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

2 Nuclear modification factors Definitions R d(A)A  R CP –R d(A)A : isospin effects, canonical strangeness suppression –R CP : collective effects in peripheral collisions, undefined collision geometry in peripheral collisions R dAu = d 2 N/dp T d  (d+Au) N Coll d 2 N/dp T d  (p+p) R AA = d 2 N/dp T d  (A+A) N Coll d 2 N/dp T d  (p+p) R CP = N coll d 2 N/dp T d  (A+A) peripheral central

3 Kinematics RHIC example At 4° (y~3 for pions) and p T =1 GeV/c one can reach values as low of x 2 ~ This is a lower limit, not a typical value: most of the data collected at 4° would have x 2 ~0.01 Guzev, Strikman, and Vogelsang (hep-ph/ ) y=rapidity of (x L, k) system  1 process

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

5 Charged hadrons – R dAu at different pseudorapidities R dAu   d 2 N d+Au /dp T d  d 2 N pp inel /dp T d  <> = 7.2 where = 7.2±0.3 BRAHMS: PRL 93, (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) (R)

6 R dAu :  0 (  =4) STAR R dAu 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 Consistent with PHENIX at  = and STAR at  = Change of R CP from mid- to forward rapidities is stronger for central collisions than for semi-peripheral collisions BRAHMS: PRL 93, (2004) S.S.Adler et al. (PHENIX), Phys. Rev. Lett. 94 (2005) B. Mohanty (STAR), QM2005 (1B)

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

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

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

11 Experimental facts – dAu at RHIC (1) At midrapidity –Cronin enhancement observed for several particle species in R dAu and R CP –Magnitude differs by a factor of 2 –R CP (Cronin peak)  R dAu (Cronin peak) –Cronin effect (baryons) > Cronin effect (mesons) At forward rapidities –Increasing suppression of charged hadrons, h -,  -,  0, J/  with increasing (pseudo)rapidity –R CP : suppression of protons and antiprotons –R dAu : 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 p T P. Steinberg (PHOBOS), QM 2004 

13 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 dn/d  charged hadrons dAu 200 GeV dAu 19.4 GeV T. Alber et al. (NA35), Eur. Phys. J. C 2, 643 (1998) NA35

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

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

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

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

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

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

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

21 Phenomenological models (1) Suppression at large x F –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 x F  1 B. Kopeliovich et al., hep-ph/

22 Phenomenological models (2a) 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 K. Tywoniuk, I. Arsene, L. Bravina, A.B. Kaidalov, QM2005, poster 241 to get rid of non- shadowing contributions

23 Phenomenological models (2b) 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? K. Tywoniuk, I. Arsene, L. Bravina, A.B. Kaidalov QM2005, poster 241 NA49 data See also I.Vitev, 2005 RHIC&AGS Annual User’s Meeting; T.Goldman, M.Johnson, J.W.Qiu, I.Vitev, in preparation

24 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<E p <35GeV 35<E p <45GeV STAR preliminary

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

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

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

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

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

30 R AuAu : identified hadrons – Au+Au at 200 GeV midrapidity vs  =3.2 R. Karabowicz (BRAHMS), QM2005, section 1b NO change of R AuAu with rapidity pionsprotons

31 CGC + 3d-hydro + jet  CGC + 3d-hydro- dynamic simulation with jet (2  2 pQCD/ PYTHIA) PRC 68 (2003) Hirano and Nara Little change of R AuAu (pions) with rapidity

32 CGC + 3d-hydro + jet Why? PRC 68 (2003) Hirano and Nara 1.CGC initial parton distribution drops by a factor of 2 at  =3.2 2.Different time evolution of the thermalized parton density at  =3.2 → less jet energy loss 3.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 Conclusions (AuAu) Nuclear modification –Strong pion suppression at all rapidities –Protons are enhanced at all rapidities (R AuAu ) and moderate p T –No dependence of R AuAu on rapidity –Accidental effect? Surface emission? Outlook –Connection to flow R AA (pt,  )  = 0°  = 90°