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Open Heavy Flavour reconstruction in ALICE: D 0  K p and B  e +X

ALICE-Italia, Cagliari, 4-5 Maggio 2005. Open Heavy Flavour reconstruction in ALICE: D 0  K p and B  e +X. Andrea Dainese per il gruppo ALICE Padova F.Antinori, A.D., J.Faivre, M.Lunardon, R.Turrisi. Contents. Physics motivations Heavy-quark production at the LHC c and b energy loss

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Open Heavy Flavour reconstruction in ALICE: D 0  K p and B  e +X

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  1. ALICE-Italia, Cagliari, 4-5 Maggio 2005 Open Heavy Flavour reconstruction in ALICE:D0  Kpand B  e +X Andrea Dainese per il gruppo ALICE Padova F.Antinori, A.D., J.Faivre, M.Lunardon, R.Turrisi ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  2. Contents • Physics motivations • Heavy-quark production at the LHC • c and b energy loss • ALICE cross sections baseline • Exclusive reconstruction of D0 Kp decays in pp and Pb-Pb collisions in ALICE • Inclusive beauty via single electrons • Future developments ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  3. HVQs production in pp at 14 TeV • Important test of pQCD in a new energy domain • remember the “15-years saga of b production at the Tevatron”*… • …and c production not yet fully reconciled • NLO predictions for LHC: uncertainties of factor > 2--3 CDF, hep-ex/0307080 FONLL: Cacciari, Nason Cacciari, Frixione, Mangano, Nason and Ridolfi, hep-ph/0312132 beauty charm HERA-LHC Workshop Proceedings using: Mangano, Nason, Ridolfi, NPB 373 (1992) * M.Mangano ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  4. increasing s sc(DGLAP+non-linear) sc(DGLAP) charm beauty Cartoon HQs as a probe of small-x gluon dynamics • Probe unexplored small-x region with HQs at low pT and/or forward y • down to x~10-4 with charm already at y=0 • Window on the rich phenomenology of high-density PDFs • gluon saturation / recombination effects • non-linear terms in PDFs evolution • Possible effect: enhancement of charm production at low pT w.r.t. to standard DGLAP-based predictions Eskola, Kolhinen, Vogt, PLB 582 (2004) Gotsmann, Levin, Maor, Naftali, hep-ph/0504040 ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  5. path length L hard parton Final-state effects in nucleus-nucleus: Parton Energy Loss • Partons travel ~ 4 fm in the high colour-density medium • Energy loss by gluon radiation (BDMPS) Casimir coupling factor: 4/3 for quarks 3 for gluons Medium transport coefficient gluon density and momenta Probe the medium R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  6. Q Lower E loss for heavy quarks? • In vacuum, gluon radiation suppressed at q < mQ/EQ  “dead cone” effect • Dead cone implies lower energy loss(Dokshitzer-Kharzeev, 2001) • Detailed calculation confirms this qualitative feature, although effect is small and uncertainties significant (Armesto-Salgado-Wiedemann, 2003) Exploit abundant massive probes at LHC & study the effect by measuring the nuclear modification factor for D and B Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [hep-ph/0106202]. N.Armesto, C.A.Salgado and U.A.Wiedemann, Phys. Rev. D69 (2004) 114003 [hep-ph/0312106]. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  7. Latest from RHIC: Charm Suppressed! RAA light-flvred hadrons electrons from c (b) decay pT (GeV) Effect of charm mass is small similar suppression as for light-flvred hadrons Calculations: Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  8. mass effect Color-charge and mass dep. of E loss with heavy-to-light ratios at LHC Heavy-to-light ratios: Compare g  h , c  D and b  B For 10 < pT < 20 GeV, charm behaves like a m=0 quark, light-flv hadrons come mainly from gluons RD/h enhancement probes color-charge dep. of E loss RB/h enhancement probes mass dep. of E loss Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  9. D0 K-p+ reconstruction • Exclusive channel direct measurement of the pt distribution ideal tool to study RAA • Weak decay with mean proper length ct = 124 mm • Large combinatorial background (dNch/dy=6000 in central Pb-Pb!) • STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices • Measurement of Impact Parameters (ITS+TPC) • Measurement of Momenta (ITS+TPC) • Particle identification (TOF) to tag the two decay products ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  10. rf: 50 mm < 60 mm for pt > 1 GeV/c z: 425 mm PIXEL CELL Two layers: r = 4 cm r = 7 cm Impact parameter resolution • Mainly provided by the 2 layers of silicon pixels in the ITS  9.8 M Systematic study of track impact parameter resolution: A.D. and R.Turrisi, ALICE-INT-2003-028. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  11. D0 K-p+: Selection of D0 candidates increase S/B by factor ~103! ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  12. D0 K-p+: Results Note: with dNch/dy = 3000, S/B larger by  4 and significance larger by  2 ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  13. 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 % ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  14. Sensitivity to NLO pQCD params pp s = 14 TeV ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  15. ‘High’ pt (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Low pt (< 6–7 GeV/c) Nuclear shadowing Pb-Pb pp Charm Quenching Dainese, EPJC33 (2004) 495. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  16. Beauty via single electrons in central Pb-Pb collisions • Main sources of background: •  misidentified as e • charm-decay electrons • Dalitz decays • photon conversions • strangeness decays • Detection strategy: • electron ID in TPC+TRD • impact parameter cut (B c ~ 500 m) • pt cut (large b mass  hard spectrum) ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  17. Electron Identification in TPC and TRD Background from charged pions suppressed by factor ~10-4 Example: e ID in TPC ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  18. Purity and statistics Signal-to-total ratio and expected statistics in 107 central Pb-Pb events 80% purity 8  104 e from B pt > 2 GeV/c , 200 < |d0| < 600 m ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  19. Statistical error on electrons from B • Statistical errors for 107 0-5% central Pb-Pb events • 200 < |d0| < 600 m electrons ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  20. Systematic errors • Error on MC corrections for tracking, selection, ID efficiencies • Error on subtraction of charm electrons (curr.tly from D0 measure) • Error on normalization to cross section per NN collision Error on e from charm (propagated from D0 meas.) ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  21. Cross section of electrons from B inner bars: stat. errors outer bars: stat.  pt-dep. syst. errors not shown: 11% normalization error ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  22. Extraction of a ptmin-differential cross section for B mesons Using electrons in 2 < pt < 20 GeV/c obtain B meson 2 < ptmin < 30 GeV/c inner bars: stat. errors outer bars: stat.  pt-dep. syst. errors not shown: 11% normalization error Note: quenching curves for illustration; Pb-Pb vs. pp comparison needed to study E loss E Loss Calculation: Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027. ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  23. Future developments: D0 Kp • Optimization of selection strategy • Maximize signal selection efficiency & minimize background contamination • Not trivial,especiallly at low pt, where background is large • Use guidance from (semi-)automatized methods for pattern recognition • We started from Linear Discriminant Analysis (LDA) • our new postdoc, J.Faivre, did LDA for X and W at STAR (next slide) • Strategy: use LDA as a guide for optimization of ‘classical cuts’, under better ‘human’ control ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  24. Variable 2 Variable 1 Best axis b b a a Variable 1 Variable 1 Linear Discriminant Analysis (LDA) Classical cuts: either high efficiency or low contamination BKG BKG SGN SGN The idea of LDA: cut on best linear combintion of the variables Example: W in STAR classical LDA ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  25. e Future developments: beauty • In progress: internal note and PPR contribution on “Beauty via single electrons in Pb-Pb” • Next step: dedicated study for pp collisions • Physics performance goals: • sensitivity on measurement of b cross section (vs ATLAS/CMS, vs QCD calculations) • combined with Pb-Pb, sensitivity on high-pt suppression of B, and comparison with light-flavoured hadrons and D mesons • Study pp-specific issues: • define displaced electron track in pp scenario with ‘broad beams’ • use global event topology for better b selection? ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

  26. Summary • Study for D0 reconstruction in Pb-Pb and pp (p-Pb in Trieste byR.Grosso) carried out • strong simulation requirements: fast simulation partially employed • many (most) critical items addressed: PID, primary vertex in pp, feed-down from beauty … • results are very promising • analysis code skeleton prepared (in $ALICE_ROOT/ANALYSIS/) • starting second iteration, using LDA to optimize selection strategy • Performance for beauty production measurement in Pb-Pb assessed, in terms of pt coverage and expected errors • fast simulation partially employed • 2 < B ptmin < 30 GeV/c, similar coverage with single m(Guernane et al.) • starting study for pp • Main studies for “Charm and Beauty” PPR section http://alice.web.cern.ch/Alice/ppr/chap6_6dir/current/alice_chap6_6.ps ALICE Italia - Cagliari, 04.05.2005 Andrea Dainese

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