Identified hadron production in d+Au and p+p collisions at RHIC

1. Identified hadron production in d+Au and p+p collisions at RHIC Hongyan Yang for the BRAHMS Collaboration University of Bergen, Norway

2. Outline • Experimental overview • Preliminary results - particle spectra- particle yields and ratios- nuclear modification factor- net-protons • Summary Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

3. Motivations • rapidity dependence of particle spectra in p+p and d+Au: a reference for heavy ion collisions • particle spectra in p+p collisions: a test of pQCD • nuclear modification factor for nuclear effect, initial state effect? • rapidity distribution of net-protons: stopping in elementary collisions Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

4. Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

5. Identified particle spectra in p+p collisions Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

6. Calculations by W. Vogelsang Spectra at forward rapidity (pp collisions) – comparison to NLO pQCD BRAHMS Preliminary Same fragmentation functions as used for the PHENIX comparison at mid-rapidity. mKKP: KKP has only 0 fragmentation. Modifications were needed to calculate charged pions. K: fragmentation function by Kretzer • NLO pQCD describes data also at forward rapidities Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

7. BRAHMS Preliminary Red: p/+Blue: p-bar/ - e+e-: p+p-bar/++ - (ALEPH) Spectra at forward rapidity ( p+p collisions ) pT-dependence of ratios Ratios y=3.0 and 3.3 • Excess of positive pions: ratio ->1/2 (valence quark counting) • Small p/p ratio eliminates possible strong g -> p or p fragmentation • The difference between protons and anti-protons indicates another mechanism besides fragmentation that puts so many protons at high pT. Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

8. PRL 93, 242303 (2004) RdAu - for hadrons, suppression was seen at forward rapidity - Pions are suppressed, while protons are not Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

9. d2N/2ppTdpTdy Extraction of particle yields (p+p) Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

10. Rapidity distributions Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

11. like-particle ratios (p+p) Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

12. K/p, p/p ratios (p+p) Open symbols: positive particles Closed symbols: negative particles All ratios decrease with increasing rapidity , except p/p+ Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

13. dN/dpT BRAHMS Preliminary p+p 200GeV pT [GeV/c] Net-proton distribution • Subtraction of p-bar yield from proton yield for each pT bin • A Boltzmann function is used to fit the data Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

14. p+p 200GeV Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

15. d+Au 200GeV Net-proton distribution (d+Au) Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

16. Summary • NLO pQCD describes pT spectra at forward rapidities in p+p collisions • RdAu: suppression of h- yields at forward rapidities confirmed by identified hadrons spectra • Strong suppression of pions • No suppression of protons • HIJING/B describes the net-protons in p+p better than PYTHIA • Net-protons are piled up at mid-rapidity in central d+Au collisions Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

17. BRAHMS Collaboration I. C. Arsene12, I. G. Bearden7, D. Beavis1, S. Bekele12, C. Besliu10, B. Budick6, H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, H.Dahlsgaard7, R. Debbe1, J. J. Gaardhøje7, K. Hagel8, H. Ito1, A. Jipa10, E.B.Johnson11, J. I. Jørdre9, C. E. Jørgensen7, R. Karabowicz5, N. Katrynska5 ,E. J. Kim11, T. M. Larsen7, J. H. Lee1, Y. K. Lee4,S. Lindahl12, G. Løvhøiden12, Z. Majka5, M. J. Murray11, J. Natowitz8, C.Nygaard7B. S. Nielsen8, D. Ouerdane8, D.Pal12, F. Rami3, C. Ristea8, O. Ristea11, D. Röhrich9, B. H. Samset12, S. J. Sanders11, R. A. Scheetz1, P. Staszel5, T. S. Tveter12, F. Videbæk1, R. Wada8, H. Yang9, Z. Yin9, I. S. Zgura2 1. Brookhaven National Laboratory, Upton, New York, USA 2. Institute of Space Science, Bucharest - Magurele, Romania 3. Institut Pluridisciplinaire Hubert Curien et Université Louis Pasteur, Strasbourg, France 4. Johns Hopkins University, Baltimore, USA 5. M. Smoluchkowski Institute of Physics, Jagiellonian University, Krakow, Poland 6. New York University, New York, USA 7. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark 8. Texas A&M University, College Station, Texas, USA 9. University of Bergen, Department of Physics and Technology, Bergen, Norway 10. University of Bucharest, Romania 11. University of Kansas, Lawrence, Kansas, USA 12. University of Oslo, Department of Physics, Oslo, Norway Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

18. Backup slides Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

19. MRS by TOFW FS by RICH Particle Identification • Two plots (just flash...)- one is for MRS (TOFW)- another is for FS (RICH) Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)