1. Suppression and Azimuthal asymmetry of particle production in heavy-ion collisions
Konrad Tywoniuk
University of Oslo
Collaborators: A. Capella
E.G. Ferreiro
A.B. Kaidalov
XLIII Recontres de Moriond – QCD and High Energy Interactions

2. XLIII Recontres de Moriond
Intimate connection?
Matter is opaque – strong suppression
There is a large azimuthal asymmetry of the suppression
Particles ”flow”...
Flow saturates where suppression saturates!
XLIII Recontres de Moriond

3. RHIC: the party line scenario
Reaction
plane x z y
Matter formed in the collsion is a perfect liquid with (almost) no viscosity
Hydrodynamical picture works
Initial eccentricity is effectively transformed into momentum anisotropy of final state particles
Jets that traverse the thermalized medium radiates
energy loss ~ρL2
Thermalization is reached within 0.5 fm after the initial moment of collision
Is it possible to formulate a model without these assumptions that give the same experimental features?
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4. Comover scenario
Small interaction cross sections (σ ~ 1 mb) in the final state
φ enhancement
J/ψ suppression
high-pT particle suppression
Based on rate equations – does not rely on thermlization assumption
Capella, Ferreiro, Kaidalov, Sousa EPJC40(2005)129
Capella, Ferreiro EPJC42(2005)419;
Capella et al. arXiv:
Capella, Salgado PRC60(1999)054906
Azimuthal dependence can easily be introduced!
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5. XLIII Recontres de Moriond
Results with σ ~ 1 mb
Capella, Ferreiro EPJC42(2005)419
Centrality and azimuthal angle dependence of RAA is also ok!
centrality dependence of v2 is ok!
Mass dependence of elliptic flow comes naturally...
XLIII Recontres de Moriond

6. Predicitions for LHC and outlook
Heavy Ion Collisions at the LHC - Last Call for Predictions: arXiv:  [hep-ph]
calculations for v2 at LHC are being computed for realistic case
RAA(Δφ) is well reproduced!
LHC ~ 1.5 RHIC
due to strong final state suppression
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7. XLIII Recontres de Moriond
Backup I
New method of calculating the suppression along the path of the particle
Can check dijet correlations
Zhang, Owens, Wang, Wang PRL98(2007)212301
XLIII Recontres de Moriond

8. Backup II: Is the matter at RHIC strongly or weakly interacting?
Bhalerao, Blaizot, Borghini, Ollitrault PLB627(2005)49
Is thermalization reached?
v4/v22 ~ 1  0.5 is a hydro prediction
no saturation of v2/ε with density (dN/dy/S)
Inverse Knudsen number ~ 2
Hints of small final state interactions that only affect rare processes
<pT> unchanged going from central to peripheral (~20% , compatible with pA)
weak centrality dependence of (Anti-p, Λ, Ξ,Ω)/h-
Saturation expected from thermalized system
No decrease in <pT2> for J/ψ in central collisions
High-pT particles come dominantly from jet fragmentation in vacuum?
Drees, Feng, Jia PRC71(2005)034909
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