1. SQM 2008 Beijing, China 9.10.2008 L. Bravina (University of Oslo), A. Capella, E.G. Ferreiro,A.B.Kaidalov, K. Tywoniuk, E.Zabrodin

2. L. Bravina (University of Oslo), A. Capella, E.G. Ferreiro, A.B.Kaidalov, K. Tywoniuk, E.Zabrodin

3. 3 σ abs ~ 4-5 mb σ break-up ~ 1-2 mb Old data analyzed in Glauber model – what is the meaning of σ break-up ?? – need several nuclear targets

4. R AA @ RHIC = R AA @ SPS R AA @ Y=0 > R AA @ FORWARD 4

5. J/ Ψ SUPPRESSION OPEN CHARM SUPPRESSION 16.05.2008 5

6.  E<E C : rescattering of J/ ψ  absorption in nuclear medium  E>E C : J/ ψ is produced coherently  ”probe” modified nuclear gluon distribution  strong impact on AA observables @ RHIC, LHC  interacts with the ”medium”  suppression hint of large density  regeneration hint of thermal equilibium 6 Collaborators: A.B. Kaidalov, A. Capella, L. Bravina, E.G. Ferreiro, K.Tywoniuk, E. Zabrodin

7. COHERENT PARTONSHARD PROBES  x < x crit  shadowing  reduced multiplicity  small final state effects  thermalization?  coherent production  space time picture is complicated  x ≈ x crit  little shadowing  space-time picture is probabilistic model  rescattering  nuclear absorption  final state interactions  local in rapidity  local in b-space 7

8.  reggeon/pomeron exchange – multiperipheral model  the reggeon can be seen as an exchanged ladder of particles in the t-channel  a highly non-local object!  space-time picture  particle production from cuts 8 Amati, Fubini, Stanghellini Gribov

9.  ”classical” rescattering picture  coherence length of fluctuation:  large probability of rescattering  strong absorption effects  controlled by σ abs 9

10.  planar diagram vanishes at high energies  ladders require a long time to develop  critical x ~ 0.1  the projectile goes into a fluctuation long before the collision takes place  ladders develop at the same time 10 MandelstamGribov

11. 11  the diagrams corresponding to ”classical” rescatterings are suppressed at high energies!  Gribov trick: Glauber is OK after all! Almost...  have to take into account diffractive intermediate states! ++...

12. 12  Schwimmer model  good for ep, eA, pA  similiar to BK eq  similiar to eikonal diffractive structure function = ”Pomeron PDF” H1 2006 proton PDF CTEQ

13. 13 Arsene, Bravina, Kaidalov, Tywoniuk, Zabrodin PLB 657 (2007) 170 valid for x 2 GeV 2

14. planar diagrams non-planar  most of the observables do not feel the change of space-time picture  appears at high energy: nuclear shadowing  are there any observables that are sensitive to the transition? 14 E | Δσ 2 | total σ diffractive

15. absorption shadowing  critical scale depends on mass:  transition between  successive rescattering: nuclear absorption  coherent production: shadowing  happens around RHIC energies 15 E suppression total

16.  change of behaviour when increasing √s  α(x F =0) sensitive to changing initial-state  α(x F ≈1) has universal behaviour  x 2 scaling at high energies 16 α absorption energy-momentum conservation shadowing

17. 17 LHC will be free of LE effects! rapidity and centrality are under control σ abs =0 energy-momentum conservation!! Tywoniuk et al. PLB 660 (2008) 176 Capella, Ferreiro PRC 76 (2007) 064906

18.  rescattering → ”J/ψ’s fall apart”  what is the medium?  directly related to the multiplicity of the collision  not necessarily thermalized  interaction can take place with  ”partonic” medium – early times  hadronic medium – late times  the cross section should be averaged over p T distributions of colliding particles and time 18 finite energy effects - DPM Capella, Armesto, Ferreiro, Sousa, Kaidalov...

19.  Solving rate equation  Charmonium survival probabilty 19  natural from detailed balance  input from pp →  from NA50 fit:

20. 20  weaker comover suppression at forward  weaker recombination at forward  stronger initial state effects! Capella & Ferreiro, Phys. Rev. C76 (2007) 064906 Capella, Bravina, Ferreiro, Kaidalov, Tywoniuk, Zabrodin arxiv: 0712.4333

21. 21 Capella, Bravina, Ferreiro, Kaidalov, Tywoniuk, Zabrodin arxiv: 0712.4333 Recombination a small but important correction! Consistent with HSD with pre-hadron interaction Linnyk et al. arXiv:0801:4282

22.  large gluon shadowing  prediction: N co ~ 1800 at mid-rap  final state suppression ≈ @RHIC  σ (c c-bar) ~ s 0.3 ~ 1 mb @ LHC 22 initial state + final state y = 0

23.  thermalization of heavy quarks lead to opposite results!  NOTE:  no ”b-separation”  whole volume interacts!  strong dependence on pp cross section  doesn’t care about dA  suppression for Υ! 23 Andronic et al. NPA789(2007)334

24.  the large lever arm in energy can discriminate between different physical mechanisms  recombination wins in thermal eq. scenario  strong suppression in ”step-wise” comover interaction scenario  initial-state is non-trivial!  geometry...  less charmonium in ”pre-equilibrium” phase  thermalization can arise from highly coherent gluon field? 24

25. 25 The suppression of Y and Y¹ is calculated in the comovers model assuming a simple scaling relation of the comovers cross section with the onium, σ ~ r 2. The radii for Y and Y’ are taken from hep-ph/9610420: R Y =0.225 fm R Y¹ =0.509 fm R J/ψ =0.453 fm Comovers cross section leads to stronger suppression of Y’ than Y or J/ψ

26. 26 THANK YOU FOR YOUR ATTENTION!

27. 16.05.2008 27 Heavy ion event generator HYDJET++ (HYDrodynamics plus JETs) By: I.P. Lokhtin, L.V. Malinina, S.V. Petrushanko, A.M. Snigirev, I. Arsene, K. Tywoniuk hep-ph 0809.2708I.P. LokhtinL.V. MalininaS.V. PetrushankoA.M. SnigirevI. ArseneK. Tywoniuk0809.2708

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30. 16.05.2008 30 LHC SPS RHIC

31. SUPPRESSION OF HIGH-P T PARTICLES J/ Ψ SUPPRESSION  particles are not absorbed  possibility of soft interaction  p T shifted to smaller values  δp T ~ (p T - ‹p T ›) α  vansihes for bulk, soft particles  strong effect since spectra are steep  strong suppression  strong azimuthal asymmetry  non-flow effect!  absorption in normal, nuclear matter  controlled by σabs  present in pA and small AA systems  changes with rapidity  interaction with co-movers  controlled by σco → transformed into DD pair 16.05.2008 31

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