1. GLOBAL EVENT FEATURES 1

2. Charged multiplicity (central collisions) Quantitative Difference from RHIC – dN ch /d  ~ 1600 ± 76 (syst) on high side of expectations growth with √s faster in AA than pp : (√s -‘nuclear amplification’ – Energy density ≈ 3 x RHIC (fixed  ) lower limit, likely    LHC) <    RHIC) PRL105 (2010) 252301 2 15 GeV/fm3 …….. or more

3. Bjorken’s formula A simple way to estimate the energy density from charged multiplicity or transverse energy measurements 3 HP: particle are produced at formation time  f (  f = 1 fm/c or less) Consider a slice of longitudinal thickness  z and section A This slice contains the particles with speed  And such a number can be expressed as: where we have used  ≈ y for    With some further calculations we get:

4. Charged multiplicity: centrality dependence dN ch /d  as function of centrality (normalised to ‘overlap volume’ ~ N participants ) – DPMJET MC fails to describe the data – HIJING MC strong centr. dependent gluon shadowing – Others saturation models: Color Glass Condensate, ‘geometrical scaling’ from HERA/ photonuclear react. DPMJET HIJING Important constraint for models sensitive to details of saturation Saturation Models Published on PRL

5. Interferometry - I Experimentally, the expansion rate and the spatial extent at decoupling are accessible via intensity interferometry, a technique which exploits the Bose– Einstein enhancement of identical bosons emitted close by in phasespace. This approach, known as Hanbury Brown–Twiss analysis 5 p

6. Interferometry - II The three-dimensional correlation functions can be fitted with the following expression, accounting for the Bose-Einstein enhancement and for the Coulomb interaction between the two particles: 6 = correlation strenght, k(q inv )= squared Coulomb wawefuntion PLB 696 (2011) Time at decoupling:  ̴ R out

7. System Size from pion interferometry 7  Spatial extent of the particle emitting source extracted from interferometry of identical bosons  Two-particle momentum correlations in 3 orth. directions -> HBT radii (Rlong, Rside, Rout)  Size: twice w.r.t. RHIC  Lifetime: 40% higher w.r.t. RHIC

8. Kaon interferometry 8 Kaon interferometry: complementary to pion due to different m T Results consisten with those with pions

9. Interferometry: pp vs Pb-Pb 9

10. Low-p T particle production 10 arXiv:1208.1974 [hep-ex] (low) p T spectra : superposition of collective motion of particles on top of thermal motion Collective motion is due to high pressure arising from compression and heating. “Blast-Wave” fit to p T spectra [1]:  Radial flow velocity ≈ 0.65 (10 % larger than at RHIC)  Kinetic freezout temp. T K ≈ 95 MeV (same as RHIC within errors) Central collisions: radial flow [1] E. Schnedermann, et al.; Phys. Rev. C48, 2462 (1993)

11. Particle yields and ratios 11 Assuming that the medium created in the collision reaches thermal equilibrium, one can compute particle yield and ratios with thermal models. Grand canonical ensamble: Where  =1/T and  i is the chemical potential Thermal models have been (and are being ) used to fit the measured particles yields (at different c.m. energies)  T and the baryochemical potential  b are free parameters to be obtained by the fit. N.B. T is the chemical freezout temperature……..

12. Yield and ratios at RHIC 12 !

13. Particle yields and ratios at LHC - Extracted from p T - integrated identified particle spectra. - Comparison /Fit with Thermal/ Statistical models work well at RHIC  info on chemical freezout temperature and baryochemical potential 13 Predicted temperature T=164 MeV A.Andronic, P.Braun-Munzinger, J.Stachel NP A772 167 Thermal fit (w/o res.): T=152 MeV (  2 /ndf = 40/9)  and  significantly higher than statistical model p/  and  /  ratios at LHC lower than RHIC Hadronic re-interactions ? F.Becattini et al. 1201.6349 J.Steinheimer et al. 1203.5302

14. ANISOTROPIC FLOW 14

15. Anisotropic flow: basic idea 15

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19. Elliptic flow 19 PxPx PyPy PzPz Reaction plane X Z Y  N ch yield

20. v 2 : selected ALICE results 20 v 2 for non-identified particles: v 2 for identified particles: Large elliptic flow oberved at RHIC  consistent with strongly coupled medium with low shear viscosity (ideal fluid) Stronger mass dependence of the elliptic flow as compared to RHIC:  Due to the larger radial flow?  Some deviation from hydrodynamic predictions for (anti) protons in close- to-central collisions: rescattering?

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22. 22 V2 scaling at RHIC

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27. More on anisotropic flow v 2 and v 3 over extended *  interval 27 V 3 sensitive to the fluctuations of the initial nucleon distribution *Results already published in the central  region: v 2  Phys. Rev. Lett. 105, 252302 (2010), v 3  Phys. Rev. Lett. 107, 032301 (2011)

28. HIGH-P T AND JETS 28

29. Particle spectra at high p T 29 Parton energy loss: A parton passing through the QCD medium undergoes energy loss which results in the suppression of high-p T hadron yields Related observable: nuclear modification factor R AA Reference: pp collisions Pb-Pb at different centralities

30. R AA for identified particles First measurement of (anti-)proton, K and  at high p T (>7 GeV/c) : – The R AA indicates strong suppression, confirming the indications from previous measurements for non-identified particles – The R AA for (anti-)protons, charged pions and K are compatible above ̴7 GeV/c  this suggests that the medium does not affect the fragmentation. 30

31. Charged jet: R AA and R CP 31 Strong jet suppression observed for jets reconstructed with charged particles – R AA (jet) is smaller than inclusive hadron R AA (h ± ) at similar parton p T – data are reasonably well described by JEWEL model K.Zapp, I.Krauss, U.Wiedemann, arXiv:1111.6838

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33. Near-side (jet-like) structure N.Armesto et al., PRL 93, 242301 33 Isolation of near-side peak:  –  correlation with trigger Long-range (large  ) correlation used as proxy for background   Evolution of near-side-peak   and   with centrality: Strong   increase for central collisions Interesting: AMPT describes the data very well Influence of flowing medium?