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Pion, proton and anti-proton transverse momentum spectra in p+p and d+Au collisions at s NN = 200 GeV. Pawan Kumar Netrakanti,VECC, Kolkata ( for the STAR Collaboration ). Outline:. Motivation Method of analysis Results * Nuclear Modification Factor * Particle Ratios

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Outline:

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  1. Pion, proton and anti-proton transverse momentum spectra in p+p and d+Au collisions at sNN = 200 GeV Pawan Kumar Netrakanti,VECC, Kolkata (for the STAR Collaboration) Outline: • Motivation • Method of analysis • Results * Nuclear Modification Factor * Particle Ratios * Model Comparison * Scaling of particle production • Conclusions PANIC-2005, Santa Fe

  2. Motivation • High pT spectra in p+p collisions - test predictions from pQCD • pT spectra in p+p and d+Au collisions provides a reference spectra for nucleus-nucleus collisions. • Solid ground for models based on jet quenching and quark recombination • Study of Nuclear Modification Factor in d+Au collisions • Particle ratios constrain particle production models PANIC-2005, Santa Fe

  3. Log10(dE/dx) Log10(p) Momentum: GeV/c dE/dx of p (K,p) separation: 2s Detectors used : 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) Method of analysis Low pT :Particle identification by Time-Of-Flight ( pT < 2.5 GeV/c) High pT :Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. PANIC-2005, Santa Fe

  4. STAR preliminary Transverse Momentum Spectra Both functions give reasonable fits Power law function is pQCD inspired Levy ~ exponential + power law Power law : ( A/(1 + pT/p0)n) Levy : (B/(1+(mT-m0)/nT)n) PANIC-2005, Santa Fe

  5. STAR preliminary STAR preliminary Nuclear Modification Factor 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 PANIC-2005, Santa Fe

  6. 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 PANIC-2005, Santa Fe

  7. 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. PANIC-2005, Santa Fe

  8. STAR preliminary Model comparison – p+p collisions • NLO pQCD KKP and AKK fragmentation function and phenomenological EPOS Model are consistent with pion data at high pT (> 2 GeV/c) • pQCD with Kretzer FF under predicts pion data • NLO pQCD only with AKK FFs (Nucl.Phys.B725:181-206,2005) consistent with the p+pbar spectrum PANIC-2005, Santa Fe

  9. STAR preliminary Model comparison – d+Au collisions • NLO pQCD with KKP and AKK FFs and EPOS are consistent with pion data at high pT (> 4 GeV/c) • pQCD with Kretzer FF under predicts pion data • NLO pQCD with only AKK FFs consistent with the p+pbar spectrum Parton distribution functions : L. Frankfurt, et al., Phys. Rev. D 71 (2005) 054001 D. De Florian and R. Sassot, PRD 69 (2004) 074028 PANIC-2005, Santa Fe

  10. STAR preliminary STAR preliminary Scaling of particle production p,p(pbar) show xT (= 2pT/s) scaling for pT > 2 GeV/c at various CM energies mT scaling observed for 1 < mT < 2 GeV/c2 n ~ 4 for basic scattering process n ~ 8 quark meson scattering by exchanging a quark PANIC-2005, Santa Fe

  11. 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 PANIC-2005, Santa Fe

  12. 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 PANIC-2005, Santa Fe

  13. Highlight • 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 PANIC-2005, Santa Fe

  14. Backup Slides (Comparison with PHENIX) PANIC-2005, Santa Fe

  15. Backup Slides (e+e- scaling) Scaling in e+e- collisions PANIC-2005, Santa Fe

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