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Semileptonic BR of b hadrons and charm counting at LEP

Semileptonic BR of b hadrons and charm counting at LEP. 5th International Conference on Hyperons, Charm and Beauty Hadrons, Vancouver David Waller, Carleton University Ottawa, Canada. Outline. Introduction to BR sl and n c Latest LEP BR sl result (ALEPH)

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Semileptonic BR of b hadrons and charm counting at LEP

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  1. Semileptonic BRof b hadrons and charm counting at LEP 5th International Conference on Hyperons, Charm and Beauty Hadrons, Vancouver David Waller, Carleton University Ottawa, Canada

  2. Outline • Introduction to BRsl and nc • Latest LEP BRsl result (ALEPH) • Latest LEP nc result (DELPHI) • Compare Z0 and Upsilon(4S) results, and experiment to theory • Conclusions and outlook David Waller, Carleton University BEACH 2002, Vancouver

  3. Precise calculations and measurements of BRsl possible. Experimental results for BRsl at low end of theoretical expectations BRsl if hadronic  hadronicrelated to nc. Introduction to BRsl and nc nc = average # of c and c per b decay measure BR0c and BR2c David Waller, Carleton University BEACH 2002, Vancouver

  4. Latest BRsl measurement from LEP (ALEPH) • 2 separate analyses  results combined • analysis A: uses lepton momentum transverse to jet axis ( pT) • analysis B: uses correlation between charge of lepton and estimated b flavour of hemisphere. • P sample: high pT lepton (pT > 1.25 GeV/c) in opposite hemisphere estimates flavour of b.. • J sample: 2 hemisphere charge estimators (similar to “jet charge”) from opposite hemisphere combined (QH ) to estimate flavour of b. • Electron and Muon ID: TPC pad pulse height used to help estimate dE/dx (previously only TPC wire info used). Efficiency , especially for lower pT electrons (+30%). • TPC pad and wire dE/dx information combined. David Waller, Carleton University BEACH 2002, Vancouver

  5. BR(b  lX): pT Analysis (using B sample) Likelihood fit used to determine fractions of b l and b  c  l in data. BR(b  lX) and BR(b  c lX) determined from fractions and detection efficiencies. David Waller, Carleton University BEACH 2002, Vancouver

  6. BR(b  lX): pT Results BR(b  lX)=0.1107  0.0007stat  0.0013syst  0.0044model BR(b c lX)=0.0752  0.0010stat  0.0044syst  0.0035model • Lepton pT modelling dominates uncertainty (“model” uncertainty). • Fractions of D, D*, D1, and D2* in final state (and 3- and 4-body decays) varied. • ACCMM, ISGW, ISGW * * models not used. • Uncertainty in lepton pTspectrum dominated by proportions of final states, not models used for each final state. Statistical correlation = -0.45 David Waller, Carleton University BEACH 2002, Vancouver

  7. BR(b  lX): Charge Correlation Analysis exclude exclude Sample P: high pT lepton b flavour/charge estimator,Qlepton pTlepton . Sample J: “hemisphere charge” b flavour/charge estimator. • Likelihood fit used to determine fractions (in each sample) of leptons with charge opposite to charge estimator of other hemisphere. David Waller, Carleton University BEACH 2002, Vancouver

  8. BR(b  lX): Charge Correlation Result BR(b  lX) =0.1057  0.0011stat  0.0029syst  0.0020model BR(b c lX) =0.0752  0.0010stat  0.0044syst +0.0012model -0.0016model • Less sensitive to b  lXkinematics modelling. • Uncertainty from b  W c  l rate dominates (produces same sign lepton as b  l). Statistical correlation = -0.76 pT & Q Corr. Combined: BR(b  lX) =0.1070  0.0010stat  0.0023syst  0.0026model Eur. Phys. J. C 22 (2002) 613. David Waller, Carleton University BEACH 2002, Vancouver

  9. BR(b  lX): Other LEP Results • LEPEWWG fit (2001) of heavy flavour measurements at the Z gives • Level of sophistication has increased over years (7 years since LEP 1!) and uncertainties have decreased. BR(b  lX)=0.1056 0.0011 0.0018 and LEP BR(b  lX)PDG 2000=0.1073 0.0018 David Waller, Carleton University BEACH 2002, Vancouver

  10. Latest ncanalysis from LEP (DELPHI) • Measures wrong sign (WS) charm production in b decays. • WS D hadrons (e.g. b D+ X) produced almost exclusively in b  DDX decays (input for nc) . • D+, D0, and Ds+ are exclusively reconstructed. preliminary David Waller, Carleton University BEACH 2002, Vancouver

  11. Latest ncanalysis from LEP (DELPHI) • pD determined in b centre-of-mass frame. • Flavour of c quark in D(s) determined by charge of K(). • Flavour of b quark at decay time estimated using ANN (0 to 1) combining: • weighted track charges of opposite hemisphere. • weighted track charges of same hemisphere (excluding D tracks). • Y(D)= ANN (D) or 1-ANN (D) preliminary David Waller, Carleton University BEACH 2002, Vancouver

  12. Latest ncanalysis from LEP (DELPHI) • For Ds+, binned likelihood fit of Y(D) distribution determines numbers of WS and RS Ds+ . • For D0 and D+ need pD also to determine numbers of WS and RS D (2-d fit). • WS D0 and D+ suppressed compared to WS Ds+ . preliminary David Waller, Carleton University BEACH 2002, Vancouver

  13. Latest ncresult from LEP (DELPHI, preliminary) • Combine measured NWS and NRS D hadrons, BR(b  D,DX) from previously combined results (PDG), and acceptance correction (WS / RS) to get WS BR’s. BR(b  D0X) + BR(b  D-X)= (9.3  1.7stat  1.3syst  0.4BR(DK()))% BR(b  Ds-X) = (10.1  1.0stat  0.6syst  2.8BR(Ds- KK) )% David Waller, Carleton University BEACH 2002, Vancouver

  14. Comparisons • Z0 and CLEO results are consistent for ncand BR(b  lX). • Experimental results are consistent with theory but suggest low  (renormalization scale). This means NNLO calculations should be done (only NLO right now). • Further improvements to nc will help pin down mc. 2001 David Waller, Carleton University BEACH 2002, Vancouver

  15. Conclusions and Outlook • Many LEP analyses have measured ncand BR(b  lX). • Only latest ones presented here. • Could not do justice to all in short time (apologies)! • LEP data consistent with CLEO data and theory (Neubert, et al.) but maybe NNLO calculations needed to be safe (?). • See theory BR(b  lX) talks later this week... • DELPHI wrong sign charmresult to be finalized. • New OPAL nc result nearing completion (Fall 2002). To come... David Waller, Carleton University BEACH 2002, Vancouver

  16. ALEPH lepton energy spectrum David Waller, Carleton University BEACH 2002, Vancouver

  17. Other ncresults from LEP • Previous LEP nc results obtained using: • exclusive reconstruction of D+, D0, Ds+ and c-baryons, “classic” charm counting (OPAL,DELPHI,ALEPH) • inclusive measurement using decay topology to separate 0c, 1c and 2c b decays (DELPHI) • exclusive reconstruction of D and D in b decays to (partially) determine BR(b  DDX) (ALEPH) David Waller, Carleton University BEACH 2002, Vancouver

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