High pT Results from the BRAHMS Experiment

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High pT Results from the BRAHMS Experiment
Zhongbao Yin Department of Physics, University
of Bergen for the BRAHMS Collaboration
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The BRAHMS Experiment (II)
Run III
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Acceptance
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Why high pT physics is so interesting

• PQCD is applicable
• Probe and characterize the high energy density
  medium
• Disentangle different nuclear medium effects

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Experimental Measurements

• Invariant spectra of high pT particles
• Centrality dependence of high pT particle yields
• To compare with pp spectra, introduce the
  nuclear modification factor

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Event Selection

• Match up TPC and DC tracks in
• the magnets
• Point back to IP
• BB ZDC vertex

Centrality classes based on multiplicity
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Invariant Spectra of Charged Hadrons
Accepted for publication in PRL (nucl-ex/0307003)
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Nuclear Modification Factors
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Ratio of Rcp at h 2.2 and 0

• The degree of high pT suppression observed
  at h 2.2 is similar to or larger than at
  midrapidity
• How is this understood?

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Reminder
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dAu vs. Central AuAu Collisions

• High pT enhancement observed in dAu collisions
  at ?sNN200 GeV

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Particle Identification at Forward Rapidity

• H2 (TOF) for low momentum
• 2.5 sigma cuts
• K/p separation up to 3.8 GeV/c

• RICH for higher momentum
• 3 sigma cuts
• K/p separation up to 18 GeV/c

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Invariant Spectra for p- at y2.2
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Rcp at y2.2 for Negative Pion
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Another Reminder (QM'02)
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Summary

• AuAu at ?sNN 200 GeV
• ? Strong high pT suppression in central
  collisions observed both at midrapidity and at
  forward rapidity
• ? Suppression not observed in semi-peripheral
• collisions (40-60)
• A similar high pT suppression is seen for the
  identified negative pion spectra as found for the
  total negative charged hadron spectra
  (independent analysis)
• More work and more statistics needed in order to
  get the particle composition at high pT
• dAu at 200 GeV
• Enhancement of high pT yields observed at
  midrapidity. We will also investigate high pT
  yields at forward rapidity

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The BRAHMS Collaboration
I. Arsene10, I. G. Bearden7, D. Beavis1, C.
Besliu10, B. Budick6, H. Bøggild7, C. Chasman1,
C. H. Christensen7, P. Christiansen7, J. Cibor4,
R. Debbe1, E. Enger12, J. J. Gaardhøje7, M.
Germinario7, K. Grotowski4, K. Hagel8, O.
Hansen7, H. Ito1, 11, A. Jipa10, F. Jundt2, J. I.
Jørdre9, C. E. Jørgensen7, R. Karabowicz3, E. J.
Kim5, T. Kozik3, T. M. Larsen12, J. H. Lee1, Y.
K. Lee5, S. Lindal12, R. Lystad9, G. Løvhøiden2,
Z. Majka3, A. Makeev8, B. McBreen1, M.
Mikelsen12, M. Murray8, 11, J. Natowitz8, B.
Neumann11, B. S. Nielsen7, J. S. Norris11, D.
Ouerdane7, R. Planeta4, F. Rami2, C. Ristea10, O.
Ristea10, D. Röhrich9, B. H. Samset12, D.
Sandberg7, S. J. Sanders11, R. A. Scheetz1, P.
Staszel7, T. S. Tveter12, F. Videbæk1, R. Wada8,
Z. Yin9, I. S. Zgura10 1Brookhaven National
Laboratory, USA, 2IReS and Université Louis
Pasteur, Strasbourg, France 3Jagiellonian
University, Krakow, Poland, 4Institute of
Nuclear Physics, Cracow, Poland 5Johns Hopkins
University, Baltimore, USA, 6New York
University, USA 7Niels Bohr Institute, University
of Copenhagen, Denmark 8Texas AM University,
College Station, USA, 9University of Bergen,
Norway 10University of Bucharest, Romania,
11University of Kansas, Lawrence,USA 12
University of Oslo Norway