL Seminar, November 22nd 2005

  5. Hadron identification: STAR Collaboration, nucl-ex/0309012 Method of analysis : Detector - TOF PMD • A new technology ---- • Multigap Resistive Plate Chamber (MRPC) • adopted from CERN-Alice. • Intrinsic timing resolution: 85 ps in STAR • Coverage : -1.0 < h < 0.0 and p/30 in f • low pT particle identification ( < 2.5 GeV/c) in this study BNL Seminar, November 22nd 2005

  6. Log10(dE/dx) Log10(p) Momentum: GeV/c dE/dx of p (K,p) separation: 2s Method of analysis : Detector - TPC Time projection Chamber 45 padrows, radius 2 meters, |h|<1.8, full f and s(dE/dx) ~ 8% High pT :Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. Low pT BNL Seminar, November 22nd 2005

  7. Method of analysis • We obtain the ns(p) distribution for each pT bin • Then simultaneously fit them to 6 Gaussians • Constraints put by studying various parameters of dE/dx Proton yields : h ~ π + K + p (a) c1 p + c2 K=X (b) c1 p + c2 K=X where K is constrained by K0s c1, c2 are K, p contributions, and X is the total yield in the counting region BNL Seminar, November 22nd 2005

  8. How quarks are distributed in hadrons we collide Theory of particle production in p+p collisions How quarks and gluons fragment into hadrons What is the probability that 2 quarks will interact Quark Distribution Functions determined from deep-inelastic lepton-hadron collisions collide Hadron # 1 Quarks – fragment into hadrons Hadron # 2 Quark-Quark Cross-Section Determined from hadron-hadron collisions. Quark Fragmentation Functions determined from e+e- annihilations BNL Seminar, November 22nd 2005

  9. Provides a testing ground for next to leading order pQCD Why study particle production in p+p collisions at high pT PHENIX : PRL 91 (2003) 241803 P. Aurenche et al., EPJ C13, 347 (2000) What about p, protons and anti-protons ? • Proton spectra : • FF from e++e- works or not in p+p collisions ? • pQCD works best for scales pT >> mass BNL Seminar, November 22nd 2005

  10. Hadronization (by quark fragmentation ?) Why study particle production in p+p collisions at high pT If : p/p = q p / q p (p/p)AA ~ (p/p)pp p/p << 1 Nuclear effects (presence or absence ?) Crucial data for models : Jet quenching and Recombination BNL Seminar, November 22nd 2005

  11. Power law : ( A/(1 + pT/p0)n) Levy : (B/(1+(mT-m0)/nT)n) Transverse Momentum Spectra STAR preliminary • Power law function ~ pQCD inspired • Levy ~ exponential + power law Power law behaviour for p+p collisions at high pT BNL Seminar, November 22nd 2005

  12. STAR preliminary STAR preliminary p+p collisions and pQCD (Kretzer) NLO pQCD calculations with Kretzer FFinconsistent with dataat midrapidity S. Kretzer, Phys. Rev. D 62 (2000) 054001 BNL Seminar, November 22nd 2005

  13. STAR preliminary p+p collisions and pQCD (KKP) 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 STAR preliminary B. A. Kniehl, G. Kraner and B. Potter, Nucl. Phys. B 597 (2001) 337 NLO pQCD calculations by W. Vogelsang BNL Seminar, November 22nd 2005

  14. p+p collisions and pQCD (higher rapidity) • Inclusive forward p0 production in p+p collisions at 200 GeV consistent with NLO pQCD calculations • At small h, data consistent with KKP, as h increases data approaches cal. with Kretzer set of FF G. Rakness, nucl-ex/0501026 and D.A. Morozov, , hep-ex/0505024 BNL Seminar, November 22nd 2005

  15. p+p collisions and pQCD (AKK) NLO pQCD calculations with AKK FF are consistent with pion data at high pT (> 2 GeV/c) NLO pQCD calculations only with AKK FF (Nucl.Phys.B725:181-206,2005) consistent with the p+pbar data STAR preliminary AKK differ from KKP, in the way the light flavor FF are obtained OPAL Collaboration : Eur. Phys. J. C 17 (2000) 207 BNL Seminar, November 22nd 2005

  16. p+p collisions : Gluon or quark fragmentation NLO pQCD calculations with AKK FF shows significant contribution to pion production from gluon fragmentation at high pT STAR preliminary NLO pQCD calculations only with AKK FF shows gluon fragmentation dominant contributor to p+pbar yield at high pT BNL Seminar, November 22nd 2005

  17. Scaling in e++e- collisions e+ and e- does not have a parton distribution function There is no (sNN )nor (pT)n factor multiplied to cross section What happens in hadron-hadron collisions ? TPC Collaboration, H. Aihara, et al., Phys. Rev. Lett. 61 (1988) 1263 ARGUS Collaboration, H. Albrecht, et al., Z. Phys. C 44 (1989) 547 ALEPH Collaboration, D. Buskulic, et al., Z. Phys. C 66 (1995) 355 BNL Seminar, November 22nd 2005

  18. STAR preliminary Scaling in p+p collisions Spectra fitted to pTn (1-xT)m n ~ 4 for basic scattering process n ~ 8 quark-meson scattering by exchange a quark Pions,protons and anti-protons show the xT (= 2pT/s) scaling for pT > 2 GeV/c at various CM energies BNL Seminar, November 22nd 2005

  19. STAR preliminary p+p collisions and phenomenological model Phenomenological EPOS Model are consistent with pion data, even at low pT. Phenomenological EPOS Model are consistent with p + pbar data, even at low pT. Interesting to observe that two different models (pQCD and EPOS) do a reasonable job in pp collisions K. Werner, F. Liu and T. Pierog, hep-ph/0506232 BNL Seminar, November 22nd 2005

  20. Conclusions so far…. • For the first time it is observed that the proton + anti-proton spectra is consistent with NLO pQCD calculations using the AKK fragmentation functions. The AKK fragmentation functions are obtained from the light-flavor separated measurements on light charged hadrons in e+e- collisions by OPAL Collaboration • The pion, proton, and anti-proton production at high pT is consistent with pQCD calculations • This is independently verified by the observed xT scaling in pions, protons, and anti protons. BNL Seminar, November 22nd 2005

  21. Intrinsic kT , Cronin Effect Shadowing, EMC Effect Au + Au collisions p + p collisions d+Au collisions helps p+p  Au+Au collisions Parton Distribution Function Hard-scattering cross-section Fragmentation Function Parton Distribution Function Hard-scattering cross-section Partonic Energy Loss Fragmentation Function BNL Seminar, November 22nd 2005

  22. Phys. Rev. Lett. 91, No. 7, August 15, 2003 Phys. Rev. Lett. 91 (2003) What we know so far in d+Au collisions BNL Seminar, November 22nd 2005

  23. Cp ~ CK < Cp Does pQCD still work ? Do we understand RdAu (Cronin effect …recombination,shadowing, energy loss in cold nuclear matter ?) CGC models : Classical gluon production leads to Cronin effect. Nucleus pushes gluons To higher pT. At high energy and rapidity, the Cronin peak decreases. What more to study d+Au collisions at high pT J. W. Cronin, et al., Phys. Rev. D 11 (1975) 3105 D. Kharzeev, Y. Kovchegov and K. Tuchin, PLB 599 (2004) 23 BNL Seminar, November 22nd 2005

  24. What more to study d+Au collisions at high pT Cronin effect through recombination models Role of shadowing cannot be neglected Identified hadron data available (charged pions, protons and anti-protons) at high pT further our understanding R.C. Hwa and C. B. Yang, Phys. Rev. C 70 (2004) 037901 R. Vogt, Phys. Rev. C 70 (2004) 064902 BNL Seminar, November 22nd 2005

  25. STAR preliminary Power law : ( A/(1 + pT/p0)n) Levy : (B/(1+(mT-m0)/nT)n) Transverse Momentum Spectra • Power law function ~ pQCD inspired • Levy ~ exponential + power law Power law type behavior for d+Au collisions at high pT BNL Seminar, November 22nd 2005

  26. d+Au collisions and models • NLO pQCD calculations with KKP and AKK FF and phenomenological EPOS Model are consistent with pion data at high pT (> 4 GeV/c) • pQCD calculations with Kretzer FF under predicts pion data • 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 BNL Seminar, November 22nd 2005

  27. STAR preliminary Scaling of particle production mT scaling observed for 1 < mT < 2 GeV/c2 Another way of saying absence of flow effects At high pT : no scaling Mass effect Or baryon-meson effect BNL Seminar, November 22nd 2005

  28. STAR preliminary STAR preliminary Nuclear Modification Factor : d+Au collisions Phys. Rev. Lett. 91 (2003) 072304 • RdAu for p > 1, Cronin effect • Absence of high pT suppression in particle production • 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 BNL Seminar, November 22nd 2005

  29. RdAu : Centrality dependence RdAu increases with centrality BNL Seminar, November 22nd 2005

  30. Conclusion so far • Pion spectra for high pT is well explained using KKP & AKK type of fragmentation function in d+Au collisions. • NLO pQCD calculations with only AKK fragmentation functions explain the proton+anti-proton spectra • Significant Cronin effect in pion production in d+Au collisions. • The nuclear modification factor for baryons is higher than mesons in intermediate region of pT BNL Seminar, November 22nd 2005

  31. Particle Ratios – in p+p and p+A collisions Same-charge particle ratios for high pT hadrons p/p+ Vs. pT reflects FF ratio Dpu /Dp+ u A rapid drop of p/p+ with pT followed by a high pT flattening – scattered point-like diquarks as a source of high pT protons (Phys.Lett.B149:509,1984) A rapid drop of p/p+ with pT is reflective of Q2 dependence of diquark form factor pbar/p- : pbar must be produced by scattering of sea-quarks or gluons or rank ordering Decrease in pbar/p-  decreasing importance of these processes Opposite-charge particle ratios for high pT hadrons p-/p+ Vs. pT or x may reflect the d/u structure function ratio in protons pbar/p Vs. pT : p has valence quarks common with nucleons, so it may reflect the on fraction of protons of gluonic origin (assuming that gluons fragment equally into p and pbar). BNL Seminar, November 22nd 2005

  32. Particle Ratios – p+p collisions Phys. Rev D 19 (1979) 764 • p-/p+ decreases with pT in p+p collisionsfrom ~1.0 to 0.5 • p-/p+ independent ofpT in p+n collisions BNL Seminar, November 22nd 2005

  33. Particle Ratios – p+A collisions • p-/p+ decreases with pT from ~0.9 to ~ 0.6 • pbar/p decreases with pT from ~ 0.1 to 0.03 • p/p+ and pbar/p- decreases for pT > 4 GeV/c from ~ 0.6 to 0.06 Phys. Rev D 45 (1992) 3030 BNL Seminar, November 22nd 2005

  34. STAR preliminary Particle Ratios – p+p collisions • p-/p+ ~ 1andpbar/p ~ 0.8 • JETSET predicts a more prominent pT dependence Phys.Rev.C 58 (1998) 2321 • 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 BNL Seminar, November 22nd 2005

  35. STAR preliminary 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. BNL Seminar, November 22nd 2005

  36. Summary • Obtained the pT spectra for charged pions, protons and anti-protons up to 10 GeV/c. • Method used in high pT : relativistic rise in ionization energy loss in TPC • pT spectra is fitted to both Power law and Levy distributions • Significant Cronin effect in pion production in d+Au collisions. • The nuclear modification factor for baryons is higher than mesons in intermediate region of pT • The anti-proton/proton ratio is around 0.8 for p+p collisions. It seems to decrease with pT for d+Au collisions BNL Seminar, November 22nd 2005

  37. Summary (Contd…) • Pion spectra for high pT is well explained using KKP & AKK type of fragmentation function in p+p and d+Au collisions. • NLO pQCD calculations with only AKK fragmentation functions explain the proton+anti-proton spectra • A phenomenological model based on parton splitting (EPOS) also does a reasonable job • Pions and protons exhibit xT scaling. • mT scaling of pions and protons in p+p and d+Au collisions for mT < 2 GeV/c2 Thanks BNL Seminar, November 22nd 2005

  38. Conclusion so far BNL Seminar, November 22nd 2005

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