Kein Folientitel

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p0 with high pT in pp, dAu and AuAu Collisions
Measured by the PHENIX Experiment
Henner Büsching Brookhaven National Laboratory
Hot-Quarks Workshop, Taos, July 23, 2004
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High pT Particle Production

• Mapping contributions of
• Initial-state effects
• Final-state effects

• Possible initial-state effects
• Initial-state multiple soft scatterings
  (Cronin effect)
  RAA gt 1
• Modifications of nuclear structure functions in
  nuclei (Shadowing) RAA
  lt 1
• Gluon-saturation (Color Glass
  Condensate) RAA lt 1 ?

• Final-state effects
• dense partonic medium parton energy loss (and
  recombination)
• (Jet Quenching)
• Dense hadronic medium hadronic energy loss

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PHENIX-Setup

• Relevant for this talk
• Detectors in the central spectrometer arms
• p0 via p0 ? gg
• Lead-scintillator calorimeter (PbSc)
• Lead-glass calorimeter (PbGl)
• Centrality, vertex
• Beam-Beam Counter (BBC) 3.0 lt h lt 3.9
• Zero-Degree Calorimeter (ZDC)

(pseudorapidity h lt 0.35)
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p0 production in pp

• Good agreement with NLO pQCD
• Factorization theorem

?AB ??hX ? fa/A(xa,Q2a) ??fb/B(xb,Q2b)
???a b ??cd ??Dh/c(zc,Q2c)
data vs pQCD
KKP Kretzer

• Constrains Fragmentation Function D(Gluon-pi)
• Reference for AuAu spectra

Phys. Rev. Let 91, 241803 (2003)
200 GeV - Run2
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p0 Spectra in AuAu at 200 GeV

• Use pp as base line measurement

• spectra up to 15 GeV/c

central
Nuclear Physics
Particle Physics
pT (GeV)
Phys. Rev. Lett. 91, 072301 (2003)
peripheral
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Nuclear Modification Factor RAA
integrated p0 yield above pT 4 GeV/c
Phys. Rev. Lett. 91, 072301 (2003)
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Jet Quenching?
Comparison with model calculations with and
without parton energy loss

• p0 suppression described by models
  with parton energy loss
• Additional nuclear effects needed to describe
  pT dependence
• Other explanations not ruled out at this stage

without parton energy loss
Levai
Wang
Wang
with parton energy loss
Vitev
Levai
dAu
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The Control Experiment dAu
Jet Quenching Models
RAB
1
dAu at ?sNN 200 GeV
Gluon Saturation
2-4 GeV/c
pT
Kharzeev, Levin, McLerran, hep-ph/0210332

• No suppression in dAu
• Initial-state effects ruled out as explanation
  for suppression in AuAu

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p0's in dAu Data vs. pQCD

• Data well reproduced by
• NLO pQCD calculation, plus
• Phenomenological model of Cronin-Effect, plus
• Shadowing

Levai et al., nucl-th/0306019
Kopeliovich et al., Phys. Rev. Lett. 88, 232303
(2002)
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p0 dAu centrality dependence
Phenix preliminary
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RdAu for different centralities
Phenix preliminary
Qualitative agreement with model by Accardi and
Gyulassy. Partonic
Glauber-Eikonal approach sequential multiple
partonic collisions. nucl-th/0308029 v2
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Centrality Dependence in dAu
Au Au Experiment
d Au Control Experiment
Preliminary Data
Preliminary Data
Final Data
charged
p0

• opposite behavior with increasing centrality in
  AuAu and dAu
• RAuAu decreases
• RdAu charged increases
• RdAu p0 increases

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Central to Peripheral
Phenix preliminary
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RAA for p0 in Central CollisionsDifferent
Energies
A.L.S.Angelis, PLB 185, 213 (1987) WA98, EPJ C
23, 225 (2002) Renormalization D.d'E.
nucl-ex/0403055 PHENIX, PRL 88 022301
(2002) PHENIX, PRL 91, 072303 (2003)
63 GeV AuAu
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?0 Spectra at 62 GeV
Phenix preliminary

• ?0 data in min. bias, 0-10 ,and 10-30 central
  collisions up to 7GeV/c
• Small systematic uncertainty 912

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62 GeV pp Reference for p0
/-25 uncertainty
p0 reference
(charged reference)
p0 reference
Talk by David dEnterria
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RAA for ?0 at 62GeV

• Ratios close to unity at pT2.5 GeV/c,
• then decreases
• Same tendency as 200 GeV Au-Au
• less suppression at intermediate pT.

p0 reference is used here
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RAA for ?0 at 62GeV suppression predictions
I. Vitev nucl-th/0404052
Adil Gyulassy nucl-th/0405036
RAA (p0) 0.5 - 0.3
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RAA for ?0 at 62 GeV
Vitev nucl-th/0404052
p0 reference is used here

• Reasonably good agreement (esp. high pT) within
  uncertainties
• Uncertainty in the pT shape (esp. low pT) of pp
  reference ...

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RAA for ?0 at 62GeV
Agreement with charged reference better Better
pp reference needed
charged reference h/p ratio is used here
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RAA for charged hadron

• p0 yield is multiplied by 1.6
• discrepancy between charged and p0
• Pions more suppressed than h/- at intermediate
  pT
• Large proton contribution up to at least 4GeV/c

charged
p0
0-10
charged
62.4 GeV
p0
charged reference is used here
10-30
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RAA for p0 in Central CollisionsDifferent
Energies
A.L.S.Angelis, PLB 185, 213 (1987) WA98, EPJ C
23, 225 (2002) Renormalization D.d'E.
nucl-ex/0403055 PHENIX, PRL 88 022301
(2002) PHENIX, PRL 91, 072303 (2003)
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Summary

• p0 at 200 GeV pp
• p0 at 62.4 and 200 GeV AuAu
• p0 at 200 GeV dAu
• Centrality dependence
• Inclusive spectra suppressed in AuAu
• by a factor of 4-5 at 200 GeV
• by a factor of 3 at 62.4 GeV
• No suppression in 200 GeV dAu
• Onset of suppression smooth with centrality
  and probably cm energy
• Stay tuned Always something new from PHENIX

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