Determination of | V cb | Using Moments of Inclusive B Decay Spectra

1. Determination of |Vcb| Using Moments of Inclusive B Decay Spectra BEACH04 Conference June 28-July 3, 2004 Chicago, IL Alex Smith University of Minnesota • Introduction • Hadron Mass Moments in BXcln • Lepton Energy Moments in BXcln • Photon Energy Moments in BXsg decays • Combined Fit to Determine |Vcb| and HQET parameters • Summary Alex Smith – University of Minnesota

2. Measuring |Vcb| • |Vcb| is a fundamental parameter of the Standard Model • Inclusive semileptonic bc transitions provide a good laboratory in which to measure |Vcb| • Exclusive semileptonic modes suffer large theoretical uncertainties • Purely hadronic final states too complicated • Weak bcln process still obscured by strong interactions • Strong interactions of inclusive semileptonic decays described by • Perturbative QCD • Short-distance effects • Heavy Quark Effective Theory/Operator Product Expansion • Non-perturbative long-distance effects Alex Smith – University of Minnesota

3. Heavy Quark Effective Theory • Semileptonic rate expressed as a double expansion in as and 1/mb • Use “kinetic mass” formulation of Uraltsev, et al(hep-ph/0401063) Alex Smith – University of Minnesota

4. Moments of Observable Spectra • Moment of distribution defined in usual way: • A commom set of HQET parameters appear in expressions for • Lepton energy moments in BXcln • Hadronic mass-squared moments in BXcln • q2 moments in BXcln • Photon energy moments in BXsg • Semileptonic width • Simultaneously fit these measurements to determine HQET parameters eg., lepton energy moment: Alex Smith – University of Minnesota

5. The CLEO II Detector • CESR symmetric e+e- collider • Energy near U(4S) • Most relevant features of detector: • Hermeticity of detector neutrino reconstruction • Excellent shower resolution of CsI calorimeter photons, electrons • Good charged particle resolution and dE/dx of drift chamber leptons Alex Smith – University of Minnesota

6. l El qWl X W MX En q n B Hadronic Mass and q2 Moments in BXcln • Neutrino reconstruction technique Identify lepton 1 hep-ex/0403052 Infer hadronic mass 3 Reconstruct neutrino 2 Alex Smith – University of Minnesota

7. l El qWl X W MX En q n B Hadronic Mass and q2 Moments in BXcln • Neutrino reconstruction technique Identify lepton 1 Infer hadronic mass 3 Reconstruct neutrino 2 Alex Smith – University of Minnesota

8. Hadronic Mass and q2 Moments in BXcln • Selection criteria applied to suppress continuum and enhance neutrino reconstruction • Fit differential decay rate in three dimensions: • q2 • MX2 • cosqWl • Fit Components and models: • BDlnHQET+measured FF’s • BD*ln HQET+measured FF’s • BD**ln ISGW2 • B(Xc)non-resln Goity-Roberts • BXuln ISGW2+NR • Secondary leptons CLEO MC • Continuum and fakes data Fit Components Note: histograms normalized to same area Alex Smith – University of Minnesota

9. Hadronic Mass and q2 Moments in BXcln • Fit projections • Fit provides reasonable description of the data • Branching fractions of individual modes are very model-dependent • Inclusive differential decay rate much less model-dependent q2 MX2 cosqWl |pl| En Alex Smith – University of Minnesota

10. Hadronic Mass and q2 Moments in BXcln • Results are consistent with previous CLEO measurements • Uncertainties and results comparable to BaBar measurements • q2 moments expected to be somewhat complementary to MX moments • Only measured by CLEO hep-ex/0403052 Alex Smith – University of Minnesota

11. Lepton Energy Moments in BXcln • Di-lepton event sample • Use one lepton as the “tag”: • pl > 1.4 GeV/c, e or m • ~97% of sample is primaryBXln • Lepton charge tags flavor of parent B meson • Look for signal electron in “tagged” events • pe > 0.6 GeV/c • Correct for backgrounds and efficiencies • Use charge and kinematic correlations to separate the spectra from primary and secondary leptons • Primary leptons are the signal hep-ex/0403053 Monte Carlo simulation of electron daughters from B decay Alex Smith – University of Minnesota

12. Lepton Energy Moments in BXcln Unmixed B0 Mixed B0 Primary Events Opposite B Secondaries Same B Secondaries Alex Smith – University of Minnesota

13. Lepton Energy Moments in BXcln Unmixed B0 Mixed B0 Primary Events Opposite B Secondaries Same B Secondaries Easily vetoed with kinematic cut 66% efficient X25 rejection Alex Smith – University of Minnesota

14. Subtract backgrounds Correct for efficiencies Algebraically solve for primary spectrum Lepton Energy Moments in BXcln Alex Smith – University of Minnesota

15. Lepton Energy Moments in BXcln • Correct for • EW radiation • B boost • Results consistent with previous CLEO measurements • Systematics-limited--- Uncertainty on moments comparable to BaBar • Integrate measured spectrum hep-ex/0403053 Alex Smith – University of Minnesota

16. Photon Energy Moments in BXsg • Large photon background from continuum processes • p0 and h veto • Suppress using neural network • Several different inputs related to event shape • Pseudo-reconstruction • Ks0 or K+/- • 1-4 pions, at most one p0 • Large subtraction necessary hep-ex/0108032 Alex Smith – University of Minnesota

17. Photon Energy Moments in BXsg • bsg measurement is key to extracting HQET parameters • Sensitive to mb • Mean energy (1st moment) roughly equal to mb/2 • Independent of mc • New analysis in progress • Previous analysis optimized for branching fraction measurement • New analysis of old data optimized for extraction of spectrum • New results soon Alex Smith – University of Minnesota

18. Measurements included in fit: 1st and 2nd photon energy moments : Eg > 2.0 GeV 1st and 2nd lepton energy moments : Ee > 0.7, 1.2, 1.5 GeV 1st and 2nd hadronic mass moments : Ee > 1.0, 1.5 GeV 1stq2 moment : Ee > 1.0, 1.5 GeV Chi-squared fit including full correlation matrix of measurements Uses O(1/m3) formulation and code from Uraltsev and Gambino (hep-ph/0401063) Includes perturbative corrections to account for lepton/photon energy cuts Will also use approach of Bauer, Ligeti, et al before finalizing results (hep-ph/0210027) Combined Fit to Determine |Vcb| Alex Smith – University of Minnesota

19. Combined Fit to Determine |Vcb| CLEO data (GeV2) Preliminary (GeV/c2) Alex Smith – University of Minnesota

20. Combined Fit to Determine |Vcb| CLEO data (GeV2) Preliminary 1st and 2nd Lepton Energy Moments (GeV/c2) Alex Smith – University of Minnesota

21. Combined Fit to Determine |Vcb| CLEO data (GeV2) Preliminary 1st and 2nd Photon Energy Moments (GeV/c2) Alex Smith – University of Minnesota

22. Combined Fit to Determine |Vcb| CLEO data (GeV2) Preliminary 1st and 2nd Hadronic Mass Moments (GeV/c2) Alex Smith – University of Minnesota

23. Combined Fit to Determine |Vcb| CLEO data (GeV2) Preliminary 1stq2 Moments (GeV/c2) Alex Smith – University of Minnesota

24. Only CLEO has measured photon energy, q2, hadronic mass, and lepton energy in a single experiment A solution consistent with all measurements is found Without BXsg,mb and mc almost completely correlated in fit Most of the sensitivity to mb comes from BXsg measurement First moment  mean photon energy  mb/2 (approx.) Other measurements primarily constrain mb-Cmc, C~0.6 q2 moment gives some complementary information Nearly independent of mp2 Combined Fit to Determine |Vcb| Alex Smith – University of Minnesota

25. Combined Fit to Determine |Vcb| CLEO data (GeV/c2) Preliminary (GeV/c2) Alex Smith – University of Minnesota

26. Combined Fit to Determine |Vcb| 1st Lepton Energy Moment Preliminary 2nd Lepton Energy Moment Preliminary 1st Photon Energy Moment 2nd Photon Energy Moment Preliminary Preliminary Alex Smith – University of Minnesota

27. Combined Fit to Determine |Vcb| Preliminary 1stq2 Moment 1st Hadronic Mass Moment 2nd Hadronic Mass Moment Preliminary Preliminary Alex Smith – University of Minnesota

28. Combined Fit to Determine |Vcb| Preliminary measurement key Alex Smith – University of Minnesota

29. Measurement of |Vcb| and HQET parameters, including mb(m), mc(m), mp2(m) at m=1 GeV Expect to reduce experimental errors significantly with additional measurements Theory errors under study and not shown or included in fit Expected to be >= experimental errors Combined Fit to Determine |Vcb| Preliminary Alex Smith – University of Minnesota

30. Summary • Potential to significantly improve measurement of |Vcb| • Experimental errors expected to be less than 2% • Theoretical errors expected to be comparable to experimental errors • Theoretical models will benefit from experimental constraints on higher order parameters • Many improvements to analysis in progress: • 3rd lepton energy moments– work in progress • Include more 1st and 2nd lepton energy moment measurements in fit • 2ndq2 moments – should have corrections soon • Complementary sensitivity to parameters • Improved BXsg moments – soon • Critical constraint on mb • Include theoretical uncertainties in fit– almost ready • CLEO has measured several different moments in a single experiment • Complementary to and of comparable precision to public BaBar measurements Alex Smith – University of Minnesota