Recent Results from the BRAHMS Experiment at RHIC

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

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

The BRAHMS Collaboration 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. Mc. Breen 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 IRe. S 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 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 3

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

Charged Particle Multiplicity 0 -5% 5 -10% 10 -20% 20 -30% 30 -40% 0 -5% central Au+Au: Total charged particle multiplicity: 4630 370 (PRL 88, 202301(2002)) 50% increase over p+pbar (UA 5) 40 -50% p+p Energy density: Bjorken 1983 e. BJ = 3/2 (<Et>/ R 2 t 0) d. Nch/dh 4. 0 Ge. V/fm 3 (<Et>=0. 5 Ge. V, t 0=1 fm/c) P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 5

Limiting Fragmentation Shift the d. Nch/d distribution by the beam rapidity, and scale by Npart. Lines up with lower energy limiting fragmentation Au+Au s. NN=200 Ge. V (0 -5% and 30 -40%) Au+Au s. NN=130 Ge. V (0 -5%) Pb+Pb s. NN=17 Ge. V (9. 4%) P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 6

Baryon stopping y = yb - y y = 2. 03 0. 16 y = 2. 00 0. 1 Gaussians in pz 6 order polynomial Total E=25. 7 2. 1 Te. V 72 Ge. V per participant P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 7

Baryon stopping II y =0. 58 yp LHC l ica r i mp ? g lin a sc y = 2. 2, E /A=2800 Ge. V e broken Sscaling NN=63 Ge. V ? ? ? (Ebeam/A=3500 Ge. V, yp=8. 9) 8. 9 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 8

Kinetic freeze-out Chemical freeze-out Inc re ng i s a y PRL 90, 102301 (2003) BRAHMS preliminary • 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 Phys. Rev. Lett. 90, 102301(2003) T 115 Mev, T 0. 7 c 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 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 9

High pt Suppression Jet Quenching Ø Particles with high pt’s (above ~2 Ge. V/c) are primarly produced in hard scattering processes early in the collision Probe of the dense and hot stage Ø p+p experiments hard scattered Schematic view of jet production hadrons leading particle q partons fragment into jets of hadrons q Ø In A-A, partons traverse the medium v If QGP partons will lose a large part of their energy (induced gluon radiation) Suppression of jet production Jet Quenching leading particle Experimentally depletion of the high pt region in hadron spectra P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 10

Charged hadron invariant spectra BRAHMS, PRL 91(2003)072305 Nuclear Modification Factor RAA = h= 0 h= 2. 2 Yield(AA) NCOLL(AA) Yield(NN) Scaled N+N reference RAA<1 Suppression relative to scaled NN reference § Reference spectrum p+pbar spectra (UA 1) § SPS: data do not show suppression enhancent (RAA>1) due to initial state multiple scatering (“Cronin Effect”) P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 11

High pt suppression in Au+Au @ SNN=200 Ge. V BRAHMS, PRL 91(2003)072305 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 RCP= Yield(0 -10%)/NCOLL(0 -10%) Yield(40 -60%)/NCOLL(40 -60%) §RCP shows suppression at both =0 and =2. 2 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 12

Control measurement: d+Au @ SNN=200 Suppression in Au. Au 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 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 13

Hirano & Nara (nucl-th/0307087) Data versus Hydro-Jet Model i Hydro description of the soft part of the produced matter ii Hard part use a p. QDC model (PYTHIA) i+ii – generation of jets is evolving medium Reasonable description of data at both =0 and =2. 2 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 14

Evolution of Rd. Au with rapidity nucl-ex/0403005 Cronin like enhancement at =0 Clear suppression at =3. 2 Low pt consistent with measured d. Nch/d P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 15

p. QCD versus data @ = 3. 2 A. Accardi, M. Gyulassy, nucl-th/0402101 Geometrical shadowing with opacity from fit to PHENIX (y~0, 0) P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 16

Color Glass Condensate explanation =0 =1 D. Kharzeev at al. hep-ph/0405045 quark dipole-nucleus scattering amplitude Two free parameters fitted to data: y 0 – onset of saturation c - onset of quantum regime =2. 2 =3. 2 ØOveral good description of Rd. Au ØWith general trend of Rd. Au 1/Npart, this model accounts also for resonable description of RCP P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 17

Rapidity dependence for d+Au Submitted to PRL nucl-ex/0401025 Curves: Saturation Model from Kharzeev, Levin, Nardi NPA 730 (2004) 448 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 18

Summary v Large hadron multiplicies Almost a factor of 2 higher than at SPS ( higher ) Much higher than in pp ( medium effects) v Identified hadron spectra Broken lower energy scaling of rapidity loss Good description by statistical model large transvers flow v Suppression of high pt particles in central Au+Au collisions observed at =0 and 2. 2 Consistent with a Jet Quenching scenario v 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 P. Staszel - Jagellonian University, Kraków Eighth Workshop on Non-Perturbative QCD, Paris 2004 BRAHMS 19