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Semileptonic Decays from Belle

Semileptonic Decays from Belle. Youngjoon Kwon Yonsei Univ. / Belle. Contents. Introduction A nalyses for V ub Inclusive B  X u l n with full-recon. Inclusive B  X u l n with end-point Exclusive B  X u l n with semileptonic tag. ( prelim. )

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Semileptonic Decays from Belle

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  1. Semileptonic Decays from Belle Youngjoon Kwon Yonsei Univ./ Belle

  2. Contents • Introduction • Analyses for Vub • Inclusive B  Xu l n with full-recon. • Inclusive B  Xu l n with end-point • Exclusive B  Xu l n with semileptonic tag. (prelim.) • Analyses towards precise Vcb • Inclusive B  X e n with full-recon. • B  X l n hadronic mass moments (prelim.) • B  X l n lepton energy moments (prelim.) PRL submitted, hep-ex/0505088 PLB accepted, hep-ex/0504046 PLB 614, 27 (2005) Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  3. Motivation • Fundamental free parameters • Majority of free parameters in the SM are related to quark (and lepton) flavors : masses and mixings • Quark flavor mixing through CKM matrix • Unitarity triangle • Direct test of CP violation mechanism in SM • Vub: still a weak link in CKM test • Vcb : as fundamental as Vub • Super-high precision, experimentally • A good testing ground of strong int. theory Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  4. Issues in Vub measurement • Use B  Xu l n (semileptonic) • Cleaner, better understood than B  hadronic • More accessible than B  leptonic • Inclusive and Exclusive • Experimentally challenging • Tight selection criteria results in Limited phase space  Extra theoretical uncertainties (from extrapolation) Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  5. Variables to suppress b  c l n (10% phase sp.) (~80%) (~30%) Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  6. Inclusive B  Xu l n with End-point

  7. Main features • Measure DB(B  Xu e n, pe > pcut) • Kinematic selection • pe > pcut • pcut = 1.9, 2.0, 2.1, 2.2, 2.3 and 2.4 GeV/c • No requirement other than on the • signal electron • high statistics • Large background from B  Xc e n • bkg. sys. uncertainty OPE breaks down  need shape ftn.! Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  8. b-quark Shape Function • What is it? • b-quark Fermi motion inside the B-meson • How to get it? • Universal at leading order for all b light quark transitions • Use E(g) in B  Xs g Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  9. Three models for SF Neubert & Paz, hep-ph/0504071

  10. Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  11. Event Selection • Hadronic events • Electrons in the barrel region • eff. ~ 94%; fake rate ~ 0.13% • J/y, y(2S), g, p0 veto • Continuum suppression • Fox-Wolfram moment • Fisher disc. for energy-flow variables • |cos qth| < 0.75 • as q2 independent as possible • Background estimated by • b cMC and Off-resonance Data • low-p region for check 1.5 < pe < pcut (GeV/c) Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  12. E(e) spectrum for B  Xu e n Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  13. DB – partial BF • Two methods for DBVub • Standard method(DFN, JHEP 9906, 017) • New method(BLNP, NP B699 (2004))

  14. Vub from DB DFN BLNP

  15. Inclusive B  Xu l n with Full-Recon.

  16. Full Reconstruction 4.2105 evts./253 fb-1 effic. = 0.33% purity = 62% 2.5105 evts./253 fb-1 effic. = 0.21% purity = 59% Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  17. Signal selection • Lepton Selection • p > 1 GeV/c • leptons in the barrel region • J/y, g, p0 veto • Correct charge for B+ candidate • No other lepton Nsl= (9.15  0.05) x 104 • For b u • Total charge = 0 • No reconstructed KS or K Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  18. Kinematic selections (New) Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  19. (1) MX < 1.7 GeV • Each bin content is calculated from Mbc fit • 2-component fit to extract N(bu)

  20. Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  21. (2) MX < 1.7 GeV & q2 > 8 GeV2

  22. (3) P+ < 0.66 GeV • First measurement using P+

  23. Signal Yield & DB Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  24. Vub from DB • New method • Vub directly from DB R by Bosch, Lange, Neubert, Paz, NPB699 (2004) with an improved treatment of shape-function effects + weak annihilation effects estimated Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  25. Exclusive B  Xu l n with S.L. tag

  26. good mod. poor low middle high Experimental Strategy Unique opportunity at e+e- B-factory! Bp l n / r l n (140fb-1) ICHEP04 preliminary hep-ex/0408145 S/N Full recon. D(*) l n tag Bw l n (78fb-1) PRL 93, 131803 (2004) advanced n recon. + p l n / r l n (preliminary) Lum. trad. n recon. Eff. How well can we measure the q2 dist. (for p l n) ?

  27. Analysis Method Tag side reconstruction 4 decay modes 7 decay modes Signal side reconstruction or Kinematics of double semileptonic decay Back-to-back correlation of the two B’sconstrains their direction to the intersection of the 2 cones. To have intersection, need 2-fold ambiguity q2 calculated neglecting the B motion in U(4S) q2 resolution = 0.75 GeV2

  28. Calibration with Bsig→D*ln Decays • Validity of the method for double semileptonic decay detection has been tested with M(K+p-p-) on the signal side xB2 distribution Nobs=14712 ( Nexpected =165) Dots: Data Histo: MC xB2 M(Kpp) GeV/c2 • The ratio Nobs/Nexpected = 0.89 0.08 is used to correct the MC efficiency for p l n and r l ndetection. The method works !

  29. Signal Extraction • q2 distribution is extracted by fitting the (mX,x2) distrib. for three q2 intervals. mX (GeV/c2) q2:8-16GeV2 q2>16GeV2 q2<8GeV2 • Fitting components: pln, r ln, other Xu ln, and BB • PDF’s are based on MC. • Constraint for extracted Br: • Br(pln)+Br(r ln)+Br(other Xu ln)=Br(Xu ln) 8213 6520 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  30. Results

  31. Vub from exclusive B  Xu l n 140 fb-1

  32. Analyses towards precise Vcb • Inclusive B  X e n (0th moment) • B  X l n hadronic mass moments (prelim.) • B  X l n lepton energy moments (prelim.) PLB 614, 27 (2005)

  33. PLB 614, 27 (2005)

  34. B  X l n moments • Leptonic and hadronic moments • Needed for global fit for precise Vcb • Common features • Preliminary with140 fb-1 • Full-recon. in the tag side • Boost from Btag • QED correction by PHOTOS • Mixing correction • Unfolded by SVD method Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  35. Leptonic moments

  36. Hadronic moments Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

  37. Hadronic moments

  38. Belle Vub Summary

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