B at B-factories Guglielmo De Nardo Universita’ and INFN Napoli (on behalf of the BaBar collaboration)
Motivation Leptonic B decays in SM allow measurement of fB|Vub| Helicity suppressed, rare decay. SM prediction: (0.8 1.4)10-4 using exclusive or inclusive |Vub| values and fB=189 MeV Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
New Physics probe Additional tree level contribution from a charged Higgs It is not helicity suppressed . Then it may be competitive For example, in a MSSM model with 2 Higgs doublets From G.Isidori hep-ph/0605012 Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Tag side reconstruction p e+ Breco Brecoil e,,,,a1 1 or 2 Full reconstruction of a tag B hadronic D(*) X semileptonic D(*) l Search for evidence of In the rest of the event (recoil B) 20 4o 60 80 100 Branching Fraction ( % ) Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Signal side selection Signal kinematics and topology exploited with requirements on Particle identification, missing momentum, intermediate resonance mass ( 0, a1 ) The most discriminating variable is the remaining energy of what is left un-assigned. For signal events extra energy is expected to be zero Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Belle analysis ( 447 106 B pairs )
Hadronic tags 180 hadronic decay channels for tag B From known beam energies Constraint on the energy of the B The energy constrained mass fitted to get the number of tag B. N=680 K Eff=0.29% Purity =55% defines a signal region for the tag B -0.08 GeV < DE < 0.06 GeV, Mbc > 5.27 GeV/c2 ~10% systematic uncertainty in ntag Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Extra energy simulation The simulation has been check on a control sample of “double tag” events Btag hadronic, Bsig D(*) l B+B- 494 18 B0B0 7.9 2.2 Total 502 18 Data 458 Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Fitted signal yield Fit model parameters determined from MC simulation Background model 2nd order polynomial Gaussian peaking bg Signal model Gaussian with zero mean exponential signal events on a sample of 54 events ( 3.5 ) Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Detailed break-down and result Including the efficiencies in table and tag = 0.136% hep-ex/0604018 to appear in PRL using HFAG Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
mH vs tan limits Assuming the SM contributions to the BR from fB and |Vub|. Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
BaBar analysis ( 324106 B pairs )
Semileptonic tag B Reconstruct one tag B using semileptonic decays (B momentum from the beam) tag = (6.77 0.05 0.10) 10-3 Higher yields but less clean than hadronic tags 2% systematic uncertainty on tag B yield Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Extra energy simulation Simulation of the extra energy validated with a “double tag” control sample Fully reconstruct two semileptonic events and look at what is left unassigned Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Signal yield Background shape from MC simulation. sideband Events/0.1 GeV Background shape from MC simulation. Background yield in the signal region projected from the data sideband Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Results Cut and count method to extract the signal Likelihood composing poissonian probabilities Result consistent with no signal at 1.3 hep-ex/0608019 Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Results Calculated the upper limit at 90%CL using a modified frequentist method A. L. Read, J. Phys. G28, 2693 (2002) Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
mH vs tan exclusion plot BaBar+Belle (excluded at 95%CL) LEP, Direct Search (excluded at 95%CL) S.Sekula Assuming UT-fit value for BFSM ( B ) = (0.85 0.13)10-4 Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Conclusions Belle finds a signal of B decays at 3.5 level with a sample of 447 106 B pairs. analysis on the recoil of a fully reconstructed B in hadronic decay modes BaBar signal less strong. Lower central value With a sample of 324 106 B pairs Analysis on the recoil of a B D(*)l X decays Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006
Conclusions Belle central value is almost excluded by BaBar upper limit, but two results still consistent. In medio stat virtus. With more data the two results have to regress to the mean. Will we be able to see signal of NP in B ? The task is hard because we’d like be sensitive to a small deviation (downward) of a small signal BaBar is currently up-dating both the semileptonic tag and the hadronic tag analyses to the full data set An analysis with semileptonic tag from Belle would also help to compare results / increase the statistics Guglielmo De Nardo, CKM Workshop, Nagoya, Nov 12-16 2006