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

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

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

Belle’s sample of B tags (447 x 10 6 BB) 7 modes 6 modes 2 modes Beam constrained mass distn’s Signal region : GeV/c 2 ~10% feed-across between B + and B 0 m ~ 5.28 GeV/c 2  ~ 3 MeV/c 2 from  (E beam ) ~ 180 channels reconstructed Charged B ’ s Neutral B ’ s N=680 K Eff=0.29% Purity =57% N=412 K Eff=0.19% Purity =52%

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

Outline of experimental analysis (cont’d) The  lepton is identified in the 5 decay modes: Signal-side efficiency including  decay BFs) All selection criteria were optimized before examining the signal region (a.k.a. blind analysis) Fit the extra energy distribution (E ECL ), the signal peaks near zero 81% of all  decays  0.05%

Consistency Check with B  D * l ν Extra neutral energy E ECL Validation with double tagged sample (control sample); –B tag is fully reconstructed –B sig is a semileptonic decay B +  D (*)0 X + (fully reconstruction) B -  D *0 B -  D *0 l - D 0  D 0  0 K -  + K -  + K -  +  -  + K -  +  -  + B+B-B+B- 494  18 B0B0B0B0 7.9  2.2 Total502  18 Data458 Purity ~ 90% Extra energy in the calorimeter Calibration data

Example of a B   ν candidate Tag: B  D 0 , D 0  K 

Evidence for B +   ν (Belle) Find signal events from a fit to a sample of 54 events. 4.6  stat. significance w/o systematics, 447  10 6 B pairs B tag  D (*) [ ,a 1,D s (*) ] 680k tags, 55% pure. 5  decay modes MC studies show there is a small peaking bkg in the    0 and    0 modes. After including systematics (dominated by bkg), the significance decreases to 3.5σ Extra Calorimeter Energy

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

Error in the efficiency calculation Due to a coding error, the efficiency quoted in the 1 st Belle preliminary result was incorrect. The data plots and event sample are unchanged. However, f B 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. Previous value New value (Preliminary)

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

Constraints on the charged Higgs mass r H =1.13  0.51 Assume f B and |V ub | are known, take the ratio to the SM BF.

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

B  K (*) νν are 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 p K cut) DAMA NaI 3  Region CDMS 04 CDMS 05 Direct dark-matter searches cannot see M<10 GeV region C. Bird et al PRL (T. Adams et al. PRL ;A. Dedes et al., PRD )

Search for B  K * (532 x 10 6 B Bbar pairs) (at 90% C.L) Extra Calorimeter Energy (GeV) (1.7σ stat. significance) Sideband = 19 MC expectation = 18.7  3.3 SM (Buchalla, Hiller, Isidori) 1.3 x BELLE-CONF Result from a blind analysis.

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

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

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

20 Future Prospects: B    f B (LQCD) = 5% 95.5%C.L. exclusion boundaries rHrH 50ab -1 If  |V ub | = 0 &  f B = 0 Lum.  B(B   ) exp  |V ub | 414 fb -1 36%7.5% 5 ab -1 10%5.8% 50 ab -1 3%4.4% Extrapolations (T.Iijima)

21 Future Prospects: Other probes of charged Higgs c b  H/WH/W  Decay amplitude Expected BF(SM)~ 8 x Semileptonic: B  D (*)  Multiple neutrinos, low momentum lepton (use e’s), large bkg but still might be possible with enough data.

Some modes are very difficult at hadron colliders MC extrapolation to 50 ab  1 Observation of B ±  K ±  55 Super B LoI Fig.4.18 (compare to K +   + νν and K L   0 Extra EM calorimeter energy Belle result on B   ν shows that B to one prong decays can be measured. MC SM pred: G. Buchalla, G. Hiller, G. Isidori (PRD )

Conclusions on “Missing Energy Decays” Evidence for B   νand experimental determination of f B (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.

Backup Slides

Contributions to systematic error for B  

Peaking Backgrounds in B   Tau tagging mode

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

Requirements in B   ν analysis The  lepton is identified in the 5 decay modes. Signal selection criteria. Signal-side efficiency including  decay br.) All selection criteria were optimized before examining the signal region (blind analysis). 81% of all  decay modes  0.05%

Verification of the Signal (1) For events in the E ECL signal region, distribution of event selection variables other than E ECL are verified. They are consistent with MC expectation for B   signal + background. M bc P miss B   signal Background

Verification of the Signal(2) About 30% of background have neutral cluster in the KLM detector (K L candidates). The excess remains after requiring K L veto. We do not use this cut in the result, to avoid introducing a large systematic error due to the uncertainty in K L detection efficiency. K L in coincidence. K L in veto E ECL

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

γ K- π+π+ tagB Tag Side B  D + a1 - D +  K - π + π + a1 -  ρ 0 π -, ρ 0  π + π -