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Charm and beauty with ALICE at LHC

Charm and beauty with ALICE at LHC. Rosario Turrisi University and INFN, Padova, Italy for the ALICE Collaboration. Contents. Heavy flavors and heavy ions Key performances of ALICE Charm cross section and p t sensitivity Beauty cross section Conclusions and Perspectives.

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Charm and beauty with ALICE at LHC

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  1. Charm and beauty with ALICE at LHC Rosario Turrisi University and INFN, Padova, Italy for the ALICE Collaboration

  2. Contents • Heavy flavors and heavy ions • Key performances of ALICE • Charm cross section and pt sensitivity • Beauty cross section • Conclusions and Perspectives

  3. not covered here PbPb @ =5.5 TeV Heavy flavors and heavy-ions Why measure heavy flavors at LHC ? • Interest in its own right: discovery potential! More specific to our issue (hot and dense matter): • quarkonium suppression: deconfinement signature • probes of the medium: • early formation (initial parton-parton), most energetic phase • thermal (late) production ? • energy loss (medium dependent?) • B J/ important background for direct J/  • open heavy flavors as natural normalization for QQ studies open flavors channels K e c D  K b B  eX  pp reactions, pQCD, nuclear effects (geometry, shadowing) INPUT OUTPUT medium properties

  4. g c path length L RAA measured at RHIC with pions: clear high-pt suppression Quark energy loss: basics • Common explanation: parton energy loss due to gluon radiation • Average energy loss (BDMPS model): CR Casimir factor = 3 for gluons 4/3 for quarks q = medium transport coefficient  gluon density and momenta • Study to get the medium effect A.Dainese, C.Loizides and G.Paic, hep-ph/0406201 RAA =1 if AA is superposition of independent pp collisions Quark Matter Conference ’04 R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, Nucl. Phys. B483 (1997) 291. C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) 014008 [arXiv:hep-ph/0302184].

  5. Energy loss with heavy flavors ? • Effect present in light mesons, what about other particles? • D,B meson originate from c,b quarks Cr = 4/3, whereas light flavors originate mainly from gluons (C=3) • Dead cone effect*: due to destructive interference, gluons radiation is suppressed at angles  < mQ/EQ • Comparison among -D-B in order!  extrapolation from q=15 GeV2/fm at RHIC… a worst case (q=100 GeV2/fm)! charm q = 100 GeV2/fm at LHC1 beauty *Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202]. 1. K.J.Eskola, K.Kajantie, P.V.Ruuskanen and K.Tuominen, Nucl. Phys. B570 (2000) 379 [hep-ph/9909456].

  6. Cross sections • NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDF’s, EKS98 in Pb-Pb for shadowing (shadowing = modification of PDF’s, reduction of cross section) Taking into account F,R a factor 4 arises between min. and max. cross section… Mesons multiplicities central collisions In acceptance! ~0.5 D0  K ~0.2 B  eX

  7. pt resolution: σ= 1(2)% @ 1(10) GeV 9% @ 100 GeV EFFICIENCY pions kaons Tracking performance impact parameter resolution:  σ= @ pt=1.3 GeV < 50 μm   < 150 μmz

  8. test beam: p id. as e = 1 % PID: e,, K, p PbPb events, dN/dy=6000 Combined π/e ~ 10-4 @ pt~1-2 GeV electrons TPC p (GeV/c) TRD TOF hadrons

  9. Selection cuts • D0  K • decay topology • impact parameter of tracks (in bending plane, d0~100 μm) • momenta • identification ~ 0.5 D0 with |y|<1 but also 12000 charged /K in PbPb collisions cos(pointing angle) vs. impact parameters product

  10. Performance: D0K • K, MINV integrated over pt • 107 PbPb events (one-month run) • dN/dy(y=0) = 6000 (charged) measurement of pt distribution

  11. Current estimation of q = 100 GeV2/fm mc=0 mc=1.2 GeV/c2 Charm energy loss in ALICE N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation

  12. b e+X: strategy • Task: tag ~ 0.8 e /event from b decays among ~ 103 electrons from other sources • Main backgrounds: • pions misidentified as electrons • Dalitz decays • charm semi-electronic decays • photon conversions in the detector materials • strange decays • Strategy: • high impact parameter: c ~ 500 μm for beauty • high momenta: beauty harder than lighter flavors • electron/pion separation critical

  13. pt and d0 spectra beauty electrons charm electrons charged pions

  14. background cure charm electrons pt thr. light mesons electrons d0 thr. charged pions identification pT> 3 GeV pT> 2 GeV pT> 1 GeV b e+X: purity and statistics pT>2 GeV, 180  d0 600 mm • 90% purity • 50,000 B's (including TRD efficiency)

  15. pT> 3 GeV pT> 2 GeV pT> 1 GeV Conclusions & perspectives • ALICE has a good potential to measure heavy flavors in different channels • Charm: • production cross section • pt distribution • study of energy loss • Beauty: • Production cross section • Coming up • reconstruction of b decay topologies • b’s pt distribution, energy loss study • additional D, D* channels • semi-electronic charm (beauty background!) • … 11% S/B, significance=37

  16. BACKUPS

  17. 2 * 1.8 units of pseudo-rapidity rf: 50 mm 9.8 Mch z: 425 mm PIXEL CELL Two layers: r = 4 – 7 cm Solenoid magnet B<0.5 T • TRD- 6 layers for: • electron/pion separation at pt>1 GeV • factor 100 rejection at 2 GeV • tracking complement, mass resolution • 100 MeV/c2 @  • high pt trigger (onia studies) ALICE detectors ITS- 6 Layers, 3 technologies Material budget < 1% of X0 per layer! Silicon Pixels vertices resolution in xy (0.2 m2, 9.8 Mchannels) Silicon Drift resolution in z (1.3 m2, 133 kchannels) Double-sided Strip connection w/TPC (4.9 m2, 2.6 Mchannels) { TPC 88 m3 , 510 cm length, 250 cm radius Ar (90%) + CO2 (10%) 88 μs drift time main tracking device, dE/dx TOF - Multigap Resistive Plate Chambers  < 100 ps pions, kaons, protons separation (see later) electrons/pions at low pt

  18. TPC + ITS projection of the full  range (front view) 60 <  < 62 Total charged multiplicity dNCH/dy (y=0) Current baseline: 6000 Tested up to: 8000

  19. Quarkonia detection • see Andres Sandoval’s talk (I hope…)

  20. Signal & background pt

  21. Centrality

  22.  tuning or beam offset LHC run parameters Pile-up in TPC + and ion-density limit Fall 2007 2008 *Lmax(ALICE) = 1031 ** Lint(ALICE) ~ 0.7 nb-1/year • and, later, more systems: pA, light ions (Sn, Kr, Ar,O) & other energies (pp @ 5.5 TeV).

  23. x regime

  24. pQCD extrapolations • NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDFs (EKS98 in Pb-Pb for shadowing) Taking into account F,R a factor 4 arises between min and max x-section… inclusive cross section already a valuable information!

  25. Hadron multiplicities pp PbPb ~140 D0/D0 ~5 D0  K ~8 B or b ~0.85 B  eX

  26. SPD multiplicity -2<<2 Acceptance

  27. b->e+X: contamination

  28. Particle identification 2  ||<0.9 Various techniques… … in a wide momentum range

  29. Charm detection performance

  30. Expected multiplicity/running conditions • ALICE optimized for dN/dy(y=0) =4000-6000, tested extensively up to 8000 • Extrapolating from RHIC… 5 15.0 10.0 Nch/(0.5Npart) dNch/dh|h<1 103 5.0 5 dNch/dh ~ 1300 dNch/dh ~ 2500 1.0 2 10 102 103 102 103 104 √s (GeV) hep-ph0104010

  31. inner bars: statistical outer bars: systematic ds(D0)/dy for |y| < 1 and pt > 0 statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 % sinel = 5 % D0 K-p+:d2s(D0)/dptdy and ds(D0)/dy ds(D0)/dy for |y| < 1 and pt > 1 GeV/c (65% of s(pt > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 %

  32. Signal history, errors for PbPb Selection effectiveness… 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 Background reduced by a factor ~10-7 10-2

  33. q = 4 GeV2/fm at LHC requiring same hadron suppression as at RHIC Energy loss vs. dead cone Quantitative difference heavy/light mesons measurement? D/h ratio: RD/h = RAAD / RAAh Egluons/quarks fragmentation ~ 1/2 E gluons/quarks energy loss ~ 2 dead cone makes the difference! RD/h ~ 2 in hot QGP sensitive to medium density

  34. LHC PbPb @ = 5.5 TeV General motivation • ALarge Ion Collider Experiment is the LHC experiment dedicated to the study of the Quark Gluon Plasma… QGP  a (locally) thermally equilibrated state of matter in which color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. “Partons are deconfined” high energy & large volume hadronic matter strong interaction QGP

  35. Performance studies • Detector description with the state-of-the-(ALICE)-art code AliRoot • Charm/beauty signal tuned to NLO pQCD pt spectrum (custom tuning of PYTHIA) • Background from HIJING, 6000 charged particles per unit rapidity at midrapidity Priorities: • the exclusive decay of the D0  K (golden channel): • test bench for secondary vertex detection, pid • very high background • inclusive b  eX decay • secondary vertices • electron identification • “easy” measurement of cross section

  36. QGP evidences and probes • SPS experiments got some evidence that matter may behave in odd ways (not just as “typical” hadrons) • RHIC exps show confirmation of the new behaviour,mostly with light mesons and hadrons • Possible improvements: • experimental smoking gun of QGP? (see f.e. T. Hallman talk at ICHEP 2004, Beijing, China) • study of QGP properties? • At LHC (Pb-Pb @ 5.5 ATeV): • morestrictlyμB=0 • higher energy density larger volume DEEP DECONFINEMENT? longer lifetime • Hard cross section dominant • Could heavy flavors represent a good tool at LHC?

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