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Status of B analysis via single electrons

Status of B analysis via single electrons. Andrea Dainese INFN – Legnaro based on work with: F.Antinori, C.Bombonati, M.Lunardon, R.Turrisi. Layout. Beauty measurement using displaced electrons Detection strategy Experimental issues: tracking and PID Results for pp and Pb-Pb

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Status of B analysis via single electrons

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  1. Status of B analysisvia single electrons Andrea Dainese INFN – Legnaro based on work with: F.Antinori, C.Bombonati, M.Lunardon, R.Turrisi ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  2. Layout • Beauty measurement using displaced electrons • Detection strategy • Experimental issues: tracking and PID • Results for pp and Pb-Pb • Physics Performance: • Sensitivity to pQCD predictions in pp • Beauty quenching • Conclusions / Outlook ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  3. rec. track e Primary Vertex B d0 X Measuring beauty via electrons • Expected yields of charm (b.r.: 10%) and beauty (b.r.: 11% +10% as bc e) decay electrons: • b quark has ct  500 mm decay electrons d0 ~ few-100 mm What’s the background? transverse plane ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  4. Background 1: charm decays • Heavy-quark decays: • b→B→e • b→B→D→e • c→D→e beauty pp charm(background) ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  5. Decays of light mesons and Dalitz decays (mostly p0) Photon conversions (g→e+e-) in the beam pipe and ITS innermost layer Charged pions mis-identified as electrons Background 2: other sources pp NO PID ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  6. rec. track e Primary Vertex B d0 X Detection strategy • Electron PID: reject most of the hadrons • Impact parameter cut: reduce charm and bkg electrons • Subtract (small) residual background ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  7. outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff. thanks to A.Andronic, S.Masciocchi Electron identification • Combined info from TRD (trans. rad.) and TPC (dE/dx) • TRD rejects 99% of the p and ALL heavier hadrons (pt > 1 GeV/c) outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff. • TPC further rejects residual pions (up to 99% at low p) • About 20% of electrons rejected fraction of misidentified pions ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  8. Cross section extraction procedure • In a given pt-bin, N “electrons” are counted, after PID and d0 cut: • N = Nb + Nc + Nbkg • Subtract the contribution from charm: Nb + Nbkg = N - Nc • estimated from D0 measurement (source of error) • Subtract the contribution from background: Nb = (N – Nc) - Nbkg • estimated from measured pions dN/dpt plus MC (source of error) • Correct for acceptance/efficiency: dNbcorr/dy = (Nb / e) • efficiency calculated with MC (source of error) • Multiply by the inelastic pp cross section (or by Pb-Pb overlap functions): dse from b/dy = spp.dNbcorr/dy • pp cross section measured at LHC (source of error) ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  9. Statistical: Systematic: Error from subtractions: Error from acc./effic. corrections: 10% (in principle pt-dependent) Error from cross section normalization: 5% for pp, 9% for Pb-Pb (pt-independent) dep. on d0 cut ~10% dep. on d0 cut pp Error contributions ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  10. Systematic error: prefers tight cut (high signal purity) dominates at low pt Statistical error: prefers loose cut (small d0 MIN) dominates only at high pt Optimization of d0 cut in bins of pt pp, 109 events “old TRD PID” ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  11. “new TRD PID” Statistics Summary 109 pp events 107 central (0-5%) Pb-Pb events “old TRD PID” “old TRD PID” ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  12. “old TRD PID” Errors Summary “old TRD PID” 109 pp events 107 central (0-5%) Pb-Pb events ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  13. pp: Sensitivity vs. pQCD From electrons in 2 < pt < 20 GeV/c, B mesons in 2 < ptmin < 30 GeV/c “old TRD PID” 109 pp events ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  14. Beauty Energy Loss : RAA “old TRD PID” 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  15. Heavy-to-light ratios: RB/D “old TRD PID” 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  16. First-year scenario • Only few TRD supermodules for 2008 pp run • What can we do with TPC(&TOF) PID only? • Optimization of dE/dx cuts for electrons ID p=4 GeV/c 40% TOF 0.1% Ne=Np=Nm=NK=Np C.Bombonati ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  17. First year: Statistical error TPC+TRD TPC C.Bombonati ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  18. Outlook • One year at nominal luminosity: • pp 1-18 GeV/c ➔ comparison with pQCD calc. • Pb-Pb 1-18 GeV/c ➔ RAA & v2 of beauty • First year pp: • up to 14 GeV/c (with larger errors) using ITS+TPC+TOF • Next steps: • preparation of Analysis task for ESD/AOD • analysis of PDC events • preparation of procedure for background subtraction (charm, misid. pions) and for corrections (cuts, PID) ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  19. EXTRA SLIDES ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  20. LHC running conditions pp nominal run Pb-PB nominal run Ldt dt = 3.1030 cm-2 s-1 x 107 s 5.1037 cm-2 for pp run, 14 TeV Npp collisions = 2 .1012 collisions Ldt = 5.1026 cm-2 s-1 x 106 s 5.1032 cm-2 PbPb run, 5.5 TeV NPbPb collisions = 2 .109 collisions   Muon triggers: ~ 100% efficiency, < 1kHz Muon triggers: ~ 100% efficiency, ~ 1kHz Electron triggers: ~ 50% efficiency of TRD L1 20 physics events per event Electron triggers: Bandwidth limitation NPbPb central = 2 .108 collisions Hadron triggers: Npp minb = 2 .109 collisions Hadron triggers: NPbPb central = 2 .107 collisions   ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  21. Model Comparisons(HERA-LHC Workshop) CERN/LHCC 2005-014 hep-ph/0601164 Compare predictions by several different models charm beauty Good agreement between collinear-factorization-based calculations: FO NLO and FONLL kT factorization (CASCADE) higher at large pT ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  22. Energy extrapolation via pQCD? • Different systems (pp, p-Pb, Pb-Pb) will have different s values • Results in pp at 14 TeV will have to extrapolated to 5.5 TeV (Pb-Pb energy) to compute, e.g., nuclear modification factors RAA • pQCD: “there ratio of results at 14 TeV/5.5 TeV has ‘small’ uncertainty” beauty charm 12% 8% MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  23. Cuts Summary ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  24. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background The charm contribution to the total electron spectrum is evaluated using the MC by introducing the charmed hadron pT distributions deduced from the D0K-+ measurement. - Charmed hadrons (Hc=D0,D+,D+s,+c) cross section assumed to be proportional to the D0 one. The Hc/D0 ratio is assumed to be 1.70  0.07 (*) Errors propagated from Hc to e level: - Monte Carlo corrections for the D0 measurement ~ 10% - Statistical error on the D0 pTdistribution - NN normalization not considered at this level (same as beauty) - The 69% uncertainty of D0 from b should become negligible after the beauty direct measurement (*) deduced by comparing the PYTHIA value with the ALEPH measured value [D.Abbaneo et al., Eur. Phys. J. C16 (2000) 597] ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  25. Cross section of electrons from B inner bars: stat. errors outer bars: stat.  pt-dep. syst. errors not shown: norm. error (5% pp, 9% Pb-Pb) 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  26. Problem: depends on B cross section shape used in simulation systematic error. How large? Extraction of a minimum-pt-differential cross section for B mesons Using UA1 MC method (*), also adopted by ALICE m (thanks to R.Guernane for useful discussions) The B meson cross section per unit of rapidity at midrapidity for ptB > ptmin is obtained from a scaling of the electron-level cross section measured within a given electron parameters space e The semi-electronic B.R. is included here We use , where pT are the previously used bins,  = [-0.9, 0.9] and d0 = [d0 MIN, +] m (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121 ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

  27. F ~ 1 % Extraction of a minimum-pt-differential cross section for B mesons Robusteness of the procedure For pte > 2 GeV/c,can find an “optimal” ptmin, for which the additional systematic error is negligible ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

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