Pion, proton and antiproton transverse momentum spectra in p p and d Au collisions at sNN 200 GeV

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Pion, proton and anti-proton transverse momentum
spectra in pp and dAu 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

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Motivation

• High pT spectra in pp collisions - test
  predictions from pQCD
• pT spectra in pp and dAu 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 dAu
  collisions
• Particle ratios constrain particle production
  models

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Method of analysis
Detectors used Time projection Chamber
(hlt1.8, full f and 4.2 m long) Time-Of-Flight
(1.0 lt h lt 0 and p/30 in f)
Low pT Particle identification by
Time-Of-Flight ( pT lt 2.5 GeV/c)
High pT Extend particle identification in TPC
by exploiting the relativistic rise in ionization
energy loss.
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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)
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Nuclear Modification Factor
Phys. Rev. Lett. 91 (2003) 072304

• RdAu for p gt 1, Cronin effect
• Absence of high pT suppression
• in particle production

• RdAu (p pbar) gt 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

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Particle Ratios pp collisions

• p-/p 1 and pbar/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

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Particle Ratios dAu 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.

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Model comparison pp collisions

• NLO pQCD KKP and AKK
• fragmentation function and
• phenomenological EPOS Model
• are consistent with pion data at
• high pT (gt 2 GeV/c)
• pQCD with Kretzer FF under
• predicts pion data

• NLO pQCD only with AKK FFs
• (Nucl.Phys.B725181-206,2005) consistent
• with the ppbar spectrum

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Model comparison dAu collisions

• NLO pQCD with
• KKP and AKK FFs and EPOS are consistent
  with pion data at high pT (gt 4 GeV/c)
• pQCD with Kretzer
• FF under predicts pion data

• NLO pQCD with only AKK FFs
• consistent with the ppbar
• spectrum

Parton distribution functions L. Frankfurt, et
al., Phys. Rev. D 71 (2005) 054001 D. De
Florian and R. Sassot, PRD 69 (2004) 074028
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Scaling of particle production
p,p(pbar) show xT ( 2pT/?s) scaling for pT gt 2
GeV/c at various CM energies
mT scaling observed for 1 lt mT lt 2 GeV/c2
n 4 for basic scattering process n 8 quark
meson scattering by exchanging a quark
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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
  dAu 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
  pp collisions.
• It seems to decrease with pT for dAu collisions

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Summary (Contd)

• Pion spectra for high pT is well explained
  using KKP AKK type of fragmentation function
  in pp and dAu collisions.
• NLO pQCD calculations with only AKK
  fragmentation functions explain the
  protonanti-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 pp and dAu
  collisions for mT lt 2 GeV/c2

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Highlight

• NLO pQCD describes the ppbar spectrum for the
  first time in pp collisions
• Importance of the significant improvement of FF
  for baryons from the light-flavor separated
  measurements in ee- 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

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Backup Slides (Comparison with PHENIX)
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Backup Slides (ee- scaling)
Scaling in ee- collisions