Rare B Decays with “Missing Energy”

1. Rare B Decays with “Missing Energy” Representing the Belle Collaboration Will discuss experimental results from Belle on Bν (BELLE-CONF-0671) and BK*νν(BELLE-CONF-0627) Tom Browder (University of Hawaii) All results discussed here are preliminary.

2. B decay constant Motivation for B++ν Sensitivity to new physics from charged Higgs if the B decay constant is known Most stringent published limit: BF(B++ν) < 2.6 x 10-4 (BaBar) B. Aubert et al., PRD 73, 057101 (2006)

3. e+ (4S) B- B+ ne n n B-X B++, +e+e Why measuring Bνis non-trivial Most of the sensitivity is from tau modes with 1-prong The experimental signature is rather difficult: B decays to a single charged track + nothing

4. Belle’s sample of B tags (447 x 106 BB) 7 modes ~ 180 channels reconstructed 6 modes 2 modes Signal region : -0.08 < DE < 0.06 GeV, Mbc > 5.27 GeV/c2 N=680 K Eff=0.29% Purity =57% N=412 K Eff=0.19% Purity =52% m ~ 5.28 GeV/c2 s~ 3 MeV/c2 from s(Ebeam) ~10% feed-across between B+ and B0 Charged B’s Neutral B’s Beam constrained mass distn’s

5. Outline of B νexperimental analysis • Reconstruct one B (Btag) in a charged hadronic b  c mode (remove tag’s decay products from consideration.) • Little or no extra electromagnetic calorimeter energy (EECL) . Beam-related backgrounds modeled in MC using random trigger data runs. ·For B X n known EB, mB, small pB •  narrow missing mass distn. (mn~0) ·Two missing neutrinos, large missing p (cut depends on  decay mode 0.2 GeV-1.8 GeV)

6. Outline of experimental analysis (cont’d) • The tlepton is identified in the 5 decay modes: • Signal-side efficiency including t decay BFs) • All selection criteria were optimized before examining the signal region (a.k.a. blind analysis) • Fit the extra energy distribution (EECL), the signal peaks near zero 81% of all t decays 15.81 0.05%

7. Consistency Check with BD* lν • Extra neutral energy EECL Validationwith double tagged sample (control sample); • Btag is fully reconstructed • Bsig is a semileptonic decay Calibration data B+ D(*)0 X+ (fully reconstruction) B- D*0 l-n D0p0 K-p+ K-p+ p-p+ Purity ~ 90% Extra energy in the calorimeter

8. Example of a B ν candidate Tag: BD0, D0K

9. Evidence for B+ν (Belle) BtagD(*)[p,r,a1,Ds(*)] 680k tags, 55% pure. 5 t decay modes 447 106 B pairs Find signal events from a fit to a sample of 54 events. 4.6s stat. significance w/o systematics, After including systematics (dominated by bkg), the significance decreases to 3.5σ MC studies show there is a small peaking bkg in the 0  and 0  modes. Extra Calorimeter Energy

10. Byields broken down by  decay mode (stat sig only) For the first 3 modes, the background is fitted with a 2nd order polynomial plus a small Gaussian peaking component.

11. Error in the efficiency calculation Due to a coding error, the efficiency quoted in the 1st Belle preliminary result was incorrect. The data plots and event sample are unchanged. However, fB and the branching fraction must be changed. This mistake was not detected when checking the BD* l control sample or in the internal review process. New value (Preliminary) Previous value

12. Direct experimental determination of fB • Product of B meson decay constant fB and CKM matrix element |Vub| • Using |Vub| = (4.39  0.33)×10-3 from HFAG ( Belle) 15% 14% = 12%(exp.) + 8%(Vub) fB = 216  22 MeV (an unquenched lattice calc.) [HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]

13. Constraints on the charged Higgs mass Assume fB and |Vub | are known, take the ratio to the SM BF. rH=1.130.51

14. Motivation for BK* (bs with 2 neutrinos) BSM: New particles in the loop Other weakly coupled particles: light dark matter SM: BF(BK* ) ~1.3 x 10-5(Buchalla, Hiller, Isidori) PRD 63, 014015 c.f. SM: BF(BK-) ~4 x 10-6 [Belle preliminary (275 x 106 B Bbar) : BF(BK-) <3.6 x 10-5] to be updated soon

15. DAMA NaI 3s Region CDMS 04 CDMS 05 BK(*)ννare particularly interesting and challenging modes (Bν is even a small background) The experimental signature is BK + Nothing The “nothing” can also be light dark matter (mass of order (1 GeV)) (see papers by M. Pospelov et al.) (But need to optimize pK cut) C. Bird et al PRL 93 201803 .(T. Adams et al. PRL 87 041801;A. Dedes et al., PRD 65 015001) Direct dark-matter searches cannot see M<10 GeV region

16. Search for BK* (532 x 106 B Bbar pairs) Result from a blind analysis. BELLE-CONF-0627 (1.7σ stat. significance) Sideband = 19 MC expectation = 18.73.3 SM (Buchalla, Hiller, Isidori) 1.3 x 10-5 Extra Calorimeter Energy (GeV) (at 90% C.L)

17. Search for BK* (properties of candidates) b  c background rare B background (x 15 data) udsc background Signal x 20 combined background Data KπInv. mass

18. Search for BK* (properties of candidates) b  c background rare B background (x 15 data set) udsc background Signal shape combined background Need more bc MC (only 2 x data) Data P*_K* K* momentum distribution

19. Event display for a BK* candidate due to an identified background (BK*γ) Tag Side B  D+ a1- D+  K-π+π+ a1- ρ0π- , ρ0 π+π- π+ K- Missing mass ~ 0 (Hard photon is lost in the barrel-endcap calorimeter gap) γ MC: Expected bkg from this source ~0.3 evts.

20. If D|Vub| = 0 & DfB = 0 Future Prospects: B 95.5%C.L. exclusion boundaries DfB(LQCD) = 5% Extrapolations (T.Iijima) 50ab -1 rH

21. c b H+/W+ t+ nt Future Prospects: Other probes of charged Higgs • Semileptonic: BD(*)t n Decay amplitude Expected BF(SM)~ 8 x 10-3 Multiple neutrinos, low momentum lepton (use e’s), large bkg but still might be possible with enough data.

22. Some modes are very difficult at hadron colliders MC extrapolation to 50 ab-1 5s Observation of B±gK±n n (compare to K++ννand KLgp0nn) MC Belle result on Bνshows that B to one prong decays can be measured. SM pred: G. Buchalla, G. Hiller, G. Isidori (PRD 63 014015 ) Extra EM calorimeter energy Super B LoI Fig.4.18

23. Conclusions on “Missing Energy Decays” • Evidence for Bνand experimental determination of fB (preliminary result has been updated) • Search for BK*  (UL is still a factor of 10 above the SM range) • Further dramatic progress (e.g. signals for BK(*)νν) will require Super B Factory class luminosity.

24. Backup Slides

25. Contributions to systematic error for B

26. Peaking Backgrounds in B Tau tagging mode Tau tagging mode

27. Fits to individual B  decay modes (updated for ICHEP06)

28. Requirements in Bν analysis • The tlepton 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 15.81 0.05%

29. 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

30. 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 a large systematic error due to the uncertainty in KL detection efficiency.

31. Selection Requirements for BK*  MC signal and bkg distributions,

32. Tag Side B  D+ a1- D+  K-π+π+ a1- ρ0π- , ρ0 π+π- π+ tagB tagB tagB K- tagB tagB tagB γ