Natalia KatryskaSmoluchowski Institute of PhysicsJagiellonian Universityfor the BRAHMS Collaboration

2Overview of BRAHMS detector setup.A few details of analysis process.Nuclear Modification Factor in d+Au collisions for different centralities and rapidities @ 200 GeV.4.Forward like-particle ratios of pions, kaons and protons @ 62.4 GeV and 200 GeV.5. The invariant yield distributions of identified hadrons.6. Limiting fragmentation in p+p collisions.7. Summary.

3STARPHOBOSPHENIX Colliding systems: @ 62.4 and 200 GeV Au+Au Cu+Cu d + Au p + pRICH detector situated in Forward Spectrometer allows to identify high momentum particles (e-,-/+, -/+, K-/+, p); ToF placed before RICH measures hadrons with lower velocity.

1. Particle identification of pions, kaons and protons.2. Applied corrections for: efficiency, weak-decays, absorption in materials .3. The data was corrected for geomet- rical acceptance.

5Nuclear medium effects:* Cronin enhancement for y ~ 0 ;* suppression at high p T ;* expected Color Glass Condensate state (gluon saturation) at forward rapidity (low x) ?PRL 93 (2004) 242303

6Although there is a limitation in pT to determine the nuclear modification factor at BRAHMS experiment the suppression of R d+Au is clearly visible for forward rapidities for pions, kaons and protons for 0-30% centrality bin. For peripheral centrality the value of factor is comparable with midrapidity region. At midrapidity, at pT 2 GeV/c , for both centralities R d+Au of protonos reaches value > 1.5.E.J.Kim, H.Yang, INCP2007

p + p collisions

p + p collisions @ 200 GeV The protons over antiprotons yield excess causes a noticeable difference between the p/- and p/+ . That high p/+ at high pT is a puzzle , especially with reference to the baryon number transport considering as a soft low pT phenomena.

p + p collisions The difference between protons and antiprotons yield seen @ 200 GeV, at lower energy increses by an order of the magnitude.

10p + p collisions A remarkable value for the p/ +(pT) ratio is observed at = 3.2 in p+ p collisions @ 62.4 GeV. This value is considerably different from the value measured @ 200 GeV. The increase of p/ with increasing y is seen in the wide range of rapidity.

11 factorization & normalization scales: F R pT ; CTEQ6 parton distribution functions; KKP modified to obtain FFs for specific charges: D+u = (1+z)D0u ; D0u = 1/2D- + +u ; z = fraction of the parton momentum carried by the hadron; D+u = function fragmenting u quarks into positive pions; AKK - FFs reproduce well STAR data at y~0 => at high y: gluons fragmenting into anti-/protons > 80% for pT < 5 GeV/c; p + p collisions @ 200 GeVPRL 98 (2007) 252001

12 factorization & normalization scales: F R pT ; KKP modified as for p+p system @ 200 GeV; observed rapid changes with different rapidities at high pT (xF up to 0.5); although at high pT it seems that the fit falls down below data there is still good agreement; F. Videbaek, Winter Workshop on Nuclear Dynamics, 2007p + p collisions @ 62.4 GeV

13J. Phys. G: Part. Phys. 8 August 2007 S619-S622

14 Going from midrapidity to forward rapidity there is no sigificant alteration - taking errors under consideration - for the most central d+Au collisions.

For more peripherial reactions for rapidity y ~ 3 it is noticeable the difference of proton and antiproton production in comparison with midrapidity regime.H. Yang, QM2008, oral presentaion

15 A remarkable overlap of dN/dy distributions at all energies (p+p @ 200 GeV, ybeam ~ 5.3; p+p @ 62.4 GeV, ybeam ~ 4.2) appears when viewed in their projectile frame.

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* It is observed a significant suppression of the yield of charged hadrons compared to p+p collisions at forward rapidities. * Due to limitation in pT it is difficult to specify the character of particular particle in forward regime.

* The results @ 200 GeV indicate that the simple quark-diquark breaking mechanism is not sufficient to characterize particles yields in the whole considered interval of rapidity. * It seems that NLO pQCD rationally describe the mesons (pions and kaons) production distributions at high rapidity in relativistic elementary collisions.* The updated AKK FFs reflect the invariant cross section for anti-/proton ; the unexpected excess of protons over antiprotons (p/p ~ 0.1 at y ~3.3) yield suggests it may not be related to baryon transport number.* Forward particle production @ 62.4 GeV has a similar tendency, but with stronger effect. d+Au collisions: p+p collisions:

17I. C. Arsene12, I. G. Bearden7, D. Beavis1, S. Bekele12, C. Besliu10, B. Budick6, H. Bggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, H.Dahlsgaard7, R. Debbe1, J. J. Gaardhje7, K. Hagel8, H. Ito1, A. Jipa10, E.B.Johnson11, J. I. Jrdre9, C. E. Jrgensen7, R. Karabowicz5, N. Katrynska5 ,E. J. Kim11, T. M. Larsen7, J. H. Lee1, Y. K. Lee4,S. Lindahl12, G. Lvhiden12, Z. Majka5, M. J. Murray11,J. Natowitz8, C.Nygaard7, B. S. Nielsen7, D. Ouerdane7, D.Pal12, F. Rami3, C. Ristea8, O. Ristea11, D. Rhrich9, B. H. Samset12, S. J. Sanders11, R. A. Scheetz1, P. Staszel5, T. S. Tveter12, F. Videbk1, R. Wada8, H. Yang9, Z. Yin9, I. S. Zgura2 , A. Qviller7

1. Brookhaven National Laboratory, Upton, New York, USA2. Institute of Space Science, Bucharest - Magurele, Romania3. Institut Pluridisciplinaire Hubert Curien et Universit Louis Pasteur, Strasbourg, France4. Johns Hopkins University, Baltimore, USA5. M. Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland6. New York University, New York, USA7. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark8. Texas A&M University, College Station, Texas, USA9. University of Bergen, Department of Physics and Technology, Bergen, Norway10. University of Bucharest, Romania11. University of Kansas, Lawrence, Kansas, USA12. University of Oslo, Department of Physics, Oslo, Norway

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19 * at = 0 central-peripheral ratio larger than semicentral-peripheral: increased role of Cronin-like multiple scattering effects ;* at = 3.2 more central ratio is lower: suppression mechanism depends on the centraliy collision;PRL 93 (2004) 242303

20 Viewing from the rest frame of one of the nuclei with simultaneously substracting calculated value of target baryons (grey bands) for heavy ions collisions at RHIC (BRAHMS) and SPS (NA49).