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ALICE Physics Performance

ALICE Physics Performance. Andrea Dainese (University and INFN – Padova) for the ALICE Collaboration. Specific case: Open Charm. Contents. Physics of QCD matter at high-temperature/-density in AA at LHC. Physics performance. Observables: soft physics hard probes. ALICE set-up and

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ALICE Physics Performance

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  1. ALICEPhysics Performance Andrea Dainese (University and INFN – Padova) for the ALICE Collaboration CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  2. Specific case: Open Charm Contents Physics of QCD matter at high-temperature/-density in AA at LHC Physics performance • Observables: • soft physics • hard probes ALICE set-up and detector performance CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  3. Central collisions SPS RHIC LHC study of: s1/2(GeV) 17 200 5500 dNch/dy 430 700 2- 8 x103 hotter e (GeV/fm3) 2.5 3.5 15- 40  5 -10 bigger Vf(fm3) 103 7x103 2x104 Lattice QCD, mB=0  3 longer-lived tQGP (fm/c) < 1 1.5- 4.0 4-10 “fire-balls” of QCD matter “Deep de-confinement”  closer to “ideal” QGP  easier cmp with theory Heavy-ion Physics at LHC • LHC: factor 30 jump in w.r.t. RHIC CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  4. Novel aspects of HI Physics at LHC • High-density parton distributions • bulk of partons at x < 10-3 • saturated gluon densities (?) • strong gluon shadowing • Hard processes • significant part of cross section • can be calculate by pQCD • happen at initial state • probe the matter they traverse charm 12 w.r.t. RHIC 100 CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  5. What multiplicity do we expect? • Old estimates: dNch/dy ~ 2000 – 8000 • ALICE designed for 8000 • RHIC extrapolations (?) dNch/dy ~ 2500 (from K.Kajantie, K.Eskola) CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  6. (Hard) ? ? ? more J/ ? Jets Open charm, beauty c cbar Jets c Open charm, beauty D0 Observables Measure all observables in Pb-Pb, pp, pPb to disentangle cold and hot nuclear-medium effects CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  7. L3 Magnet B < 0.5 T: 0.2 T low pt acceptance, 0.5 T pt resolution at high pt HMPID RICH @ high pt EMCAL US Proposal for EM calorimeter in barrel acceptance PID TOF PID  next talk by T. Awes TRD Electron ID PMD g multiplicity FMD Forward multiplicity TPC Tracking, dEdx ZDC Centrality ITS Low pt tracking Vertexing MUON m-pairs PHOS g,p0 PIXELS + FMD -5.1 <  < 3.4 Measurement of dNch/dy ALICE Detector The dedicated HI experiment at LHC Designed to measure most observables CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  8. f K+K- K* resonance in Pb-Pb ALICE Physics List (1) • Global observables • multiplicities, rapidity distributions • Degrees of freedom as a function of T • hadrons ratios and spectra, dilepton continuum, direct photons • Early state manifestation of collective effects • elliptic flow • Chiral symmetry restoration • neutral to charged ratios, resonance decays • Fluctuation phenomena • event-by-event particle composition, spectra • Measure the geometry of the emitting source • HBT CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  9. ALICE Physics List (2) • Study deconfinement • quarkonia • Heavy-flavour production • open charm and open beauty • Energy loss of partons in the quark-gluon plasma • jet quenching, high-pt spectra, open charm and open beauty • pp, pA for comparison: • measure PDF and shadowing • pp, pA specifics: • global pp properties • diffractive events CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  10. Measurement of charm productionin Pb-Pb and pp via D0 Kp Physics motivation Present exp. picture Sensitivity to ds(D0)/pt and s(D0) Detection strategy for D0 exclusive decays Selection and results Experimental issues: ALICE performance CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  11. Charm enhancement in Pb-Pb at SPS? NA50: enhancement of dimuons in intermediate mass region Explained if assume a charm enhancement by 3.5 over simple scaling with Ncoll NA50 @ SPS sNN = 17 GeV PHENIX @ RHIC sNN = 130 GeV First results from RHIC PHENIX: single-electron spectrum consistent with semi-electronic decays of D mesons (after subtraction of other e sources) Well reproduced by Pythia  Ncoll Seems to exclude such a large enhancement Charm: present experimental picture CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  12. w > 0 w > 0.5 GeV energy loss Heavy/Light for L = 5 fm in hot medium Essential to measure: • total cc production cross-section • pt distribution of charm particles In order to probe: • energy loss of c quarks • additional cc production Charm: what do we expect at LHC ? (see talk by D. Kharzeev later) • Thermal charm production: • maximum predicted T ~ 800-1000 MeV not much lower than charm mass • some models predict additional production comparable to initial “hard” yield precise measure of cross sections in pp, (pA), AA • Energy loss: • fast partons loose energy (mainly) by gluon radiation study energy loss of charm quarks (RAA = “AA/pp(pA) vs pt”) • “dead cone” effect suppresses energy loss in heavy quarks w.r.t. light quarks study D/p vs pt in AA (pA) and in pp CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  13. Charm: D0 Kp strategy • Weak decay with mean proper length ct = 124 mm • Impact Parameter (distance of closest approach of a track to the primary vertex) of the decay products d0 ~ 100 mm • STRATEGY: invariant mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices • Measurement of Impact Parameters • Measurement of Momenta • Particle identification to tag the two decay products CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  14. Time Projection Chamber Track finding & Measurement of Momenta Magnetic field (B = 0.4 Tesla in this study) 1 % at low pt < 2% up to 10 GeV/c Tracking efficiency Central Pb-Pb ~12,000 tracks in the barrel … … here D0 Kp is a challenge TPC TPC TOF TPC+ITS TPC+ITS < 60 mm for pt > 1 GeV/c Pb-Pb, dNch/dy=6000 ITS Inner Tracking System Track finding, Measurement of the Momenta & Measurement of Impact Parameters Time Of Flight Particle Identification (K/p separation) PIXELS Charm: Detection strategy with ALICE CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  15. Charm: signal and background • Signal: • charm cross section from NLO pQCD (MNR program), average of results given by MRST and CTEQ5M PDFs (with EKS98 in Pb-Pb) • signal generated using PYTHIA, tuned to reproduce pt distr. given by NLO pQCD • Background: • Pb-Pb: HIJING (dNch/dy=6000) [20k evts];pp: PYTHIA [8M evts] • What is the background to hadronic D decays? combinatorial background given by pairs of uncorrelated tracks with large impact parameter CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  16. d0K d0 <<0 cos pointing 1 Charm: Selection of D0 candidates • Main selection: Displaced vertex selection • pair of tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  17. pp Pb-Pb 0.5<pT<1 GeV/c Significance = 11 2<pT<2.5 GeV/c significance = 21 pt > 1 GeV/c pt > 0 ! 12<pT<14 GeV/c significance = 11 Charm: Results Note: in pp, large uncertainty on primary vertex position: beams de-focused to reduce luminosity to 1030 cm-2s-1 CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  18. Charm: estimate of errors • Statistical error on the selected signal = 1/Significance • Main systematic errors considered: • correction for feed-down from beauty (B.R. B  D0 is 65%!): error of ~8% assuming present uncertainty (~80%) on @ LHC • Monte Carlo corrections: ~10% • B.R. D0 Kp: 2.4% • extrapolation from N(D0)/event to ds(D0)/dy: • pp: error on (~5%, will be measured by TOTEM) • Pb-Pb: error on centrality selection (~8%) + error on TAB (~10%) CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  19. ds(D0)/dy for |y| < 1 and pt > 1 GeV/c (65% of pt > 0) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 % ds(D0)/dy for |y| < 1 and pt > 0.5 GeV/c (91% of pt > 0) statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 % sinel = 5 % Charm: d2s(D0)/dptdy and ds(D0)/dy CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  20. pp Pb-Pb Charm: B D “a` la CDF” • Impact parameter of D0 can be used to separate primary and secondary D0 • Background shape from side-bands in inv. mass • Background subtracted CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  21. test beam: p id. as e = 1 % p as e < 10% up to 5 GeV/c Open Beauty in electron channel Electron identification in TRD-TPC (pt > 1 GeV/c) + impact parameter in ITS CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  22. beauty charm misid. p S/(S+B) S per 107 Pb-Pb events pt > 2 GeV/c, d0 > 180 mm: 80,000 electrons with S/(S+B) = 90 % Open Beauty in electron channel • B electron identification: • cut on pt : reject low-pt backgrounds (conversions, dalitz of light mesons) • cut on impact parameter: reject background from D mesons CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  23. Quarkonia: electrons • Acceptance for J/ () (w/o and w/ 3 GeV/c cut on e pT = effect of TRD L1 trigger) J/ acceptance down to pt = 0!  expected mass resolution for  @ B = 0.4T: 100 MeV CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  24. Impact parameter with pixels J/ impact parameter (mm) Secondary J/ from B decay • B  J/ e+e- (B.R.: 1%) • Large contribution to observable J/ signal • Has to be disentangled to study J/ suppression/enhancement • Use impact parameter of reconstructed J/ CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  25. Parton energy loss • Effects of medium-induced gluon radiation: • reduction of high-pt particles (observed at RHIC) • suppression of mini-jets (same-side / away-side correlations) • change of fragmentation functions • Need to measure: • identified particles at high pt • particle correlations and jet structure • heavy-quark jets } Comparison pp, pA, AA “traditional” jet-measures  calorimetry talk by T. Awes quenching studies with charged tracks CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  26. pt(seed) = 5 GeV/c pt > 2 GeV/c 1 < R < 2 1/R dN/dR R < 0.3 R away side jet signal pt (GeV/c) Quenching studies with tracks • First studies (HIJING events – generator level, no det.) • Leading-particle correlations • Two-particle correlations CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  27. g p0 S/B  1 5.5 L/event Entries L Yield Reconstructed pt spectrum M(pp) (GeV/c2) High pt • Estimates of upper limit for 1 year ALICE run: • 107 central events Pb-Pb ~103 tracks with pt > 50 GeV/c • 109 min. bias events pp ~103 tracks with pt > 40 GeV/c • Identified particles: • D0 up to 15 GeV/c, B ~ 10 GeV/c (under study) • L up to 12 GeV/c • g/ p0 separation up to 100 GeV/c with PHOS CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  28. Summary Comprehensive study of matter produced in AA at LHC measure many observables ALICE detector provides good performance for most of them Examples from the “hard-probes sector”: D0 charm cross section down to 1 GeV/c in Pb-Pb handle on b cross section? beauty detection via electronic decays identified particles at high-pt (L, g, p0)+“jets w/o calorimetry” CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  29. Back-up Slides CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  30. pt resolution pp VS Pb-Pb B = 0.4 T CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  31. Primary vertex in pp (1) • Track reconstruction in TPC+ITS • track seeding uses the position of the primary vertex: • (x, y) from beam position (resolution ~ 150 mm) • z from pixels information (resolution ~ 150 mm) • Vertex reconstruction in 2 steps: • VERTEX FINDING: using DCA for track pairs • VERTEX FITTING: (inspired by CMS and ATLAS methods) • give optimal estimate of the position of the vertex • give vertex covariance matrix • give a c2 CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  32. Primary vertex in pp (2) • Inspiration: ATLAS TRT TDR • Criterion used to reject mismeasured and secondary tracks from the fit: cut on the maximum contribution to the c2 ci2 < c2max • if c2max is too low too many tracks are rejected and we loose resolution • if c2max is too high bad or secondary tracks enter the fit and we loose resolution • This cut is tuned, as a function of event multiplicity, in order to optimize the resolution CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  33. Primary vertex in pp (3) CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  34. tag: PION tag: KAON tag: PROTON others, tag: non-id PID in TOF • How is PID used for hadronic charm? • identification of pions allows to reject (p,p) pairs from combinatorial background • identification of kaons allows to have a cleaner sample (candidates with 1 track tagged as a K) in the low pT region • TOF gives an estimate of a particle mass: Pb-Pb 6000 pp CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  35. Tagging probabilities Pb-Pb Loss of signal due to K tagged as p: Pb-Pb 10 % pp 2 % pp CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  36. Background spectra CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  37. PYTHIA TUNING CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  38. pT < 1 GeV/c 1 < pT < 2 GeV/c 2 < pT < 3 GeV/c 3 < pT < 5 GeV/c pT > 10 GeV/c 5 < pT < 10 GeV/c Charm event in pp-PYTHIA • Charged particles in ||<0.9 and pT > 200 MeV/c CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  39. Correlation plot CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  40. Tuning of cuts • Cuts are tuned as a function of pt in order to maximize the significance of the signal CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  41. The history of signal … Total D0 / event 141 decaying in Kp 5.4 with K and p in acc. 0.5 after track rec. 0.14 after (p,p) rejection 0.13 after selection cuts 0.0013 … and of background Selection cuts reduce background by a factor ~10-7 10-2 Signal history in Pb-Pb CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  42. What if multiplicity is lower? • We used dNch/dy = 6000, which is a pessimistic estimate • Recent analyses of RHIC results seem to suggest as a more realistic value dNch/dy = 3000 (or less) • Charm production cross section: • estimate from NLO pQCD (only primary production, no collective effects) • average of theoretical uncertainties (choice of: mc, mF, mR, PDF) • BKG proportional to (dNch/dy)2 • We can scale the results to the case of dNch/dy = 3000: S/B = 44 % SGNC = 74 (this only from scaling, obviously better with retuning of cuts) CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  43. Errors VS pt Pb-Pb pp CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  44. B - Final electron sample CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  45. Muons: Quarkonia (I) • Acceptance for J/ () (w/o and w/ 1 (2) GeV/c cut on m pT) J/Y  CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

  46. Muons: Quarkonia (II) • Mass resolutions: from MUON TDR • Significances (MUON TDR): CMS Heavy-Ion Workshop in Delphi - June 8, 2003 Andrea Dainese

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