20-26 Feb. 2005 Lake Louise Eun-Joo Kim Parton energy loss, saturation, and recombination at BRAHMS Eun-Joo Kim University of Kansas For the BRAHMS collaboration

20-26 Feb. 2005 Lake LouiseEun-Joo Kim

Parton energy loss, saturation, Parton energy loss, saturation, and recombination at BRAHMSand recombination at BRAHMS

Eun-Joo KimEun-Joo KimUniversity of KansasUniversity of KansasFor the BRAHMS For the BRAHMS collaborationcollaboration


Hard scattering at RHIC Hard scattering at RHIC

study modifications modifications of high pT production in AA, dA with respect to pp via Ncoll scaling to learn about QCD dynamics : QQuark GGluon PPlasma and/or CColor GGlass C Condensate

RAA = (yieldAA/<Ncoll>)/yieldpp

Rcp = (yieldcentral/<Ncoll>cent)/(yieldperipheral/<Ncoll>peripheral)

coalescence

recombination


Parton dynamics in a dense system of gluons differs from pQCD parton saturation

CColor GGlass CCondensate (effective field theory of dense gluon systems) controls gluon density in hadron hadron collisions initial conditions for the QGPQGP ?

Evolution & Saturation Evolution & Saturation


BBroad RARAnge HHadron MMagnetic SSpectrometers


Experimental observationsExperimental observations

RdAu : enhancement

Au+Au

RAuAu & Rcp ~ suppression strong effect of dense medium dependence ? baryon-meson ~ different behavior BRAHMS

preliminary

BRAHMS PRL91(2003)072305

Au+Au

Rapidity dependence

Particle dependence


Rapidity dependant RRapidity dependant RdAudAu, R, Rcpcp

BRAHMS PRL93(2004)242303

Cronin like enhancement

increasing suppression

centrality dependence reversed at forward rapidities

consistent with CGC prediction: PLB599(2004) 23


But… Recombination also But… Recombination also works!works!

with only the recombination of soft and shower partonsno multiple scattering, or gluon saturation put in explicitly

Hwa & Yang : nucl-th/04010111

BRAHMS dAu data PRL93(2004) 242303

=2.2 =3.2

d+Au


RRAAAA for identified for identified hadronshadrons

=2.2

BRAHMS preliminary

- : strong suppression at ~0 & 2.2 in AuAu p : enhanced at ~2.2(AuAu), 3.2(dAu) collisions

Au+Au d+Au


peripheral collision pp collision

RRcp cp for identified hadrons in for identified hadrons in AuAuAuAu

BRAHMS preliminary

RRcpcp for for --, K, K--, p at y~3.2 at p, p at y~3.2 at pT T ~ 2GeV/c~ 2GeV/c

Mass (or Baryon-Meson) dependent Rcp

Stronger centrality dependence for “Still” significant quark recombination at

y~3.2 ?

Y~3.2


40-60%20-40%10-20%0-10% Energy dependence (SPSRHIC) pT = 3-4 GeV/c

pT=3-4GeV/c

RRAuAu AuAu at at ssNNNN = 62.4GeV = 62.4GeV

BRAHMS preliminary

~0.95

Suppression?


p/p/ Ratios in AuAu Ratios in AuAu

BRAHMS : PreliminaryPHENIX : PRC69(2004) 034909Hwa & Yang : PRC70(2004) 024905Greco & Ko, PRC68(2003) 034904

p/- ratios lower at forward rapidity while suppression persists? no significant difference between y=0 and y~1 flow/mass effect ?

Hwa & Yang : y=0 Greco & Ko : y=0


Ratios at Ratios at ~3.2 in dAu, ~3.2 in dAu, pppp

roughly as many protons as pions at high pT at forward rapidity in dAu

indicate other processes besides parton fragmentation

significant difference

small excess


summarysummary BRAHMS has measured rapidity dependent nuclear modification factors and particle ratios in AuAu, dAu, and pp collisions. In AuAu collisions at sNN=200GeV, - High pT suppression (mesons) observed at y ~ 0, 2.2, and 3.2. - No strong rapidity dependent suppression. - Suppression is smooth with energy at 63, 130, and 200GeV. In dAu collisions at sNN=200GeV, - significant reduction of the nuclear modification factor at

forward rapidity and this suppression increases with and the

centrality. Initial state can be described by parton saturation (CGC). Baryon vs. Meson : Production and Nuclear Modification - Recombination/Coalescence can give reasonable explanation at intermediate pT in AuAu and dAu collisions.


I.Arsene10, I. G. Bearden7, D. Beavis1, C. Besliu10, B. Budick6, H. Bøggild7, C. Chasman1,

C.H.Christensen7,P. Christiansen7, J. Cibor3, R. Debbe1, E. Enger12, J. J. Gaardhøje7, M. Germinario7, K. Hagel8, H. Ito1, A.Jipa10, F. Jundt2, J. I. Jørdre9, C. E. Jørgensen7,

R. Karabowicz4, E. J. Kim1,11, T. Kozik4 ,T. M. Larsen12, J. H. Lee1, Y. K. Lee5, S. Lindal12,

R. Lystad9, G. Løvhøiden12, Z. Majka4, A. Makeev8, M. Mikelsen12, M. Murray8, 11, J. Natowitz8,

B. Neumann11, B. S. Nielsen7, 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

1 Brookhaven National Laboratory, Upton, New York, USA2 IReS and Université Louis Pasteur, Strasbourg, France

3 Institute of Nuclear Physics, Krakow, Poland4 Smoluchkowski Inst. Of Physics, Jagiellonian University, Krakow, Poland

5 Johns Hopkins University, Baltimore, USA6 New York University, New York, USA

7 Niels Bohr Institute, University of Copenhagen, Denmark8 Texas A&M University, College Station, Texas, USA

9 University of Bergen, Bergen, Norway 10 University of Bucharest, Romania

11 University of Kansas, Lawrence, Kansas, USA 12 University of Oslo, Oslo, Norway

The BRAHMS CollaborationThe BRAHMS Collaboration

Documents

20-26 Feb. 2005 Lake Louise Eun-Joo Kim Parton energy loss, saturation, and recombination at BRAHMS Eun-Joo Kim University of Kansas For the BRAHMS collaboration