BRAHMS High p T Results from the BRAHMS Experiment Zhongbao Yin Department of Physics, University of...

BRAHMSZhongbao Yin EPS2003

High pT Results from the BRAHMS

Experiment

Zhongbao YinDepartment of Physics, University of Bergen

for the BRAHMS Collaboration


The BRAHMS Experiment (II)

Run III


Acceptance

Rapidity

Tra

nsve

rse

mom

entu

m [

GeV

/c]


Why high pT physics is so interesting

● PQCD is applicable● Probe and characterize

the high energy density medium

● Disentangle different nuclear medium effects

hadrons

hadrons

leadingparticle

leadingparticle

qq


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:

R AA=d 2 N AA / d pT d y

N bin d 2 N NN / d pT d y


Event Selection

Centrality classes based on multiplicity

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


Invariant Spectra of Charged Hadrons

Accepted for publication in PRL (nucl-ex/0307003)


Nuclear Modification Factors


Ratio of Rcp

at= 2.2 and 0

● The degree of high p

T

suppression observed at= 2.2 is similar to or larger than at midrapidity● How is this understood?


Reminder


d+Au vs. Central Au+Au Collisions

• High pT enhancement

observed in d+Au collisions at sNN=200 GeV


Particle Identification at Forward Rapidity

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

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


Invariant Spectra for - at y=2.2


Rcp

at y=2.2 for Negative Pion


Another Reminder (QM'02)


Summary● Au+Au at sNN =200 GeV Strong high p

T 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 p

T

● d+Au at 200 GeV Enhancement of high p

T yields observed at midrapidity. We will also

investigate high pT yields at forward rapidity


The BRAHMS CollaborationI. 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, Poland5Johns Hopkins University, Baltimore, USA,

6New York University, USA7Niels Bohr Institute, University of Copenhagen, Denmark

8Texas A&M University, College Station, USA, 9University of Bergen, Norway

10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA

12 University of Oslo Norway

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