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The ALICE experiment at LHC Martin Poghosyan For the ALICE Collaboration

pp (Nov. 2009). The ALICE experiment at LHC Martin Poghosyan For the ALICE Collaboration. SILAFAE 2010 Valparaíso, C hile Dec . 6 - 12, 2010. Pb-Pb (Nov. 2010). ~1000 members from ~30 countries. ~ 70 members from four Latin American Countries . PUEBLA, Autonomous Univ. of Puebla

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The ALICE experiment at LHC Martin Poghosyan For the ALICE Collaboration

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  1. pp (Nov. 2009) The ALICE experiment at LHC Martin Poghosyan For the ALICE Collaboration SILAFAE 2010 Valparaíso, Chile Dec. 6 - 12, 2010 Pb-Pb(Nov. 2010) M.Poghosyan

  2. ~1000 members from ~30 countries M.Poghosyan

  3. ~ 70 members from four Latin American Countries PUEBLA, Autonomous Univ. of Puebla CULIACAN, Universidad Autonoma de Sinaloa MEXICO D.F., Universidad NacionalAutonoma de Mexico; Inst. de Fisica MEXICO D.F., Universidad NacionalAutonoma de Mexico; Inst. de CienciasNucleares MEXICO D.F., Merida, Centro de Investigaciony de EstudiosAvanzados del IPN CINVESTAV HABANA, Centre de AplicacionesTecnologicasyDesarrollo Nuclear LIMA, Pontificia Universidad Catolica del Peru CAMPINAS, UniversidadeEstadual de Campinas UniCamp SAO PAULO, Universidade de Sao Paulo, Instituto de Fisica • Hardware • V0 (MB trigger) • ACORDE (CR trigger) • EMCAL • UPGRADES: VHMIPD, AD • www • Official web page • Indico • Software • Unfolding • Event Display • Analysis • Jets/ Event Structure • Cosmic Ray Physics • Diffractive Physics • Strangeness M.Poghosyan

  4. Detector configuration • A Large Ion Collider Experiment • High granularity (dN/dy~8000) • Minimized material • Good PlD • Good acceptance for pt down to 100 MeV/c ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%) TRD (7/18) EMCAL (4/12) PHOS (3/5) M.Poghosyan

  5. Detector configuration • A Large Ion Collider Experiment • High granularity (dN/dy~8000) • Minimized material • Good PlD • Good acceptance for pt down to 100 MeV/c ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%) TRD (7/18) EMCAL (4/12) PHOS (3/5) M.Poghosyan

  6. Charged particle multiplicity measurement with Silicon Pixel Detector • Two innermost layers of the ITS • Radii of 3.9/7.6 cm (|η| < 2.0/1.4) • ~8 M channels • Trigger & Tracking • ~80% active • Fast aligned/calibrated and used to estimate the Fiducial window = ΔθΔφ = 25mdar×80 mrad y x SPD2 SPD1 z • position of the interaction point • number of primary tracks ( |η| < 1.4; pT > 50 MeV/c) M.Poghosyan

  7. Multiplicity distribution K. Aamodt et al., EPJ C68 (2010) 345 M.Poghosyan

  8. How to go from Inel>0 to Inel, NSD ? • The Inel>0 sample is an accurate measurement but • One has to correct for diffractive processes for going from Inel>0 to Inel or NSD. • Mainly normalization problem: densities of particles in diff. processes are rather small • at mid-rapidity, but their cross-sections are not negligible. • What is the definition of diffraction? • Theory: coherence, quantum numbers, …. Pomeron exchange • Experiment: rapidity gap • How much do we really rely on gap measurements with "Swiss cheese” detectors? • no data at lower energies for comparison • useless for analytical models M.Poghosyan

  9. Inel. and NSD for ALICE at 0.9 and 2.36 TeV K. Aamodt et al., EPJ C68 (2010) 89 • Data samples are selected as follows: • SPD or V0A orV0C for Inel at 900 GeV(at least one charged particle in 8 units of pseudorapidity) • V0A andV0C for NSD at 900 GeV • At 2.36 TeV V0 was not in. • MC (efficiency/process-type/…): • PYTHIA and PHOJET • SD and NSD are mixed using SD and Inel cross-sections from UA5 and E710 • at 900 GeV 0.153 ± 0.023 (UA5) • at 1.8 TeV 0.159 ± 0.024 (E710) – practically no extrapolation needed for 2.36 TeV M.Poghosyan

  10. Measuring SD and DD with ALICE Strategy: Identify diffractive process based on the kinematics of produced particles in 9 units of pseudorapidity. ALICE Work in progress ALICE Work in progress ALICE Work in progress Understanding of diffraction dissociation of hadrons is important for understanding hh, hA and AA collisions. Diffractive intermediate states have a small influence on hA and AA total cross-section (at current energies they are close to a black limit) but they have a strong impact on hh interaction cross-section and on inclusive spectra in hh, hA and AA collisions. M.Poghosyan

  11. p-Nucleus absorption cross section Full tracking requires much more Alignment Proper material budget description Proper transport through detector M.Poghosyan PLC 20J. Schukraft 11

  12. Transverse momentum distribution at 900 GeV K. Aamodt et al., Phys. Lett. B693 (2010) 53 ITS+TPC tracking Spectrum seems to get harder towards mid-rapidity (jets become oriented in the tr. plane?) M.Poghosyan

  13. Inclusive spectra as a function of √s M.Poghosyan

  14. <pt> as a function of Nch Number of cut Pomerons ~ sΔ pt2 ~ Number of cut Pomerons Number of charged particles ~ Number of cut Pomerons M.Poghosyan

  15. Particle Identification No vertex cut ! M.Poghosyan PLC 20J. Schukraft

  16. Identified particle spectra M.Poghosyan

  17. V0 reconstruction M.Poghosyan

  18. Strangeness at 900 GeV M.Poghosyan

  19. Strangeness at 7 TeV W → L K X → L p S*→ L p K*→ K p M.Poghosyan

  20. Charm at 7 TeV J/Y → e+e- |y| < 1 J/Y → m+m-, y = 2.5 - 4 1 M.Poghosyan

  21. Antiproton/proton ratio at mid-rapidity K. Aamodt et al., PhysRevLett105 (2010) αP = 1.2, αω = 0.44; C ≈ 5 = ½ln s C = 5.7 ± 1.1 D = -0.15 ± 0.45 αOdd = 0.84 ± 0.36 If one requires D>0: D = 5*10-9 ± 3.8 M.Poghosyan

  22. Bose–Einstein correlations (HBT) K. Aamodt et al., Phys. Rev. D82 (2010) 052001 identical pions unlike-sign pions pair momentum multiplicity M.Poghosyan

  23. Source radius at √s = 900 GeV K. Aamodt et al., Phys. Rev. D82 (2010) 052001 Source radius vs Multiplicity Source radius vs Multiplicity • Radius increases with Nch, comparable to ISR, RHIC, Tevatron • rather constant vs <kT> • flat baseline results to kTdependent radius • dependence usually interpreted as sign of ‘flow’ in heavy ions Using different baselines M.Poghosyan

  24. Charged particle multiplicity density at mid-rapidity in central Pb-Pb collisions K. Aamodt et al., arXiv:1011.3916 dNch/dη ~ 1600 ± 76 (syst) at √sNN= 2760 GeV growth with √s stripper in AA than in pp Measured value is mainly on high side of expectations M.Poghosyan

  25. Multiplicity vs centrality in Pb-Pb at √sNN= 2760 GeV • submitted to arXive on 7 December M.Poghosyan

  26. Multiplicity vs centrality & models (after tuning) M.Poghosyan

  27. Comparison with the average from RHIC experiments (done by PHENIX) Factor: 2.1 Factor: 2.4 Factor: 4.1 What is the physics behind this? M.Poghosyan

  28. dN/dη depends on A4/3 or A1.1? A. Capella, A. Kaidalov, J. Tran Thanh Van, arXiv:hep-ph/9903244 (note, published before the RHIC era!) A4/3 - Gribov-Glauberwithout enhanced diagrams A1.1 - Gribov-Glauberwith enhanced diagrams M.Poghosyan

  29. dN/dη depends on A4/3 or A1.1? A. Capella, A. Kaidalov, J. Tran Thanh Van, arXiv:hep-ph/9903244 (note, published before the RHIC era!) A4/3 - Gribov-Glauberwithout enhanced diagrams A1.1 - Gribov-Glauberwith enhanced diagrams In fact, this dependence is a consequence of having large-mass diffractive intermediate states. Thermalisation and QGP formation strongly depend on the strength of the interactions between Pomerons. M.Poghosyan

  30. +30% RHIC ALICE v2 vs pt and centrality v2 as a function of pt K. Aamodt et al., arXiv:1011.3914 practically no change with energy v2 as a function of centrality 30% increase from RHIC for pt integrated v2 (because of increase of <pt>) M.Poghosyan

  31. Suppression of chargedparticle production at large pt K. Aamodt et al., arXiv:1012.1004 RAA = 1 for (very) hard QCD processes in absence of nuclear modifications M.Poghosyan

  32. Suppression of chargedparticle production at large pt K. Aamodt et al., arXiv:1012.1004 RAA = 1 for (very) hard QCD processes in absence of nuclear modifications Suppression of high pt particles ( ~ leading jet fragments) Minimum RAA ~ 1.5 – 2 x smaller than at RHIC Rising with pt ! (ambiguous at RHIC !) accuracy limited by pp reference M.Poghosyan

  33. Strangeness in Pb-Pb M.Poghosyan

  34. Charm in Pb-Pb M.Poghosyan

  35. Conclusions • ALICE is in a good shape • Performance of track and vertex reconstruction and particle identification close to design value for both pp and PbPb • Physics analysis well underway. Already some important results during one year of data taking: • Published results • pp • Nch multiplicity & distributions • 900 GeV: EPJ C65 (2010) 111 • 900GeV, 2.36 TeV: EPJ C68 (2010) 89 • 7TeV: EPJ C68 (2010) 345 • Momentumdistributions(900GeV) Phys. Lett. B693 (2010) 53 • Bose Einstein correlations (900GeV) Phys. Rev. D82 (2010) 052001 • pbar/p ratio (900GeV & 7TeV) PhysRevLett105 (2010) • Pb-Pb Multiplicity in central collisionsarXiv:1011.3916 • v2 arXiv:1011.3914 • RAA arXiv:1012.1004 • Multiplicity vscentralitysubmitted to arXive on 7 december Many ongoing analysis… M.PoghosyanEEEEEEEEEEEEEEEEEE€

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