Nuclear Modification Factors at Forward Rapidities in Au Au Collisions at RHIC

1
Nuclear Modification Factors at Forward
Rapiditiesin AuAu Collisions at RHIC

• J.H. Lee
• Physics Department
• Brookhaven National Laboratory
• For the BRAHMS Collaboration
• DNP04
• Oct. 29 2004

2
Rapidity Dependent High-pT Measurement
y0

• At the RHIC energies, hard scattering processes
  at high-pT become important
• Partons are expected to loose energy in the
  dense matter
• Different rapidities provide different densities
  of the medium Sensitive to the dynamics
• Largest medium effect at mid-rapidity (Scale
  to multiplicity)?
• Rapidity dependent high-pT suppression factors
  provide information on dynamical medium effect

at fixed time
high-y
Nucl-th/0108056 Polleri and Yuan
3
Nuclear Modification Factor Rcp Assumptions and
Definition

• Hard processes (incoherent) are
• expected to scale with the
• number of binary collisions Ncoll
• Peripheral collisions have minimum
• collective effect pp collisions

• sAuAu ? NbinsNN 1/4sNN
• dN/dh(h0)
• dN/dh(h2) 0.7dN/dh(h3.2)
• for central collisions

Three centrality bins using multiplicity in
hlt2 ltNcollgt for 0-10 880 ltNcollgt for
20-40 255 ltNcollgt for 50-90 21
4
Nuclear Modification Factor for Identified Hadrons
PHENIX PRC69 (2004)
AuAu 0-10/60-92 at y0

• Particle dependent nuclear modification factor
  observed
• at mid-rapidity
• Different suppression mechanism for Mesons and
  Baryons
• (Quark) Recombination models describe the data at
  y0
• At Forward Rapidity?

5

• Data and
  Analysis
• BRAHMS Full Forward Spectrometer Data at 4deg
  (h3.2)
• PID p, K, p using RICH
• Centrality using multiplicity in -2lthlt2
• Most pT-dependent systematics cancel out for Rcp
• Centrality dependent tracking efficicncy
  corrected

6
Rcp for h and h- at h3.2
BRAHMS Preliminary

• Rcp at h3.2 for charged hadrons
• Strong centrality dependence
• Rcp(0-10) lt Rcp(20-40)
• No significant h dependence
• in 0lthlt3.2
• Maximum at pT2GeV/c
• (rapidity independent soft-hard
• transition?)
• Rcp() gt Rcp(-)
• Systematic Errors
• - 10-15 overall
• - 10 p-by-p

h3.2
h2.2
h0
BRAHMS PRL 91 (2003)
7
3D-HydroJet
PRC 68 (2003) Hirano and Nara

• 3D Hydrodynamic Simulation with Jet (pQCD/PYTHIA)
• Qualitatively describe data with pseudo-rapidity
  dependence

8
Rcp for Identified Hadrons at y3
BRAHMS Preliminary
p
K

• Rcp for Identified particles at y3
• Suppression for all particles
• maximum at pT2GeV/c
• Rcp() Rcp(-) for p, K, p
• Rcp(p) gt Rcp(K) gt Rcp(p)

p,pbar

• Data

9
Rcp for Identified Negative Hadrons at y3 at
pT2 GeV/c

• Rcp for p-,K-,pbar
• Mass (or Baryon-Meson) dependent Rcp
• Stronger centrality dependence for pion
• Still significant quark recombination at y3
  ?

BRAHMS Preliminary
p-,K-,pbar
Duke model PRC 68, 044902 (2003)
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Summary and Outlook

• Suppression of high-pT hadron production
  relative to binary scaling
• at h3.2 in AuAu collisions at ?sNN 200 GeV
• No Strong rapidity dependence in suppression
  (0ltylt3)
• Strong Centrality dependent suppression
• Nuclear modification factor doesnt scale with
  multiplicity
• Significant quark recombination at y3?
• HydropQCD qualitatively describe nuclear
  modification
• factors in 0lthlt3.2
• Room for Initial state effect description?
• More forward data being analyzed (3deg. and 2.3
  deg. y3.5)
• Data analysis for RAuAu in progress
• More results on the way
• BRAHMS measures
• Energy/System/particle/rapidity/pT/reaction-plan
  e
• dependent Nuclear modification factor