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HIGH P T SUPRESSION AT FORWARD RAPIDITIES IN CU+CU AT =200 GeV

1. HIGH P T SUPRESSION AT FORWARD RAPIDITIES IN CU+CU AT =200 GeV Selemon Bekele for the BRAHMS Collaboration The University of Kansas PANIC 05 Santa Fe, New Mexico Oct. 24-28, 2005. 2. Outline. Introduction high p t suppression The BRAHMS experiment

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HIGH P T SUPRESSION AT FORWARD RAPIDITIES IN CU+CU AT =200 GeV

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  1. 1 HIGH PT SUPRESSION AT FORWARD RAPIDITIES IN CU+CU AT =200 GeV Selemon Bekele for the BRAHMS Collaboration The University of Kansas PANIC 05 Santa Fe, New Mexico Oct. 24-28, 2005

  2. 2 Outline • Introduction high pt suppression • The BRAHMS experiment pt spectra particle ratios Rcp in CuCu and AuAu • Summary

  3. 3 Introduction High pt suppression at η = 0 Brahms PRL 91(2003) Suppression of high pt hadron production has been observed in AuAu collisions at mid rapidity In contrast no suppression has been seen in dAu collisions This observation led to the hypothesis that high pt suppression may be a final state effect Possible explanations: jet quenching, parton recombination How about forward rapidities ?

  4. 4 Brahms PRL 91(2003) 1 2 3 4 5 1 2 3 4 5 pt [GeV/c] pt [GeV/c] High pt suppression has been observed away from mid rapidity AuAu.

  5. 5 High Pt suppression: RdAu versus η Clear suppression as  changes from 0 to 3.2 Measurements very consistent with initial-state effects estimated by CGC: gluon saturation, gluon shadowing Brahms PRL 93 (2004) D. Kharzeev hep-ph/030737

  6. 6 High Pt suppression: Rcp versus η Assuming peripheral collisions are like pp, one can look at Rcp defined below [H. Weber, UrQMD] Rcp is suppressed in AuAu collisions at forward rapidities leaving room for initial state effects as possible explanations η~3.2 Brahms PRL 91(2003) η~0 η~2.2

  7. The BRAHMS Experiment 7 Tracking Detectors Magnets

  8. 8 Charged hadron spectra AuAu @200 GeV [GeV/c]-2 [GeV/c]-2

  9. 9 system size dependence of p/π Eun-Joo Kim QM2005 BRAHMS Preliminary The transition point from soft to hard processes seems to shift to lower values for CuCu How about the dependence on the size of the actual interaction region?

  10. 10 Comparison of AuAu & CuCu Eun-Joo Kim, QM2005 BRAHMS Preliminary pbar to pion ratios in different collision systems are similar for comparable number of binary collisions

  11. 11 RCP dependence on  for AuAu @200 GeV and 62.4 GeV P. Staszel, QM2005 weak  dependence at 200 GeV…

  12. 12 Rcp in CuCu at = 62.4 GeV Similar suppression trend as in AuAu with respect to rapidity T. M. Larsen, QM2005 Negative and positive hadrons BRAHMS Preliminary

  13. 13 CuCu at @ 200 GeV : η = 3.2 Negative hadrons Spectra exhibit power law shape

  14. 14 CuCu at @ 200 GeV : η = 3.2 More suppression in central than peripheral collisions CuCu shows similar suppression pattern as AuAu

  15. 15 Summary • Suppression of high pt hadron production relative to binary scaling at h~3.2 in Au+Au collisions at sNN = 200 GeV • No strong rapidity dependence in suppression (0<y<3) • CuCu @ 62.4 GeV shows cronin like enhancement, but still there is a clear suppression as rapidity increases • CuCu @ 200 GeV shows clear supression more suppression in central than peripheral collisions similar behavior to AuAu at the same energy • pbar to pion ratios in different collision systems are similar for comparable number of binary collisions

  16. 16 BRAHMS Collaboration I.Arsene12, I.G. Bearden7, D. Beavis1, S.Bekele11, C. Besliu10, B. Budick6, H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, R.Clarke10, R.Debbe1, J. J. Gaardhøje7, K. Hagel8, H. Ito1, A. Jipa10, J. I. Jordre10, F. Jundt2, E.B.Johnson11, J.I.Jordre9, C.Jørgensen7, R. Karabowicz3, E. J. Kim11, T.M.Larsen7, J. H. Lee1, Y. K.Lee5, S.Lindal12, G. Løvhøjden2, Z. Majka3 , M. Murray11, J. Natowitz8, B.S.Nielsen7, D.Ouerdane7, R.Planeta3, F. Rami2, C.Ristea7, O.Ristea10, D. Röhrich9, B. H. Samset12, S. J. Sanders11, R.A.Sheetz1, P. Staszel3, T.S. Tveter12, F.Videbæk1, R. Wada8, H.Yang9, Z. Yin9,and I. S. Zgura10 1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Kracow, Poland 5Johns Hopkins University, Baltimore, USA, 6New York University, USA 7Niels 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 48 physicists from 12 institutions

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