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ALICE overview

ALICE overview. Francesco Prino INFN – Sezione di Torino On behalf of the ALICE collaboration. SQM2011, Cracow, September 19 th 2011. Muon Arm -4 < h < - 2.5. Central Barrel Tracking, PID h < 0.9. Alice numbers: 1300 members 116 institutes 33 countries.

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ALICE overview

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  1. ALICE overview Francesco Prino INFN – Sezione di Torino On behalf of the ALICE collaboration SQM2011, Cracow, September 19th 2011

  2. Muon Arm -4 < h < -2.5 Central Barrel Tracking, PID h < 0.9 Alice numbers: 1300 members 116 institutes 33 countries

  3. Data samples, statistics • Triggers • MB: based on VZERO (A and C) and SPD • SINGLE MUON: fowardmuon in coincidence with MB trigger • Centrality selection in PbPb • Amplitudes in the V0 scintillators • reproduced by Glauber model fit PRL106 (2011) 032301

  4. Global event features

  5. Charged particle multiplicity • dNch/dh = 1584  76 • (dNch/dh)/(Npart/2) = 8.3  0.4 • ≈ 2.1 x central AuAuat √sNN=0.2 TeV • ≈ 1.9 x pp (NSD) at √s=2.36 TeV • Stronger rise with √s in AA w.r.t. pp • Stronger rise with √s in AA w.r.t.log extrapolation from lower energies • Very similar centrality dependence at LHC & RHIC • After scaling RHIC results (x2.1) to the multiplicity of central collisions at the LHC PRL106 (2011) 032301 PRL105 (2010) 252301 P. Petrov, Parallel, Tue 20, 14:00

  6. System size ALICE: PLB696 (2011) 328 ALICE: PLB696 (2011) 328 • Spatial extent of the particle emitting source extracted from interferometry of identical bosons • Two-particle momentum correlations in 3 orthogonal directions -> HBT radii (Rlong, Rside, Rout) • Size: twice w.r.t. RHIC • Lifetime: 40% higher w.r.t. RHIC

  7. System size vs. multiplicity NEW FOR SQM • HBT radii scale linearly with multiplicity1/3 in pp and PbPb • HBT radii in PbPb vs. trend from lower energy AA: • Rlong: perfectly agree • Rside: reasonably agree • Rout: clearly below the trend • Behaviour of all 3 radii in qualitative agreement with hydro expectations • Rout/Rside decreases with √s due to higher initial temperature

  8. Collective expansion y x y x R. Preghenella, Plenary, Mon 14:00

  9. Identified hadron spectra • Combined analysis with ITS, TPC and TOF • Lines = blast-wave fits to extract • Integrated Yields • Average pT • Parameters of the system at the thermal freeze-out B. Guerzoni, Parallel, Tue 20, 14:20

  10. , K, p spectra and collective radial expansion • Significant change in mean pTbetween √sNN=200 GeV and 2.76 TeV • Harder spectra. • For the same dN/dh higher mean pT than at RHIC • Common blast-wave fit to , K and p • Strong radial flow: b≈0.66 for most central collisions • 10% higher than at RHIC • Larger w.r.t. hydro predictions Centrality STAR pp √s=200 GeV Blast-wave fit parameters B. Guerzoni, Parallel, Tue 20, 14:20

  11. Elliptic flow • At LHC, pT integrated v2increases by 30% w.r.t RHIC data at √sNN=200 GeV PRL 105 (2010) 252302

  12. pt differential elliptic flow • v2 vs. pT does not change within uncertainties between √sNN=200 GeV and 2.76 TeV • 30% increase of pT integrated flow explained by higher mean pT due to stronger radial flow at higher energies • Significant values of v2 for pT>8 GeV/c • Due to path length dependence of parton energy loss PRL 105 (2010) 252302

  13. Identified particle v2 F. Noferini, Parallel, Tue 20, 17:50 • Stronger radial flow -> more pronounced mass dependence of elliptic flow • Hydrodynamics predictions describe well the measured v2(pT) for  and K for semi-peripheral (40%-50%) and semi-central (10%-20%) collisions • Mismatch for anti-protons in the more central bin • Larger radial flow in the data than in the Hydro model • Rescatterings in the hadronic phase play an important role (arXiv:1108.5323)

  14. Higher harmonics arXiv:1105.3865 yRP y2 • Fluctuations in the initial nucleon distribution • Event-by-event fluctuation of the symmetry plane n w.r.t. RP • Odd harmonics are not null • v3(“triangular”) harmonic: • v3has weaker centrality dependence than v2 • When calculated w.r.t. participant plane, v3vanishes (as expected, if due to fluctuations) • Similar pT dependence for all harmonics • v3 sensitive to shear viscosity h/s and to assumption on initial parton density y3 Y. Zhou, Parallel, Fri 23, 14:20

  15. Di-hadron correlations • Higher pT • Near-side jet dominates • Quenching/suppression and broadening of the away side jet • Lower pT • Near-side ridge • First observed at RHIC • Observed also by CMS in high multiplicity pp collisions at √s=7 TeV • Broad away-side • Dominated by hydrodynamics and flow arXiv:1109.2501

  16. Fourier analysis • Extract 1D  correlations by integrating the C(,) in 0.8<||<1.8 range and do a Fourier decomposition • 5 components describe completely the correlations at large  and low pT • Strong near-side ridge + double-peaked structure on away side arXiv:1109.2501

  17. Due to collective flow? • If observed di-hadron correlation comes from collective flow: • vnD come from correlation with a common plane of symmetry (Yn) • Test factorization with global fit to vnD vs. pTtrig and pTassoc • If it matches data -> indication for flow-type correlations • Result: • Good description at low pT • Does not work at high pT arXiv:1109.2501

  18. Due to collective flow? • If observed di-hadron correlation comes from collective flow: • vnD come from correlation with a common plane of symmetry (Yn) • Test factorization with global fit to vnD vs. pTtrig and pTassoc • Compare with vn from elliptic flow analysis -> OK arXiv:1109.2501

  19. Strangeness production and chemical composition B. Hippolyte, Plenary, Wed 9:30

  20. Baryon to meson ratio: L/Ks0 P. Kalinak, Parallel, Tue 20, 15:40 • Baryons more abundant at intermediate pT • Baryon/meson ratio increases with centrality • Consistent with recombination • Enhancement stronger than at RHIC • Maximum of L/K slightly pushed towards higher pT than at RHIC • higher radial flow?

  21. Multi-strange baryons NEW FOR SQM Text M. Nicassio, Parallel, Tue 20, 18:10

  22. Comparison with thermal model A. Kalweit, Parallel, Tue 20, 16:30 NEW FOR SQM • All yields, except protons, follow thermal model prediction for grand-canonical ensemble and Tch=164 MeV • Measured proton/pion ratio below thermal model expectation • Strange particles perfectly agree with thermal model expectation

  23. Strangeness production: AA vs. pp NEW FOR SQM Production of multi-strange baryons in PbPb collisions at √s=2.76 TeV enhanced with respect to pp

  24. Strangeness production: AA vs. pp NEW FOR SQM • Comparison with results at lower energies (SPS, RHIC) • The enhancement of strange baryons decreases with √s • Strange /non-strange ratio • Constant vs. √s in AA above SPS energy • Increases with √s in pp

  25. Parton energy loss in the medium Jet J. Otwinowski, Plenary, Wed, 12:30

  26. Charged hadron RAA: ingredients • pT spectra in PbPb • pT reach 50 GeV/c • Shape of pTdistribution changes with centrality • pp reference • from ALICE pp measurements at √s=0.9, 2.76 and 7 TeV

  27. Charged hadron RAA NEW FOR SQM • RAA(pT) for charged particles: • Suppression increases with increasing centrality • Minimum for pT~ 6-7 GeV/c in all centrality classes • RAA increases in the region pT>10 GeV/c • Hint of flattening above 30 GeV/c

  28. RAA for p+,p- and p0 • Identification of p+ and p- from dE/dx relativistic rise in TPC • p0 from g conversions • Same suppression for p0 and p • p vs. charged particles: • Effect of baryon enhancement for pT<5-6 GeV/c

  29. RAA for L and Ks0 S. Schuchmann, Parallel, Tue 15:40 • Ks0 behave as charged particles • Suppression of L: • At high pT similar to charged particles • Baryon enhancement at low pT • Different between RHIC and LHC: • Baryon/Meson enhancement • Canonical suppression • Energy loss

  30. Heavy flavours K p e,m D n e,m D D B J. Castillo, Plenary, Mon 16:30

  31. D mesons K p • Analysis strategy • Invariant mass analysis of fully reconstructed decay topologies displaced from the primary vertex • Feed down from B (10-15 % after cuts) subtracted using FONLL • Plus in PbPb hypothesis on RAA of D from B NEW FOR SQM D+K-p+p+

  32. D meson RAA A. Grelli, Parallel, Fri 16:50 D* RAA NEW FOR SQM • pp reference from measured D0, D+ and D* pTdifferential cross-sections at 7 TeV scaled to 2.76 TeV with FONLL • Suppression of prompt D mesons in central (0-20%) PbPb collisions by a factor 4-5 for pT>5 GeV/c • Little shadowing at high pT suppression is a hot matter effect • Similar suppression for D mesons and pions • Maybe a hint of RAAD > RAAπ at low pT

  33. D0 elliptic flow • First direct measurement of D flow in heavy-ion collisions • Yield extracted from invariant mass spectra of Kp candidates in 2 bins of azimuthal angle relative to the event plane NEW FOR SQM C. Bianchin, Parallel, Tue 18:10

  34. Heavy flavour decay electrons e • Cocktail method • Inclusive electron pT spectrum • Electron PID from TOF+TPC • TRD used in pp • Subtract cocktail of known background sources • Impact parameter method (only in pp for now) • Track impact parameter cut to select electrons from beauty R. Bailhache, Parallel, Tue 15:20

  35. Cocktail-subtracted electron RAA • pp reference from measured heavy flavour electrons pT differential cross-sections at 7 TeV scaled to 2.76 TeV with FONLL • Analysis of pp data at 2.76 TeV ongoing (will providE direct reference) • Suppression of cocktail-subtracted electrons • Factor 1.5 - 4 for pT>3.5 GeV/c in the most central (0-10%) events • Suppression increases with increasing centrality R. Bailhache, Parallel, Tue 15:20

  36. Heavy flavour decay muons X. Lopez, Parallel, Tue 15:40 • Single muons at forward rapidity (-4<h<2.5) • punch-through hadrons rejected by requiring match with trigger chambers • Background from primary p/K decay not subtracted • estimated with HIJING to be 9% in the most central class (0-10%) for pT>6 GeV/c • RCP for inclusive muons in 6<pT<10 GeV/c • suppression increases with increasing centrality m

  37. Quarkonia dissociation in the medium J/y statistical recombination thermal dissociation LHC J. Castillo, Plenary, Mon 16:30

  38. J/y RAA at forward rapidity H. Yang, Parallel, Fri 15:20 • Inclusive J/y RAA • pp reference from pp data set at 2.76 TeV • Contribution from B feed-down not subtracted • J/y are suppressed with respect to pp collisions • J/y RAA almost independent of centrality

  39. J/y: comparison with RHIC H. Yang, Parallel, Fri 15:20 • Less suppression than at RHIC at forward rapidity: • RAA(ALICE) > RAA(PHENIX, 1.2<y<2.2) • Similar suppression as at RHIC at midrapidity • RAA(ALICE)≈ RAA(PHENIX, |y|<0.35) • Caveats: • Contribution from B feed-down not subtracted • Cold nuclear matter effects different at RHIC and LHC • Need for p-A collisions at LHC ALICE, LHC, forward rapidity PHENIX, RHIC, mid-rapidity PHENIX, RHIC, forward rapidity

  40. J/ RCP: ALICE vs ATLAS H. Yang, Parallel, Fri 15:20 • Less suppression in ALICE than in ATLAS • ALICE: • m+m - in 2.5<y<4.0 • e+e- in |y|<0.8 • pT>0 GeV/c • ATLAS: • |y|<2.5 • 80% of J/y have pT>6.5 GeV/c • error in the 40-80% bin not propagated

  41. Summary • In November 2010, heavy ion collisions entered a new era with the first of PbPb data sample at the LHC (√s=2.76 TeV) • Medium with 3 times higher energy density than at RHIC • Abundance of hard probes • Smooth evolution of global (bulk) event characteristics from RHIC to LHC energies • Precision measurements in the next future • Better constraints for existing models • Hard probes: novelties, surprises, challenges for theory • High pT hadrons • Strong suppression (factor 7 at pT~7 GeV/c) • Heavy quark RAA similar to that of pions at high pT • Quarkonia: • J/y less suppressed than at RHIC at forward rapidity • ALICE vs. ATLAS: hint for less suppresion at low pT, than at high pT

  42. J/ψ in pp 7 TeV D. Tapia Takaki, Fri 15:00 ... and more Multistrange baryons and resonances in pp 7 TeV A. Maire, Tue 16:50 D. Gangadharan, Tue 14:40 D mesons in pp 7 TeV G.M. Innocenti, Fri 16:30 Light and hyper nuclei A. Kalweit, Fri 18:10 R. Lea, Fri 15:50 Vector mesons in pp and PbPb C. Markert, Tue 17.30 L. Massacrier, Fri 14:40 Directed flow in PbPb G. Eyyubova, Fri 17:10

  43. Backup

  44. Detector status in PbPb 2010 run

  45. Energy density • From RHIC to LHC: • increase in dET/dh per participant pair by a factor 2.5 • Similar centrality dependence • Energy density of the medium from Bjorken formula • Where t = (unknown) formation time • ≈ 3×Bjt at RHIC

  46. Particle identification • PID in the central barrel • dE/dx in TPC • Up to 159 samples • Resolution ~ 5% • dE/dx in ITS • Low momentum reach • Time of Flight by TOF • 3s separation: • p/K up to 2.5 GeV/c • p/K up to 4.0 GeV/c

  47. p0 from conversions • p0gge+e-e+e- • Need precise knowledge of material budget • Tomography with photon conversions • Material budget (11.4% X0 up to middle radius of TPC) agrees within +3.4% -6% with its implementation in GEANT

  48. Identified hadron spectra

  49. Negative charged p, K, p spectra • Comparison with hydro predictions • OK for pions and kaons, disagreement for (anti)protons • Spectra harder than at RHIC energies • Protons flatter at low pT • Indicate stronger radial flow

  50. Positive charged p, K, p spectra • Spectra harder than at RHIC energies • Protons flatter at low pt • Comparison with hydro predictions • OK for pions and kaons, protons are off

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