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Semileptonic B physics at CLEO

This presentation by Ron Poling from the CLEO Collaboration details insights gained over 23 years of B-physics research, emphasizing semileptonic B decays. The CLEO experiment has played a crucial role in measuring CKM parameters, particularly |Vcb| and |Vub|, through redundant determinations of the Unitarity Triangle's sides and angles. The talk outlines experimental challenges, the importance of nonperturbative QCD effects, and highlights collaborative efforts that have resulted in significant findings and publications, underscoring the evolution of B-physics research.

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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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