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Semileptonic Decays from Belle

This work by Youngjoon Kwon from Yonsei University presents analyses of semileptonic decays observed at the Belle experiment. It discusses the measurements of the CKM matrix elements Vub and Vcb, highlighting the importance of precise measurements in testing the Standard Model of particle physics. The study emphasizes the challenges and methodologies involved in measuring these transitions, including both inclusive and exclusive decay modes, and addresses theoretical uncertainties inherent in the analyses.

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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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