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Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University

The First Evidence of B  t n from Belle & Future Prospect. As a contribution to WG2 (neutrino modes) Ref: K.Ikado’s talk at FPCP06 hep-ex/0604018. Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University. May 15, 2006 “Flavour in the LHC era” @ CERN.

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Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University

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  1. The First Evidence of Bt n from Belle & Future Prospect As a contribution to WG2 (neutrino modes) Ref: K.Ikado’s talk at FPCP06 hep-ex/0604018 Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University May 15, 2006 “Flavour in the LHC era” @ CERN

  2. Bt n (within the SM) • Proceed via W annihilation in the SM. • Branching fraction is given by • Provide information of fB|Vub| • |Vub| from BXu l n fB cf) Lattice (d~10%) • Br(Btn)/Dmd |Vub| / |Vtd| • Expected branching fraction HFAG [hep-ex/0603003] HPQCD [PRL95,212001(2005)] Toru Iijima @ Flavour in the LHC era

  3. H+/W+ t+ c b H+/W+ t+ nt Bt X as a Probe to Charged Higgs Charged Higgs contribution to B decays • Leptonic: Bt n • Semileptonic: BD t n Br(SM) ~ 9 x 10-5 Br(SM) ~ 8 x 10-3 Decay amplitude Tauonic decay is the most sensitive !

  4. Search for Btn • Btn is important for both SM and BSM. • Purely leptonic  Theoretically very clean • More than two n’s  Experimentally very challenging. • Its detection is a milestone of B physics. B factories LEP First Evidence ! April 2006 Toru Iijima @ Flavour in the LHC era

  5. n n Y(4S) B- B+ p+ Btn Analysis Concepts • B decays with missing neutrinos lack the kinematic constraints which are used to separate signal events from backgrounds (Mbc and DE). • Reconstruct the decay of the non-signal B (tagging), then look for the signal decay in whatever is left over More than 2 neutrinos appear in B tn decay Tagging side : Fully reconstruct hadronic modes Signal side : Reconstruct particles from t decay Toru Iijima @ Flavour in the LHC era

  6. Features with Fully Reconstructed B Tag • Pros: Offline B meson Beam • B momentum is known.  Resolution of Mmiss2 can be significantly improved. • B-flavor/charge is known.  We can treat charged & neutral B separately  Large background reduction • Cons: Low statistics • Tagging efficiency : 0.2 - 0.3% Mmiss2 for B-D0 m- n (MC) w/o B momentum with B momentum  Large lum. required ! Toru Iijima @ Flavour in the LHC era

  7. Fully Reconstructed Tag at Belle (447M BB) ~ 180 channels used 7 modes 6 modes 2 modes • Beam constrained mass N= 680k eff.= 0.29% purity = 57% N = 412 k eff.= 0.19% purity = 52% m ~ 5.28 GeV/c2 s~ 3 MeV/c2 due to s(Ebeam) ~10% for feed-across between B+ and B0 Neutral B Charged B Signal region : -0.08 < DE < 0.06 GeV, Mbc > 5.27 GeV/c2 Toru Iijima @ Flavour in the LHC era

  8. Signal Selection (1) • t lepton is identified in the 5 decay modes. • Signal selection criteria. • Signal-side efficiency including t decay br.) • All selection criteria were optimized before examining the signal region (blind analysis). 81% of all t decay modes 32.92 0.12% Toru Iijima @ Flavour in the LHC era

  9. Signal Selection (2) • Extra neutral energy in calorimeter EECL • Most powerful variable for separating signal and background • Total calorimeter energy from the neutral clusters which are not associated with the tag B Minimum energy threshold • Barrel : 50 MeV • For(Back)ward endcap : 100(150) MeV Zero or small value of EECL arising only from beam background Higher EECL due to additional neutral clusters MC includes overlay of random trigger data to reproduce beam backgrounds. Toru Iijima @ Flavour in the LHC era

  10. Signal Selection (3) • Extra neutral energy EECL Validationby double tagged sample (control sample); • Btag is fully reconstructed • Bsig is semileptonic decays B+ D(*)0 X+ (fully reconstruction) B- D*0 l-n D0p0 K-p+ K-p+ p-p+ Purity ~ 90% Toru Iijima @ Flavour in the LHC era

  11. Background Estimation MC : 94.2  8.0 Data : 96 MC : 89.6  8.0 Data : 93 MC : 41.3  6.2 Data : 43 MC : 18.5  4.1 Data : 21 MC : 23.3  4.7 Data : 21 Sideband Total MC : 267  14 Data : 274 Large MC samples for e+e- BB, qq, Xuln, Xu tn,t+ t- , and rare B decays are used (including beam-background). Majority come from BD(*) X l n (~90%) + Xu l n/rare (~10%). Toru Iijima @ Flavour in the LHC era

  12. Result: Opening the Box ! • The signal regions are examined after finalizing all of the selection criteria. 414 fb-1 # estimated background and observed events in the signal region Observe excess in signal region ! Toru Iijima @ Flavour in the LHC era

  13. Btn Candidate Event B+g D0 p+ K+p- p+p- B-gt - n e-nn Toru Iijima @ Flavour in the LHC era

  14. Pmiss Mbc Verification of the Signal (1) • For events in the EECL signal region, distribution of event selection variables other than EECL are verified. • They are consistent with MC expectation for Btn signal + background. Btn signal Background Toru Iijima @ Flavour in the LHC era

  15. Verification of the Signal(2) • About 30% of background have neutral cluster in the KLM detector (KL candidates). • The excess remains after requiring KL veto. KL in coincidence. KL in veto EECL EECL • We do not use this cut in the result, to avoid introducing large systematic error due to KL detection efficiency uncertainty. Toru Iijima @ Flavour in the LHC era

  16. Fit Results • The final results are deduced by unbinned likelihood fit to the obtained EECL distributions. Signal + background S : Significance with systematics Btn Signal Background +6.7 - 5.7 Observe 21.2 events with a significance of 4.2s Signal shape : Gauss + exponential Background shape : second-order polynomial Toru Iijima @ Flavour in the LHC era

  17. Systematic Uncertainty • Signal selection efficiencies • Tag reconstruction efficiency : 10.5% Difference of yields between data and MC in the B- D*0l-ncontrol sample • Number of BB : 1% • Signal yield : • signal shape ambiguity estimated by varying the signal PDF parameters • BG shape : changing PDF • Total systematic uncertainty +12% -10% +17% -15% Toru Iijima @ Flavour in the LHC era

  18. Btn Branching Fraction • Branching fractions are calculated by • All t decay modes combined Extracted branching fraction for each t decay mode SM : B(Btn)=(1.59  0.40)×10-4 Result is consistent with SM prediction within error Toru Iijima @ Flavour in the LHC era

  19. fB Extraction • Product of B meson decay constant fB and CKM matrix element |Vub| • Using |Vub| = (4.39  0.33)×10-3 from HFAG 11% = 8%(exp.) + 8%(Vub) 14% fB = 0.216  0.022 GeV [HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]

  20. Constraint for Improved measurement will help. Constraints on |Vub|/|Vtd| • Constraint in the (r,h) plane from the Btnbranching fraction and Dmd Toru Iijima @ Flavour in the LHC era

  21. B A rH 2s B 95.5%C.L. exclusion boundaries Constraints on Charged Higgs A Toru Iijima @ Flavour in the LHC era

  22. Future Prospect (1) • Br(Bt n) measurement: Further accumulation of luminosity help to reduce both statistical and systematic errors errors. • Some of the major systematic errors come from limited statistics of the control sample. • |Vub| measurement: < 5% in future is an realistic goal. • fB from theory ~10% now  5% ? Note: Assumption in the following plots Toru Iijima @ Flavour in the LHC era

  23. If D|Vub| = 0 & DfB = 0 Future Prospect (2) 95.5%C.L. exclusion boundaries DfB(LQCD) = 5% 5ab -1 rH 2s 50ab -1 rH

  24. Future Prospect (3) Charged Higgs Mass Reach (95%CL @ tanb=30) 1TeV Only exp. error (DVub=0%, DfB=0%) DVub=2.5%, DfB=2.5% Mass Reach (GeV) DVub=5%, DfB=5% Luminsoity(ab-1) 5 10 20 30 40 50 Toru Iijima @ Flavour in the LHC era

  25. fD measurements Toru Iijima @ Flavour in the LHC era

  26. Summary • We have seen the evidence of B t n with 414fb-1 data at Belle. • The first evidence of purely leptonic B decays. • Branching fraction • B decay constant • Constraint on charged Higgs. • O(ab-1) data, together with improved fB and |Vub|, will allow us to probe large tanb-mass space of charged Higgs. Probe up to ~200GeV at tanb=30 Toru Iijima @ Flavour in the LHC era

  27. Backup Slides Toru Iijima @ Flavour in the LHC era

  28. Fit Result (2) • Likelihood fit results for each t decay mode. Signal + background Background Signal Toru Iijima @ Flavour in the LHC era

  29. Fit Results (3) • Likelihood distributions for each t decay mode. Toru Iijima @ Flavour in the LHC era

  30. Future Prospect (5ab-1) 95.5%C.L. exclusion boundaries DfB(LQCD) = 10% rH 2s DfB(LQCD) = 5% rH 2s Toru Iijima @ Flavour in the LHC era

  31. Full Reconstruction Method • Fully reconstruct one of the B’s to tag • B production • B flavor/charge • B momentum Decays of interests BXu l n, BK n n BDtn, tn B e- (8GeV) e+(3.5GeV) Υ(4S) p full (0.1~0.3%) reconstruction BDp etc. B Single B meson beam in offline ! Powerful tools for B decays w/ neutrinos Toru Iijima @ Flavour in the LHC era

  32. c b H+/W+ t+ nt Search for Charged Higgs • BDtn (semileptonic decay) Band width from form-factor uncertainty • Full reconstruction tag • Signal  large missing mass • Expected at 5ab-1 Toru Iijima @ Flavour in the LHC era

  33. Form factor error Constraint to Charged Higgs • Once branching fraction is measured, we can constrain R. M.Tanaka, Z.Phys. C67 (1995) 321 r can be determined experimentally by B semiletonic decays at 5ab-1 Toru Iijima @ Flavour in the LHC era

  34. Sensitivity for Charged Higgs Constraint from BXsg BDtn D(Form-factor) ~5% D(Form-factor) ~15% Btn (present) LHC 100fb-1 D(form-factor) can be reduced with the present BDmn data. Toru Iijima @ Flavour in the LHC era

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