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Semileptonic B physics at CLEO

Semileptonic B physics at CLEO. CLEO- c Collaboration. Ron Poling University of Minnesota CLEO Collaboration. CESR and CLEO: 23 years of B Physics. Three generations of detectors, ~170 Ph.D.’s, ~360 papers. V cb or V ub.

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Semileptonic B physics at CLEO

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  1. Semileptonic B physics at CLEO CLEO-c Collaboration Ron Poling University of Minnesota CLEO Collaboration

  2. CESR and CLEO: 23 years of B Physics Three generations of detectors, ~170 Ph.D.’s, ~360 papers Ron Poling WIN03 October 7, 2003

  3. Vcb or Vub Goal: redundant determinations of sides and angles of the Unitarity Triangle(s) CLEO’s Role: Measure UT sides through |Vcb| and |Vub| in semileptonic B decays. Detailed studies to guide interpretation and help clear the “fog” of nonperturbative effects. Challenging experimentally and theoretically. The Global Program of CKM Tests Ron Poling WIN03 October 7, 2003

  4. B Semileptonic Branching Fraction CLEO - Preliminary • CLEO II: 10 fb-1 at (4S) • Mature, well-understood detector, data, Monte Carlo, generators, etc. • Lepton-Tagged Analysis • ptag>1.4 GeV/c plus accompanying electron with pe>0.6 GeV/c. • Charge, angular correlations to separate primary (BXe) from secondary (BD Ye). • Refined electron ID, background and efficiency determinations. • Maximize understanding and minimize momentum dependence. Preliminary:B(BXe)=(10.88  0.08  0.33)% Ron Poling WIN03 October 7, 2003

  5. BSL – Still small-ish, but consistent • Good agreement among different techniques, experiments. • Measurements at (4S) have come up and LEP Z0 average has come down. • Most recent LEP fit result is (10.590.22)% Ron Poling WIN03 October 7, 2003

  6. Vcb or Vub We idealize them as… The real picture is… View of b decay obscured by… Hadronic effects describable by both perturbative and nonperturbative QCD. Uncertainty about our assumption of quark-hadron duality. Available tools include Heavy Quark Effective Theory and Lattice QCD. Must be validated by experiment. The Reality of Semileptonic B Decays Ron Poling WIN03 October 7, 2003

  7. HQET+OPE • Expresses observables of inclusive b decay as expansions in inverse powers of MB (Voloshin +Shifman, …). • One parameter at order QCD/MB: • ~ MB – mb is the energy of light-quark and gluon degrees of freedom in the B meson. • Two parameters at order 2QCD/M2B: • 1 – negative of the average b-quark momentum squared. • 2 – energy of the hyperfine interaction of the b spin with the light degrees of freedom (from B*-B splitting: 2 = (0.128  0.010) GeV). • Six more parameters at order 3QCD/M3B(Gremm and Kapustin): • 1, 2, T1, T2, T3, T4 (not all independent). • Meaning of parameters depends on choices: order of perturbative (0(s/)2 ) and nonperturbative (1/M3B) expansions and mass scheme. Consistency required. |Vcb| is what counts! Ron Poling WIN03 October 7, 2003

  8. Data from different processes will tell us if this approach provides a coherent picture of inclusive B decays. MOMENTS, INC. – CLEO Branch • BXs Photon-Energy Moments • BXl Lepton-Energy Moments • BXl Hadronic Recoil Mass Moments First and second moments, different lepton-energy ranges… Lots of complementary information. Ron Poling WIN03 October 7, 2003

  9. Use all available tools! Traditional shape variables. Pseudo-reconstruction: demand consistency with BK(n) Use neural net to compute signal probability and measure spectrum of “weights.” Subtract continuum with below-(4S) data. Subtract backgrounds with Monte Carlo, informed by data wherever possible. Measuring BXs Photon-energy spectrum at (4S) Continuum must be suppressed. Ron Poling WIN03 October 7, 2003

  10. CLEO II – 10 fb-1 PRL 87, 251807 (2001) Hard measurement, simple interpretation: Almost two-body, with broadening by Fermi motion, gluon bremsstrahlung, boost of B’s at (4S) <E> gives nearly direct access to . Measuring BXs Next, measure the moments of the E spectrum by fitting to model of Ali-Greub or HQT calculation of Kagan-Neubert: Ron Poling WIN03 October 7, 2003

  11. Select events with leptons with 1.5 < pl < 2.5 GeV/c “ reconstruction” to measure p. Calculate approximate hadronic recoil mass using l (take advantage of pBsmall): Construct continuum-subtracted spectrum and fit to mixture: BDl (CLEO FF’s) BD*l (CLEO FF’s) High-mass, nonresonant by models (ISGW2, Goity/Roberts) Use fit components to compute moments: Hadronic Mass Moments in BXcl PRL 88, 251808 (2001) = 0.2510.023 0.062 GeV2 = 0.6390.056 0.178 GeV2 Ron Poling WIN03 October 7, 2003

  12. Interpreting the Moments • First moments E and MX2- MD2 fitted to extract  and 1. • Combined solution is  = 0.350.0700.10 GeV 1 = -0.2360.0710.078 GeV2 • Precise meaning of parameters is scheme- and order-dependent; these are to order 1/MB3, order 0s2 in MS scheme. Ron Poling WIN03 October 7, 2003

  13. Extracting |Vcb| from (BXcl) • Ingredients: • (BXcl) = (10.80.3)% (CLEO) • B0andB(PDG), f+/ f00 (CLEO) • SL = (0.44  0.02)  10-10 MeV • Result: • |Vcb| = 0.041  0.0005  0.0007  0.0009 • Overall precision: ~3% + quark-hadron duality. Ron Poling WIN03 October 7, 2003

  14. |Vcb| from BD*l d/dw PRL 88, 251808 (2001) 0.03880.0011 |Vcb|=(42.6±1.2±2.3)10-3 Ron Poling WIN03 October 7, 2003

  15. New and Improved Measurement of the Hadronic Mass Moments in BXcl hep-ex/0307081 - Contributed to Lepton-Photon 2003 • Compute recoiling hadronic mass from charged lepton and neutrino kinematics - neutrino “detection.” • Near hermeticity of CLEO II  Neutrino=“What’s missing” Fit 3-dimensional differential decay rate, extract hadronic mass squared as a function of lepton-energy cut (pl > 1 GeV/c). Ron Poling WIN03 October 7, 2003

  16. Fit Projections • Selection criteria: • Cuts to enhance  reconstruction • Continuum suppression • Efficiency ~2% for BXcl • Sample to fit: 122K events • Components of fit: • BDl • BD*l • BD**lISGW2 • B(Xc)NRlGoity/Roberts • BXul ISGW2+NR • SecondariesCLEO MC • Fake Leptons, Continuum fixed with data  HQET+measured FFs Ron Poling WIN03 October 7, 2003

  17. PRELIMINARY PRELIMINARY Results Fits Mode-by-Mode BRs + Generator-Level Info (Fraction above pl cut, moment value for that cut.)  Moment Value for BXcl DELPHI: energy and hadronic mass moments for full lepton-energy spectrum. hep-ph/0210319 • Consistent with previous CLEO measurements, BaBar summer ’03 • Interpretation continues Ron Poling WIN03 October 7, 2003

  18. e BXclEnergy MomentsPRD 67, 072001 (2003) Pending…El moments down to 0.6 GeV Ron Poling WIN03 October 7, 2003

  19. End-point technique: Isolate BXul by looking above (and just below) the BXcl kinematic limit. Used for bu discovery (CLEO, ARGUS) and CLEO 93: |Vub|/|Vcb|= 0.080.02 Significant model dependence. Can now do better: Better knowledge of BXcl. BXs helps determine fraction of spectrum in end point. Improved Inclusive Measurement of |Vub| BXs spectrum  shape function  fu Ron Poling WIN03 October 7, 2003

  20. 2.0 < pl <2.6 GeV/c Suppress continuum with neural net (energy flow w.r.t. lepton). Less q2- and M(Xu)-dependent. Estimate BXcl by fitting inclusive spectrum. Components reflect state-of-the-art on form factors, b.r.’s, etc. Trade-off: BXcl uncertainty vs. spectral-fraction uncertainty. PRL 88, 231803 (2002) Measuring BXul ON b cl OFF bul excess Ron Poling WIN03 October 7, 2003

  21. Hoang, Ligeti, Manohar; Uraltsev: Determine from B Xs shape-function fits (Kagan-Neubert). Extracting |Vub| In preparation: Paper with details of fits for shape-function parameters and fu values for phase-space regions other than just end point. Ron Poling WIN03 October 7, 2003

  22. Exclusive reconstruction of B(///)l  through neutrino “detection.” Near hermeticity of CLEO II  Neutrino=“What’s missing” Signal defined by… Branching Fractions and q2 Dependenceof Bl and B()l and Extraction of |Vub| hep-ex/0304019 to be published in PRD Ron Poling WIN03 October 7, 2003

  23. CLEO II 10 fb-1 • Event selection to enhance  reconstruction, suppress continuum • Fit Mml and E in three bins in q2 to find branching fractions Bl (pl > 1.0 GeV/c) Bl (pl > 1.5 GeV/c) Ron Poling WIN03 October 7, 2003

  24. Bl • Extracting |Vub| • Fit d/dq2 • Discriminates among FFs • Bl • FF dependence is small • Disfavors ISGW2 • Bl • Larger FF dependencegreater model uncertainty in |Vub| Bl Ron Poling WIN03 October 7, 2003

  25. RESULTS Ron Poling WIN03 October 7, 2003

  26. 90% c. l. contours Comparisons and CKM Impact |Vub|/10-3 Ron Poling WIN03 October 7, 2003

  27. Perspectives and Prospects • CLEO is still contributing on |Vub| and |Vcb|. • Sample smaller than B factories, but well understood with mature tools. • We’re all limited by theoretical uncertainties. • Continuing and forthcoming CLEO CKM-related measurements: • Completion of moment measurements, coordinated fits of all available inputs. • Inclusive bul for all CLEO II and CLEO III via multidimensional fit and bigger phase-space acceptance. • CESR-c/CLEO-c will have significant impact on CKM. See the upcoming of Karl Ecklund. Ron Poling WIN03 October 7, 2003

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