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ALICE Experiment

ALICE Experiment. Roman Lietava University of Birmingham. Physics motivation Detectors Observables and Physics Performance Summary. ALICE Collaboration. 937 members (63% from CERN MS) 77 Institutions, 29 Countries. ALICE UK: 6 members University of Birmingham. Collision Systems.

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ALICE Experiment

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  1. ALICE Experiment Roman Lietava University of Birmingham • Physics motivation • Detectors • Observables and Physics Performance • Summary UK HEP Forum

  2. ALICE Collaboration 937 members (63% from CERN MS) 77 Institutions, 29 Countries ALICE UK: 6 members University of Birmingham UK HEP Forum

  3. Collision Systems Year √sNN (TeV) L0 (cm-2s-1) Run time (s/year) 14.0 1031 107 April 2007 2007/2008 5.5 1027 106 • Other collision systems and energies: • pA, lighter ions (Sn, Kr, Ar, O) • pp @ 5.5 TeV UK HEP Forum

  4. Physics Motivation The study of Quantum Chromodynamics: • A-A collisions: - physics of many particles interacting strongly, QCD phase transition • p-p and p-A collisions: - benchmark for AA collisions - specific aspects • Ultra peripheral AA collisions –  physics • Cosmic ray physics UK HEP Forum

  5. QCD Phase Diagram Nonperturbative phenomena  hep-ph/020516 Lattice QCD PLB478(2000)447 UK HEP Forum

  6. Space Time Evolution of the Collisions UK HEP Forum

  7. ALICE Physics Goals • Large acceptance • Good tracking capabilities • Selective triggering • Excellent granularity • Wide momentum coverage • P.I.D. of hadrons and leptons • Good sec. vertex reconstr. • Photon Detection Use a variety of experimental techniques! • Degrees of freedom as a function of Thadron ratios and spectra, dilepton continuum, direct photons • Global observables: Multiplicities,  distributions • Early state manifestation of collective effects:elliptic flow • Energy loss of partons in quark gluon plasma: jet quenching, high pt spectra, open charm and open beauty • Deconfinement:charmonium and bottomonium spectroscopy • Chiral symmetry restoration: neutral to charged ratios, res. decays • Fluctuation phenomena - critical behaviour:event-by-event particle comp. and spectra • Geometry of the emitting source:HBT, impact parameter via zero-degree energy flow • pp collisions in a new energy domain UK HEP Forum

  8. Alice Detector • Tracking (B=0.2-0.5 T): - Inner Tracking System (ITS) – pixels,drift,strips - Time Projection Chamber (TPC) - Transition Radiation Detector (TRD) • PID: - TPC - TRD - Time Of Flight (TOF) - High Momentum PID (HMPID) • Muons: dimuon arm • Calorimetry: - PHOton Spectrometer (PHOS) - Electromagnetic Calorimeter (EMCAL) - under discussion UK HEP Forum

  9. Bat 40 ATLAS CMS ALICE UK HEP Forum From R.J.Cashmore,IOP Bham

  10. ALICE Detector Acceptance Muon arm: 2.4<h<4 PMD 2.3<h<3.5 FMD: -5.4<h<-1.6, 1.6<h<3 UK HEP Forum

  11. PTResolution UK HEP Forum

  12. ALICE PID p/K TPC+ITS (dE/dx) K/p e /p p/K e /p TOF K/p p/K HMPID (RICH) K/p 0 1 2 3 4 5 p (GeV/c) TRD e /p PHOS g /p0 1 10 100 p(GeV/c) • p, K, p identified in large acceptance (2p * 1.8 units h) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/c • Electrons identified from 100 MeV/c to 100 GeV/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD • In small acceptance HMPID extends PID to ~5 GeV • Photons measured with high resolution in PHOS, counting in PMD, and in EMC UK HEP Forum

  13. ALICE Trigger (Birmingham) • ALICE trigger features: • Global trigger selection • Past-Future protection • Different trigger rates for group of detectors • Dynamic suppression of common triggers Triggering on: • collision centrality • high pT muons • high pT electrons • jets • Rates and pile-up: • Pb-Pb collisions: 8 kHz interaction rate L=1027 cm-2 s-1 • 60 % pile-up probability • p-p collisions: 200 kHz interaction rate L=3x1030 cm-2 s-1 • 100 % pile-up probability • TPC drift time 90 s UK HEP Forum

  14. First ALICE trigger board (LTU) UK HEP Forum

  15. Medium characteristics Particle multiplicities Particle spectra Particle ratios Flow Particle correlation Fluctuations Hard probes Jets Heavy quark and quarkonium production Direct photons and dileptons Observables UK HEP Forum

  16. Multiplicity What multiplicity do we expect? dNch/dh ~ 2500 We can extrapolate from RHIC data: ALICE design: dN/dy=8000 (from K.Kajantie, K.Eskola) UK HEP Forum

  17. Transverse mass spectra NA57 NA57 Pb-Pb at s=17GeV Transverse mass spectra  Freeze out temperature Transverse flow 5% most central events UK HEP Forum

  18. Hadron Ratios Degree of chemical equlibrium: Constraint on timescales of flavour production mechanism

  19. One year of ALICE running (107 events)  Ls up to pt = 12 GeV/c Topological signature, not reliant on identification of daughters L Detection % % of rec. Ls vs pt S/B  1 5.5 L/event pt (GeV/c) Entries L Yield Reconstructed pt spectrum M(pp) (GeV/c2) UK HEP Forum pt (GeV/c)

  20. Hard Processes Modified by the Medium • Jet quenching: • energy degradation of leading hadrons, pt dependence; • modification of genuine jet observables; • energy imbalance in dijet events • Open charm/beauty production • c’onium & b’onium bound states production Final state (medium) interaction versus initial state (Cronin,shadowing) interaction  p-p and p-A measurement are mandatory UK HEP Forum

  21. High pt particles suppressed in Au-Au relative to pp, d-Au. High pT Suppression • RAB = d2N/dpTdh TABd2spp/dpTdh AA coll STAR results: pp coll Number of coll d-Au, Cronin effect Au-Au, jet quenching J. Adams et al., Phys. Rev. Lett. 91, 072304 (2003). UK HEP Forum

  22. Di-jets Mini-jets in Au+Au at RHIC (STAR) In central Au-Au events,although trigger jet is clearly visible, “away-side” jet is not visible, as predicted from strong absorption in a high colour charge density volume, e.g. that produced in a QGP Missing jet UK HEP Forum

  23. Jets Reconstruction in ALICE • Jets are produced copiously. • Jets are distinguishable from the HI underlying event. pt (GeV) 20 100 200 2 100/event 1/event 100K/year + HI event 100 GeV jet UK HEP Forum

  24. Heavy Quarks • Initially produced quarks experience the full collision history: • Short time scale for production: t1/mQ • Production suppressed at larger times: mQ»T • Long time scale for decay tdecay»tQGP • The large masses of c and b quarks make them qualitatively different probes ( massless partons) Observables: • Total production rate • transverse momentum distribution • correlation between quark and antiquark UK HEP Forum

  25. Heavy QuarksD0K-p+ reconstruction in ALICE cuts depend on D0pt D0 K-p+ ct = 123.7  0.8 mm BR: (3.83  0.09) % Affected by main vertex resolution in p+p case UK HEP Forum

  26. Heavy QuarksD0K-p+ reconstruction in ALICE PbPb: pT>1 GeV/c pp: pT>0 GeV/c UK HEP Forum

  27. Heavy QuarkoniaJ/Y and  via Dielectrons J/Y: Mass resolution for : 100 MeV (B = 0.4T) : Acceptance down to pt = 0 GeV/c ! UK HEP Forum

  28. Motivation for pp Study • First insight in pp collisions in new energy domain (s  14 TeV), study of evolution of soft hadronic physics • Contribution to knowledge of underlying minimum bias (background) pp events to complement other LHC physics programmes (Higgs search, Bphysics, etc.) • Provide pp data as a reference for study of other collision systems (p-A, A-A) • Low multiplicity data to commission and calibrate various components of ALICE UK HEP Forum

  29. ALICE Features for pp • Excellent particle identification(TOF andHMPID) • ptcut-off • Magnetic field (but this could be lowered) • Material thickness (hard to change) • ATLASand CMShave better -coverage UK HEP Forum

  30. Summary Permanent closure of L3 door in RB26 (05/03/04) • ALICE experiment is getting ready: • - the detectors are being built • the software is getting ready • the understanding • of the physics • potential grows … ... and so does the number of people involved UK HEP Forum

  31. ALICE Setup HMPID TRD TPC MUON SPEC. PMD ITS TOF PHOS FMD UK HEP Forum

  32. Decay channel K* K+p- Invariant mass distribution for 550 events Low pt Physics ExamplesResonances: K* Au+Au minimum bias pT 0.2 GeV/c |y|  0.5 Statistical error only Entries STAR Preliminary • STAR data shows clear K* on background • Other resonances (r,w,f0... ) are being extracted UK HEP Forum

  33. Single event Raw correlation function Uncorrected for Coulomb R = 8 fm, l = 0.5 Tracking with ITS+TPC, B = 0.2T HBTEvent-by-Event p+p+ HBT C(Qinv) Qinv (GeV) d6N d3N d3N C(p1,p2)= d3p1 d3p2 d3p1d3p2 Resolution for B=0.2T UK HEP Forum

  34. Number of Participants Participants Npart Spectators pA: Npart=n+1 AA: UK HEP Forum

  35. UK HEP Forum

  36. Charged Particle Multiplicity 200 GeV AuAu 130 GeV AuAu dN/d 0-6%cent Ntot = 4100 ±210 Ntot = 4960 ±250 25-35%cent 45-55%cent UK HEP Forum 

  37. g-jet with PHOS+EMCAL + TPC Proposed EMCAL |h|<0.7 Df ~ 120o jet TPC Collision axis 8% 2% h g PHOS+EMCAL EMCAL => trigger and g-jet, + improve resolution on Ejet UK HEP Forum

  38. Elliptic flow STAR Preliminary scaled with n(quarks) dN(pT,b,y,)=A(1 + 2v1(pT,b,y) cos() + 2v2(pT,b,y)cos(2  ) +…)  - the angle relative to reaction plane • v1=0 at y=0 by symmetry • v2 – information about the information about the equation of state UK HEP Forum

  39. Why is elliptic flow interesting? y x py px Raimond Snellings coordinate space • Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric) • Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp) • Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow Momentum space UK HEP Forum

  40. Elliptic flow as a function of centrality Non-flow considerable for central and peripheral events UK HEP Forum STAR Nucl. Phys. A698 (2002) 193

  41. 1+2 Experiments 0 1 2 10 100 pt (GeV/c) Qs T=LQCD Hard processes Modified by the medium Bulk properties ALICE PID CMS&ATLAS UK HEP Forum

  42. RAA clearly different between mesons and baryons Importance of PID at high pt p+p baseline measurement! High ptRHIC Results UK HEP Forum

  43. Heavy QuarksOpen Charm via Hadronic Decays Pb+Pb: pt > 1 GeV/c Significance dN/dpt p+p: pt > 0 GeV/c ! Significance = Significance dN/dpt UK HEP Forum

  44. Input to simulation cc: PYTHIA, tuned to NLO calculations, with CTEQ4L and nuclear shadowing EKS98 Background: HIJING Reconstruction effects included PID with TOF Heavy QuarksOpen Charm via Hadronic Decays System (s) Pb-Pb (5.5TeV) pp (14TeV) Signal for107(109)evts 13000 20000 S/B 11 % 50 % Significance for107(109)evts 37 84 Pb+Pb sminv = 12 MeV (B = 0.4T) PbPb:pT>1 GeV;pp: pT>0 UK HEP Forum

  45. - Reduction of single inclusive high pt particles Parton specific (stronger for gluons than quarks) Flavour specific (stronger for light quarks) Measure identified hadrons (p, K, p, L, etc.) + partons (charm, beauty) at high pt Suppression of mini-jets same-side / away-side correlations Change of fragmentation function for hard jets (pt >> 10 GeV/c) Transverse and longitudinal fragmentation function of jets Jet broadening  reduction of jet energy, dijets, g-jet pairs Parton Energy Loss - p+p and p+A measurements crucial UK HEP Forum

  46. Parton Energy Loss UK HEP Forum

  47. UK HEP Forum

  48. UK HEP Forum

  49. Permanent closure of L3 door in RB26 (05/03/04) UK HEP Forum

  50. c/b Quarkonia dN/dh=8000 105 J/ dN/dh=5000 Y Y 103 J/ Events/100 MeV Events/25 MeV 104 104 102 5 10 15 0 9 11 2 3 4 10 Mm+m-(GeV) via dimuons • 1 month statistics of PbPb √sNN=5.5 TeV; |h| < 2.4 2.5<h < 4 UK HEP Forum

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