Recent Results from the BRAHMS Experiment at RHIC Paweł Staszel, Jagellonian University for the BRAHMS Collaboration Eighth Workshop on Non-Perturbative QCD Paris, 7 – 11 June, 2004

2 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS The Relativistic Heavy Ion Collider Au+Au d+Au p+p Top energy:  s NN =200GeV

3 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS I.G. Bearden 7, D. Beavis 1, C. Besliu 10, B. Budick 6, H. Bøggild 7, C. Chasman 1, C. H. Christensen 7, P. Christiansen 7, J.Cibor 4, R.Debbe 1, E. Enger 12, J. J. Gaardhøje 7, M. Germinario 7, K. Hagel 8, O. Hansen 7, A.K. Holme 12, H. Ito 11, A. Jipa 10, J. I. Jordre 10, F. Jundt 2, C.E.Jørgensen 7, R. Karabowicz 3, E. J. Kim 5, T. Kozik 3, T.M.Larsen 12, J. H. Lee 1, Y. K.Lee 5, G. Løvhøjden 2, Z. Majka 3, A. Makeev 8, B. McBreen 1, M. Mikkelsen 12, M. Murray 8, J. Natowitz 8, B.S.Nielsen 7, K. Olchanski 1, D. Ouerdane 7, R.Planeta 4, F. Rami 2, D. Röhrich 9, B. H. Samset 12, D. Sandberg 7, S. J. Sanders 11, R.A.Sheetz 1, P. Staszel 3,7, T.S. Tveter 12, F.Videbæk 1, R. Wada 8, Z. Yin 9, and I. S. Zgura 10 1 Brookhaven National Laboratory, USA, 2 IReS and Université Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland, 4 Institute of Nuclear Physics, Cracow, Poland 5 Johns Hopkins University, Baltimore, USA, 6 New York University, USA 7 Niels Bohr Institute, University of Copenhagen, Denmark 8 Texas A&M University, College Station. USA, 9 University of Bergen, Norway 10 University of Bucharest, Romania, 11 University of Kansas, Lawrence,USA 12 University of Oslo Norway 50 physicists from 12 institutions The BRAHMS Collaboration

4 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Agenda of this talk  General Characteristics of the Au+Au  s NN =200GeV - particle production - nuclear stopping - statistical model description (particle ratios) - transvers dynamics (particle p t spectra)  Nuclear modification of spectra Au+Au (QGP)  Rapidity evolution of nuclear modification for d+Au (CGC)  Summary

5 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Charged Particle Multiplicity 0-5% 5-10% 10-20% 20-30% 30-40% 40-50% Energy density: Bjorken 1983 e BJ = 3/2  ( /  R 2  0 ) dN ch /dh  4.0 GeV/fm 3 ( =0.5GeV,  0 =1fm/c) 0-5% central Au+Au: Total charged particle multiplicity: 4630  370 (PRL 88, (2002)) 50% increase over p+pbar (UA5) p+p

6 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Limiting Fragmentation Shift the dN ch /d  distribution by the beam rapidity, and scale by  N part . Lines up with lower energy  limiting fragmentation Au+Au  s NN =200GeV (0-5% and 30-40%) Au+Au  s NN =130GeV (0-5%) Pb+Pb  s NN =17GeV (9.4%)

7 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Baryon stopping 6 order polynomial Gaussians in pz  y  = yb -  y   y  = 2.03  0.16  y  = 2.00  0.1 Total  E=25.7  2.1TeV 72GeV per participant

8 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Baryon stopping II scaling broken empirical scaling  S NN =63 GeV ???  y  =0.58  y p 8.9 LHC  y  = 2.2,  E  /A=2800GeV (E beam /A=3500GeV, y p =8.9) ?

9 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS At y=0:  - /  + = 1.0, K - /K + = 0.95 ±0.05 pbar/p = 0.75 ±0.04 Good statistical model description with  B =  B (y), At |y|<1 mater  anti-matter Increasing y PRL90, (2003) Chemical freeze-out T  115 Mev,  T  0.7c at y=0 Flow velocity decreases with rapidity. Lower density  lower pressure  less flow Temperature increases with rapidity. Lower density  faster freeze out  higher temperature Kinetic freeze-out Phys. Rev. Lett. 90, (2003) BRAHMS preliminary

10 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS q q hadrons leading particle leading particle Schematic view of jet production  Particles with high p t ’s (above ~2GeV/c) are primarly produced in hard scattering processes early in the collision  Probe of the dense and hot stage Experimentally  depletion of the high p t region in hadron spectra  In A-A, partons traverse the medium  p+p experiments  hard scattered partons fragment into jets of hadrons  If QGP  partons will lose a large part of their energy (induced gluon radiation)  Suppression of jet production  Jet Quenching High p t Suppression  Jet Quenching

11 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Charged hadron invariant spectra h= 0 h= 2. 2 R AA = Yield(AA) N COLL (AA)  Yield(NN) Scaled N+N reference Nuclear Modification Factor R AA <1  Suppression relative to scaled NN reference  Reference spectrum p+pbar spectra (UA1)  SPS: data do not show suppression enhancent (R AA >1) due to initial state multiple scatering (“Cronin Effect”) BRAHMS, PRL91(2003)072305

12 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS High p t suppression in  S NN =200 GeV BRAHMS, PRL91(2003) mid-rapidity (  =0)  At central collisions clear suppression  At peripheral no suppression (as expected) forward rapidity (  =2.2)  the same trend no p+p reference  large sys. errors Yield(0-10%) / N COLL (0-10%) Yield(40-60%) / N COLL (40- 60%) R CP =  R CP shows suppression at both  =0 and  =2.2

13 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Control measurement:  S NN =200 Suppression in AuAu due to Jet Quenching or due to Initial State Parton Saturation (CGC)? What about d+Au? - Jet Quenching – No - CGC - Yes/No? Excludes alternative interpretation in terms of Initial State Effects  Supports the Jet Quenching for central Au+Au collisions + back-to-back azimuthal correlation by STAR

14 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Data versus Hydro-Jet Model i Hydro  description of the soft part of the produced matter ii Hard part  use a pQDC model (PYTHIA) i+ii – generation of jets is evolving medium Reasonable description of data at both  =0 and  =2.2 Hirano & Nara (nucl-th/ )

15 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Evolution of R dAu with rapidity Cronin like enhancement at  =0Clear suppression at  =3.2 Low pt consistent with measured dN ch /d  nucl-ex/

16 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS pQCD versus  = 3.2 Geometrical shadowing with opacity from fit to PHENIX (y~0,  0 ) A. Accardi, M. Gyulassy, nucl-th/

17 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Color Glass Condensate explanation D. Kharzeev at al. hep-ph/  =0  =1  =2.2  =3.2 quark dipole-nucleus scattering amplitude Two free parameters fitted to data: y 0 – onset of saturation c - onset of quantum regime  Overal good description of R dAu  With general trend of R dAu   1/N part, this model accounts also for resonable description of R CP

18 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Rapidity dependence for d+Au Submitted to PRL nucl-ex/ Kharzeev, Levin, Nardi NPA730 (2004) 448 Curves: Saturation Model from Kharzeev, Levin, Nardi NPA730 (2004) 448

19 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS Summary  Large hadron multiplicies  Almost a factor of 2 higher than at SPS (  higher  )  Much higher than in pp (  medium effects)  Evolution of nuclear modification in d+Au data  absence of the suppression in d+Au data at  =0 supports Jet Quenching scenario  forward data consistent with onset of suppression in the Color Glass Condensate  Suppression of high p t particles in central Au+Au collisions observed at  =0 and 2.2  Consistent with a Jet Quenching scenario  Identified hadron spectra  Broken lower energy scaling of rapidity loss  Good description by statistical model  large transvers flow