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N uclear M odification F actors at BRAHMS

N uclear M odification F actors at BRAHMS. Eun-Joo Kim ( Chonbuk Nat. Univ.) Hongyan Yang ( Univ. of Bergen ) For the Collaboration. BRAHMS experiment Nuclear Modification Factor - rapidity, system, energy dependence - dAu, AuAu, CuCu at 200, 62.4 GeV Summary. Outline.

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N uclear M odification F actors at BRAHMS

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  1. Nuclear ModificationFactors at BRAHMS Eun-Joo Kim ( Chonbuk Nat. Univ.) Hongyan Yang ( Univ. of Bergen ) For the Collaboration

  2. BRAHMS experiment Nuclear Modification Factor - rapidity, system, energy dependence - dAu, AuAu, CuCu at 200, 62.4 GeV Summary Outline

  3. It’s theBroad RAnge Hadron Magnetic Spectrometers! Au Au 90o d Au 30o 30o Cu Cu p p 15o 2.3o

  4. BRAHMS studies the properties of the produced medium as a function of rapidity… • At the RHIC energies, hard scattering processes at high-pT become important. • Partonsare expected to loose energy in the dense matter • Different rapidities provide different densities of the medium : study nuclear modification in AA, dA with respect to pp via Ncoll scaling to learn about QCD dynamics • “Dialing” initial condition channel • Rapidity dependent high pT suppression factors : provide information on dynamical medium effect pp collisions: we need this as reference dAu collisions AuAu & CuCu collisions

  5. yield in AA/number of equivalent pp collisions RAA = yield in pp yield in central events/<Ncoll>cent Rcp = yield in peripheral events/<Ncoll>peripheral Nuclear Modification Factor - quantify the nuclear effects

  6. enhancement suppression BRAHMS, PRL91, 072305(2003) RdAu, RAuAu at =0, ~2.2 RCP(h~2.2) RCP(h~0) ▪ R(h~0) ~ R(h~2) ▪ Absence of suppression in dAu at =0 ▪ Suppression in central AuAu is a final-state effect Nuclear Modification at higher rapidity ▪ Longitudinally extendedsource? ▪ And/or Initial state effect enhancing?

  7. increasing suppression Cronin like enhancement centrality dependence reversed at forward rapidities Increasing centrality BRAHMS PRL93(2004)242303 dAu results as a function of h & centrality The data are described by CGC models [PLB599(2004) 23], and have given rise to other interpretations and additional measurements. [Phys. Rev. C71 (2005) 024902]

  8. Rapidity dep. RAuAu : h± at 200 GeV High pT suppressions persists over 3 units in h 0-10%

  9. Centrality dependence of RAuAu & RCP no significant rapidity dependence no significant rapidity dependence more peripheral, less suppression ! ▪high pT suppression (pT> 2 GeV/c) observed at higher his similar to that ath~0

  10. RAuAu of hadron at 62.4 GeV BRAHMS Preliminary ▪ RAuAu(62.4GeV) > RAuAu(200 GeV) at pT > 2GeV/c & no rapidity dependence ▪ more peripheral, less suppression : depends on geometry of system? ▪ consistent with weak effects of a dense medium and a return of Cronin type enhancements

  11. RCP, RCuCu of hadron at 62.4 GeV ▪ no pT dependence ▪ no dependence on system size ▪ no rapidity dependence BRAHMS Preliminary

  12. Rh from RCP at 200, 62.4 GeV BRAHMS Preliminary Rh =RCP(h) / RCP(h~0) AuAu 200 GeV 62.4 GeV ▪ R(h~3) < R(h~0.9)at low energy

  13. RCP at CuCu 200 GeV ▪ more suppression as the collisions become more central ▪ little dependence on h ▪ similar effect as seen AuAu

  14. RCP : dependency on system size at 200 GeV (0-20%)/(60-80%) h = 3.2 centrality Npart ------------------------------------ CuCu 0-10% 96.8 40-60% 17.2 AuAu 33-43% 96.3 59-79% 15.7 dAu 0-20% 14.6 60-80% 4.8 pT [GeV/c] • Forward central CuCu looks like forward peripheral AuAu ▪ RCP depends on Npart

  15. RAuAu, RCP(p, p) at 200GeV Suppression for pions 0-10% y=0 y~1 y~3.1 BRAHMS Preliminary RAuAu: p < p

  16. RdAu at Forward rapidity more suppressed at forward BRAHMS Preliminary PHENIX PRC74, 024904(2006) baryons : enhancement RdAu(p) suppression up to 2.5 GeV/c

  17. ▪ Shadowing + MS + Energy Loss ▪ “Extracted“ opacity indicateslongitudinally traveling partons see less colored field ▪ Not a prediction : Assuming rapidity independent suppression factor Forward Tomography: Dynamics + Geometry G. Barnaföldi, Lévai, Papp, Fai: nucl-ph/0609023 L/l : mean value of jet scattering

  18. Nuclear Modification Factors at BRAHMS show ▪ suppression at forward rapidity, too : RAA, RdAu ▪ no significant rapidity dependence : RAA Non-hadronic energy loss through the medium in |y|<3: ▪ centrality dependence ( the geometry of the system ) : RAA, RdAu ▪ energy dependence, quantitatively : RAA ▪ more suppression for mesons than baryons : RAuAu, RdAu Summary • Forward suppression indicates that there most likely is some interplay • between initial state (e.g. shadowing) and final state (suppression in • the thin slice of deconfined matter, energy loss) effects. • needs more theoretical/experimental understanding on dynamics of particle suppression/production at RHIC

  19. The Collaboration I. Arsene9,11, I.G. Bearden6, D. Beavis1, S.Bekele10, C. Besliu9, B. Budick5, H. Bøggild6, C. Chasman1, C. H. Christensen6, P. Christiansen6, R.Clarke9, R.Debbe1, J. J. Gaardhøje6, K. Hagel7, H. Ito1, A. Jipa9, J. I. Jordre8, F. Jundt2, E.B.Johnson10, J.I.Jordre8, C.Jørgensen6, R. Karabowicz3, E. J. Kim10, T.M.Larsen6, J. H. Lee1, Y. K.Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3 , M. Murray10, J. Natowitz7, B.S.Nielsen6, D.Ouerdane6, R.Planeta3, F. Rami2, C.Ristea6, O.Ristea9, D. Röhrich8, B. H. Samset11, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7, H.Yang8, Z. Yin8,and I. S. Zgura9 1Brookhaven National Laboratory, USA 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Krakow, Poland 4Johns Hopkins University, Baltimore, USA 5New York University, USA 6Niels Bohr Institute, University of Copenhagen, Denmark 7Texas A&M University, College Station. USA, 8University of Bergen, Norway 9University of Bucharest, Romania 10University of Kansas, Lawrence,USA 11University of Oslo, Norway

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