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Midrapidity vs forward rapidities Nuclear modification factors R AA and R CP

Nuclear modification factors at forward rapidities. Dieter Roehrich University of Bergen. Midrapidity vs forward rapidities Nuclear modification factors R AA and R CP charged hadrons identified particles ( , p) dAu Au+Au, Cu+Cu. d 2 N/dp T d  (d+Au). d 2 N/dp T d  (A+A).

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Midrapidity vs forward rapidities Nuclear modification factors R AA and R CP

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  1. Nuclear modification factors at forward rapidities Dieter Roehrich University of Bergen • Midrapidity vs forward rapidities • Nuclear modification factors RAA and RCP • charged hadrons • identified particles (, p) • dAu • Au+Au, Cu+Cu

  2. d2N/dpTd (d+Au) d2N/dpTd (A+A) Ncoll d2N/dpTd (A+A) RdAu = RAA = RCP = NColld2N/dpTd (p+p) NColld2N/dpTd (p+p) Ncoll d2N/dpTd (A+A) Nuclear modification factors • Definitions • Rd(A)A  RCP • Rd(A)A: isospin effects, canonical strangeness suppression • RCP : collective effects in peripheral collisions, undefined collision geometry in peripheral collisions central peripheral peripheral central

  3. 108 106 104 102 100 M2 (GeV2) 10-6 10-4 10-2 100 x Kinematics 1 RHIC example • At 4° (y~3 for pions) and pT=1 GeV/c one can reach values as low of x2 ~ 10-4 • This is a lower limit, not a typical value: most of the data collected at 4° would have x2~0.01 21 process y=rapidity of (xL, k) system 2 Guzev, Strikman, and Vogelsang (hep-ph/0407201)

  4. BRAHMS Reference: pp midrapidity forward rapidities • NLO pQCD calc. (W. Vogelsang) h-

  5. 1 d2Nd+Au/dpTdh RdAu= <Ncoll> d2Nppinel/dpTdh where < Ncoll> = 7.2±0.3 Charged hadrons – RdAu at different pseudorapidities BRAHMS: PRL 93, 242303 (2004) • Cronin-like enhancement at =0 • Consistent with PHOBOS at =1 • Clear suppression as  changes from 0 to 3.2 PHOBOS, PHYS. REV. C70 (2004) 061901(R)

  6. RdAu: 0 (=4) STAR • RdAu at high  • Strong suppression • Larger than h- - isospin effect G.Rakness (STAR), DIS 2005

  7. Charged hadrons – centrality dependence of enhancement/suppression in d+Au BRAHMS: PRL 93, 242303 (2004) • Consistent with PHENIX at =1.4-2.2 and STAR at =2.5-4.0 • Change of RCPfrom mid- to forward rapidities is stronger for central collisions than for semi-peripheral collisions S.S.Adler et al. (PHENIX), Phys. Rev. Lett. 94 (2005) 082302 B. Mohanty (STAR), QM2005 (1B)

  8. RdAu and RCP(dAu): pions, (y=0) • RdAu : • Almost no Cronin effect • RdAu consistent with 1 • RCP: • Strong Cronin effect  0 M. Tannenbaum (PHENIX), 2005 RHIC&AGS Annual User’s Meeting K. Adcox et al. (PHENIX), Nucl. Phys. A757 (2005) 184

  9. RdA RdAu and RCP(dAu): pions and protons (y=0) • RdAu and RCP show Cronin effect • Effect seems to be larger for baryons than for mesons C. Mironov (STAR), 2005 RHIC&AGS Annual User’s Meeting and D.Pal (PHENIX), QM2005, sect. 1a

  10. BRAHMS preliminary RdAu and RCP(dAu): pions and protons (y=3.2) • RdAu • Strong suppression for - • Enhancement for antiprotons  different from RCP • RCP • Suppression for both pions and protons at forward rapidity BRAHMS preliminary F. Videbaek (BRAHMS), DIS2005  p H. Yang (BRAHMS), QM2005 (poster 36)

  11. Experimental facts – dAu at RHIC (1) • At midrapidity • Cronin enhancement observed for several particle species in RdAu and RCP • Magnitude differs by a factor of 2 • RCP(Cronin peak)  RdAu(Cronin peak) • Cronin effect (baryons) > Cronin effect (mesons) • At forward rapidities • Increasing suppression of charged hadrons, h-, -, 0, J/ with increasing (pseudo)rapidity • RCP : suppression of protons and antiprotons • RdAu: enhancement of antiprotons

  12. Experimental facts – dAu at RHIC (2) Ratio of dn/d(dAu) / dn/d(pp) exhibits a similar suppression trend • Enhanced production for  < 0 • Suppression for  > 0 • Modification effects all pions, not only at high pT P. Steinberg (PHOBOS), QM 2004 

  13. charged hadrons dAu 200 GeV dn/d dAu 19.4 GeV Experimental facts – dAu at SPS (1) • Enhanced production for  < 0 • Suppression for  > 0 • Limiting fragmentation Ratio of dn/dy(dAu) / dn/dy(NN) exhibits a similar suppression trend NA35 T. Alber et al. (NA35), Eur. Phys. J. C 2, 643 (1998)

  14. d2N(h-)/dpTdy (d+Au) RdAu = NColld2N(-)/dpTdy (p+p) Experimental facts – dAu (pPb) at SPS (2) dAu B. Boimska (NA49), PhD thesis, Warzaw (2004) • Increasing suppression with increasing xF • Pattern similar for pions and antiprotons, different for protons pPb Similar trend at the AGS: R. Debbe et al. (BRAHMS) CINPP proceedings (2005)

  15. Stopping and particle production in p(d)-A at SPS • Large momentum degradation of projectile in central pA by multiple collisions • Very different from pp S. Brodsky et al., PRL 39 (1977) 1120 NA49 NA35 • Pion production at forward rapidities independent of target

  16. r/ ggg Anti Shadowing Shadowing Initial and final effects - dAu • Initial effects • Wang, Levai, Kopeliovich, Accardi • Especially at forward rapidities: • Eskola, Kolhinen, Vogt, Nucl. Phys. A696 (2001) 729-746 • HIJING • D.Kharzeev et al., PLB 561 (2003) 93 • Others • B. Kopeliovich et al., hep-ph/0501260 • J. Qiu, I, Vitev,hep-ph/0405068 • R. Hwa et al., nucl-th/0410111 • D.E. Kahana, S. Kahana, nucl-th/0406074 “Cronin effect” Initial state elastic multiple scattering leading to Cronin enhancement (RAA>1) broaden pT Nuclear shadowing depletion of low-x partons Gluon saturation depletion of low-x gluons due to gluon fusion ”Color Glass Condensate (CGC)” Suppression due to dominance of projectile valence quarks, energy loss, coherent multiple scattering, energy conservation, parton recombination, ...

  17. CGC saturation model (1) • CGC describes dn/d and 0 inv. CS at forward rapidities Data: BRAHMS, submitted to PRL, nucl-ex/0401025 Data: B. Mohanty (STAR), QM2005 Model: A. Dumitru, A. Hayashigaki, J. Jalilian-Marian, hep-ph/0506308 Model: Kharzeev, Levin, Nardi. Nucl. Phys. A 730 (2004) 448

  18. CGC saturation model (2) • CGC model describes RdAu and RCP • Suppression comes in at y > 0.6 D. Kharzeev, Y.V. Kovchegov, K. Tuchin, hep-ph/0405054 (2004)

  19. pQCD models (1) • pQCD-improved parton model • Glauber-type collision geometry • Nuclear shadowing • Initial state incoherent multiple scattering G.G. Barnafoldi, G. Papp, P. Levai, G. Fai, nucl-th/0404012 (2004) see also A. Arcadi, M. Gyulasy, nucl-th/0402101 (2004) • Increasing strength of standard nuclear shadowing with increasing  •  reasonable agreement between RdAu and pQCD • but underestimation of centrality dependence of RCP see R. Vogt, hep-ph/0405060 (2004), Phys.Rev. C70 (2004) 064902 See also R. Vogt, hep-ph/0405060 (2004)

  20. pQCD models (2) • Coherent multiple scattering of a parton with the remnants of thenucleus in the final state J.W.Qiu, I.Vitev, hep-ph/0405068 • Low pT suppression which grows with rapidity and centrality • Disappearence of the nuclear modification at high pT

  21. Phenomenological models (1) • Suppression at large xF • Forward region is dominated by the fragmentation of valence quarks • Induced energy loss via increased gluon bremsstrahlung in cold nuclear matter • Momentum conservation forbids particle production at xF 1 B. Kopeliovich et al., hep-ph/0501260

  22. to get rid of non-shadowing contributions Phenomenological models (2a) K. Tywoniuk, I. Arsene, L. Bravina, A.B. Kaidalov, QM2005, poster 241 • Gluonic shadowing in GRIBOV-REGGE FIELD THEORY • GRFT links shadowing in A-A collisions to diffraction • Input: data from H1 and ZEUS on diffraction (NLO QCD) → gluonic nPDF • Assumptions: • high-pT particles come from jets • no rapidity dependence in Cronin effect • Result: Suppression at forward rapidities is mostly due to gluonic shadowing

  23. Phenomenological models (2b) NA49 data K. Tywoniuk, I. Arsene, L. Bravina, A.B. Kaidalov QM2005, poster 241 • Gluonic shadowing in GRIBOV-REGGE FIELD THEORY at SPS • Although present at SPS energies, gluonic shadowing cannot explain the magnitude of the effect • Shadowing due to valence quarks will dominate in this kinematical region • Final state multiple scattering and energy loss? See also I.Vitev, 2005 RHIC&AGS Annual User’s Meeting; T.Goldman, M.Johnson, J.W.Qiu, I.Vitev, in preparation

  24. 25<Ep<35GeV STAR preliminary 35<Ep<45GeV Conclusions (dAu) • Cronin effect • Experimental situation needs clarification • Initial or final state effect? • Suppression phenomena at RHIC and SPS • Variety of processes can result in suppression • Quality of data is insufficient for ruling out models • Outlook • Back-to-back azimuthal correlations with large  • Low energy dAu run at RHIC – a unique chance

  25. Final state effects – A+A collisions • Gallmeisteret al., PRC67(2003)044905 • Fries, Muller, Nonaka, Bass,nucl-th/0301078Lin, Ko,PRL89(2002)202302 • R. Hwa et al., nucl-th/0501054 • Gyulassy, Wang, Vitev, Baier, Wiedemann… • e.g. nucl-th/0302077 Hadronic absorption of fragments Parton recombination (up to moderate pT) Energy loss of partons in dense matter

  26. RAA: 0, and direct photons - AuAu at 200 GeV (y=0) PHENIX • Direct photons: no suppression • Large suppression for 0, in central AuAu at high pT B. Cole (PHENIX), QM2005

  27. 0-5% Au+Au p+p STAR Preliminary RAuAu vs RCP: identified hadrons – AuAu at 200 GeV (y=0) • RAuAu • baryons are enhanced • mesons are suppressed • RCP • baryons suppressed > 2.5 GeV/c • mesons suppressed > 1.5 GeV/c J. Dunlop (STAR), QM2005

  28. 62.4 ”SPS”-like hadron chemistry radial flow drops by 30% 62.4 Matter at forward rapidity (y3) dn/dy drops by a factor of 3 BRAHMS, Phys. Rev. Lett. 94(2005) 162301 J.I. Jørdre (BRAHMS), PhD thesis (2004) I. Arsene (BRAHMS), QM2005, poster 126

  29. RCP vs RAuAu : identified hadrons – Au+Au at 200 GeV (=3.2) • Large difference in RAuAu vs RCP for (anti-)protons • RAuAu mass dependence • RCP constant suppression R. Karabowicz (BRAHMS), QM2005, section 1b

  30. NOchange of RAuAu with rapidity RAuAu: identified hadrons – Au+Au at 200 GeV midrapidity vs =3.2 pions protons R. Karabowicz (BRAHMS), QM2005, section 1b

  31. CGC + 3d-hydro + jet • CGC + 3d-hydro-dynamic simulation with jet (22 pQCD/ PYTHIA) PRC 68 (2003) Hirano and Nara • Littlechange of RAuAu(pions) with rapidity

  32. CGC + 3d-hydro + jet Why? PRC 68 (2003) Hirano and Nara • CGC initial parton distribution drops by a factor of 2 at =3.2 • Different time evolution of the thermalized parton density at =3.2 → less jet energy loss • Steeper slope of pQCD components at =3.2 Is 2. cancelled by 3. ?

  33. Surface emission • Medium at RHIC is so dense that only particles produced close to the surface can escape • Can corona effect mask the lower parton density at =3.2 ? Dainese, Loizides, Paic, Eur. Phys. J. C38 (2005) 461

  34. Df = 90° Df = 0° Conclusions (AuAu) • Nuclear modification • Strong pion suppression at all rapidities • Protons are enhanced at all rapidities (RAuAu) and moderate pT • No dependence of RAuAu on rapidity • Accidental effect? Surface emission? • Outlook • Connection to flowRAA(pt, )

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