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Hard (& Heavy) QCD probes in heavy-ion collisions at the LHC: ALICE performance

5.5 TeV. 208 Pb. 208 Pb. LHC. Hard (& Heavy) QCD probes in heavy-ion collisions at the LHC: ALICE performance. Andrea Dainese, University of Padova for the ALICE Collaboration. Go for deep deconfinement at LHC. Next step in the “quest for QGP” …

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Hard (& Heavy) QCD probes in heavy-ion collisions at the LHC: ALICE performance

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  1. 5.5 TeV • 208Pb • 208Pb • LHC Hard (& Heavy) QCD probes in heavy-ion collisions at the LHC:ALICE performance Andrea Dainese,University of Padova for the ALICE Collaboration XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  2. Go for deep deconfinement at LHC Next step in the “quest for QGP” … • LHC: factor 30 jump in w.r.t. RHIC much larger initial temperature study of hotter, bigger,longer-living ‘drops’ of QGP •  closer to ‘ideal’ QGP • easier comp. with theory (lattice) ‘Deep de-confinement’ XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  3. c Pb Q Pb c Hard Processes in AA at the LHC • Main novelty of the LHC: large hard cross section • Hard processes are extremely useful tools • large virtuality Qhappen at t = 0 small “formation time”Dt ~ 1/Q (for charm: Dt < 1/2mc ~ 0.1 fm/c << tQGP ~ 5–10 fm/c) • Initial yields and pt distributions in AA can be predicted using pp measurements + pQCD + collision geometry + “known” nuclear effects • Deviations from such predictions are due to the medium medium formed in the collision time XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  4. QGP @ LHC cold matter Parton Energy Loss • Due to medium-induced gluon emission • Average energy loss (BDMPS model): path length L QCD process: emitted gluon itself radiates  EL2 hard parton Casimir coupling factor: 4/3 for quarks 3 for gluons Medium transport coefficient gluon density and momenta R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291. C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) 014008 [arXiv:hep-ph/0302184]. XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  5. D mesons quenching reduced Ratio D/hadrons (or D/p0) enhanced and sensitive to medium properties Lower Loss for Heavy Quarks? • Heavy quarks with momenta < 20–30 GeV/cv << c • In vaccum, gluons radiation suppressed at Q < mQ/EQ “dead cone” effect • Dead cone implies lower energy loss(Dokshitzer-Kharzeev, 2001) • Recent detailed calculation confirms this qualitative feature (Armesto-Salgado-Wiedemann, 2003) see talk by N.Armesto Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202]. N.Armesto, C.A.Salgado and U.A.Wiedemann [arXiv:hep-ph/0312106]. XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  6. Experimental study of energy loss • Compare pt distributions of leading particles in pp and nucleus-nucleus collisions (+ p-nucleus as a control) Nuclear modification factor: Important step forward at the LHC: Compare quenching of massless and massive probes • Study jets (or ‘jets’): • ‘jets’ - (charged) particle correlations (RHIC tells us they can tell a lot!) • jets - with calorimetry (CMS/ATLAS speciality see talk by C.Roland) see talk by D. d’Enterria XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  7. The ALICE Detector |h| < 0.9 TPC + silicon tracker g,e, p, K, p identification 2.5 < h < 4 muons XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  8. Exclusive charm in ALICE: D0 K-p+ • Exclusive reconstruction direct measurement of the pt distribution ideal tool to study RAA • Large combinatorial background (dNch/dy=6000 in central Pb-Pb!) • Main selection: displaced-vertex selection • pair of tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex Invariant mass analysis to “count” D0 XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  9. Results. Example: Pb-Pb pt-integrated (K,) Invariant Massdistribution (pt –integrated) (corresponding to 107 central Pb-Pb events ~1 monthrun) Statistical Significance of the Signal: after background subtraction analysis for Pb-Pb and pp done in bins of pt and main errors estimated Details on selection strategy in: N.Carrer, A.D. and R.Turrisi, J. Phys. G29 (2003) 575. A.D. PhD thesis (2003) [arXiv:nucl-ex/0311004] XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  10. Low pt (< 6–7 GeV/c) Nuclear shadowing ‘High’ pt (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Sensitivity on RAA for D0 mesons XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  11. Energy-loss simulation • Energy loss simulated using BDMPS quenching weights by Salgado and Wiedemann • Plus: • realistic path lengths of partons in the medium • dead-cone correction for heavy quarks • transport coefficient for central Pb-Pb collisions at LHC estimated requiring hadrons RAA ~ 0.2–0.3 (~ RHIC) C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) 014008 [arXiv:hep-ph/0302184]. XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  12. QGP @ LHC cold matter Average relative energy loss XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  13. RAA ~ 0.4–0.5 increasing at high pt RAA ~ 0.7–0.8 decreasing at high pt RAA with Quenching A.D. Eur. Phys. J. C, in press [arXiv:nucl-ex/0312005]. XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  14. D/h ratio: RD/h = RAAD / RAAh RD/h ~ 2–3 in hot QGP sensitive to medium density D/hadrons ratio (1) • Expected enhancement because of lower charm quenching • Experimentally use double ratio: RAAD/RAAh • many systematic errors of both Pb-Pb and pp cancel out! XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  15. S/(S+B) S per 107 Pb-Pb events pt > 2 GeV/c, d0 > 180 mm: 50,000 electrons with S/(S+B) = 90 % Open Beauty in electron channel • Inclusive B  e + X: • electron ID + cut on its pt & on its impact parameter XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  16. # Jets in |h|<0.5 with Et > Etmin per central Pb-Pb event Jet Rates at the LHC 1/event 104/month (year) use High Level Trigger XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  17. Jet Quenching Studies (1) • High-pt suppression: RAA up to ~ 40–50 GeV/c in 1 year • Azimuthal correlation studies • What about “identified jets”? Quite unclear … • Energy plays a minor role as jet observable • Small effect of quenching on the energy inside a given cone (Salgado and Wiedemann (2003)) r(R): Energy contained in a cone of size R normalized to the energy contained in a cone of size 1. XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  18. Jet Quenching Studies (2) • Simple MC quenching model (which reproduces results of Salgado and Wiedemann) Most interesting signals from the radiated energy are at high R and low pt Very challenging due to the large background from the underlying event Good tracking in the region pt < 1–2 GeV/c is needed XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

  19. Summary • LHC: study properties for deconfined QCD matter via hard probes and their quenching • ALICE: good potential in the hard probes sector • Outstanding example: ALICE can exclusively reconstruct D0 mesons in Pb-Pb collisions with dNch/dy = 6000! • measure charm production in 0 < pt < 15 GeV/c (at least) • study the mass and flavour dependence of QCD energy loss • And more: • beauty detection via semi-electronic decays • jet studies with charged tracks XXXIXth Rencontres de Moriond - QCD, March 28 - April 4, 2004 Andrea Dainese

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