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Semileptonic and EW Penguin Decay Results from BaBar

Semileptonic and EW Penguin Decay Results from BaBar. I) Exclusive charmless SL decays Tagged analysis: B 0  p - l + n and B +  p 0 l + n Untagged analysis: B 0  p - (r - ) l + n Motivations: extract Vub (CKM) Form Factor calculations (QCD) II) B X s g decays

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Semileptonic and EW Penguin Decay Results from BaBar

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  1. Semileptonic and EW Penguin Decay Results from BaBar • I) Exclusive charmless SL decays • Tagged analysis: B0p-l+n and B+p0l+n • Untagged analysis: B0p-(r-)l+n • Motivations: • extract Vub (CKM) • Form Factor calculations (QCD) • II) BXsg decays • Fully inclusive analysis • Sum of exclusive states analysis • Motivations: • search for New Physics (NP) • photon spectrum in bsg decays is used to determine Heavy Quark parameters mb and mp2 (QCD) John J. Walsh INFN-Pisa BaBar Collaboration All results presented here are preliminary! XXXXth Rencontres de Moriond QCD and Hadronic Interactions La Thuile, Italy March 12-March 19, 2005

  2. Exclusive Bp(r)ln decays • |Vub| determines one side of the Unitarity Triangle • Precise measurments of |Vub| and sin2b constrain the U.T. • Error on |Vub| dominated by theory: • Inclusive analyses – prediction of spectra: theory error ~ 10-15% of |Vub|, need Shape Function from BXsg • Exclusive decays – theory must predict form factors – uncertainty hard to quantify • This talk  focus on new results from BaBar on exclusive decays Bp(r)ln : 2 types of analyses • Tagged analysis, using BD(*)ln of “other” B to tag event  reduced BG levels • Untagged analysis, emphasis on neutrino reconstruction  higher statistics Walsh - Moriond QCD 2005

  3. ISGW2 Ball’04 FNAL’04 HPQCD’04 Form Factors Bpln • Calculations: • Light-Cone Sum Rules • Ball/Zwicky (hep-ph/0406232) quote 10-13% uncertainty at q2=0 • Range of validity: q2 < 14 GeV2 • Lattice QCD • Unquenched calculations from HPQCD (hep-lat/0408019) and FNAL (hep-lat/0409116) quote 11% uncertainty at high q2 • Valid above ~ 15 GeV2 • ISGW2 • quark model Walsh - Moriond QCD 2005

  4. l D(*) v tag B signal B v p l Exclusive Bpln decays: tagged analysis • Use BD(*)ln decays of opposite B to “tag” event • consider only products of “recoil”  reduce combinatorial background • Use doubly-tagged BD(*)ln events to check tagging efficiency • Measure DB(B0p-l+n) in bins of q2 • BF for B+p0l+n Discriminating Variables • B0p-l+n: angle between the B momentum and the plane defined by the D(*)l and pl momenta: cos2fB • <~ 1 for signal events • flat distribution for BG • B+p0l+n: angle between B and p0l system: cos B-pl • Signal region: −1.1 < cosB-pl < 1.0 • BG much broader Walsh - Moriond QCD 2005

  5. Results: Tagged Analyses B0p-l+n 232 million BB pairs on-peak datasignal MCBrlv MCb ¨ ulv MCB0B0 MCB+B− MCoff-peak data 88 million BB pairs B+p0l+n Branching Fraction Results in 3 bins of q2 Walsh - Moriond QCD 2005

  6. Bp(r)ln: untagged analysis • Reconstruct neutrino from full event + ensure good reconstruction quality • Fit signal and background in DE, mES, and q2 q2 resolution neutrino momentum scaled so DE=0  improved q2 resolution Walsh - Moriond QCD 2005

  7. Data Signal MC Comb. Sig. Crossfeed bcln qq BABAR preliminary Bp(r)ln: Signal Extraction Bpln Brln Branching Fraction Results 83 million BB pairs Walsh - Moriond QCD 2005

  8. Form Factor Fits & |Vub| Untagged pln rln • The pln untagged sample begins to distinguish among FF calculations: ISGW II is disfavored: Prob(c2) = 3% • Other calculations tested are compatible with data Tagged Extraction of |Vub| (stat  syst  FFshapeFFnorm) BABAR preliminary uses LQCD-FNAL FF calculation Walsh - Moriond QCD 2005

  9. BXsg Measurements • Sensitive to New Physics • New heavy particles (Higgs, Susy) can participate in loop process • Hadronic Effects • Photon Spectrum can be used to measure Heavy Quark parameters • measure BR and moments as function of min Eg cut • largest uncertainty in |Vub| from inclusive buln decays due to b quark motion: can measure it with bsg • Two main experimental techniques: • fully inclusive • sum of exclusive modes b motion Emin Walsh - Moriond QCD 2005

  10. g B+ B- Xs e or m Xc n g B+ B- Kpp, Ksp, etc X bsg: Experimental Issues Fully Inclusive • Reconstruct high-energy photon (1.8-2.8 GeV) • Suppress huge background with lepton tagging • Main systematic from subtraction of BB background • Subtract bdg (~4%) Sum of Exclusive Modes • Sum of 38 modes: Knp, n=1-4, plus modes with h and 3 kaon modes • Kinematic constraints of fully-reconstructed B meson effectively reduces background • Photon energy measured directly in B rest frame  superior resolution • Primary systematic from missing modes (fragmentation) Walsh - Moriond QCD 2005

  11. Fully Inclusive bsg 89 million BB pairs Background-subtracted Event Yield • Continuum Background - • Lepton tagging • Event-shape cuts • Remaining removed using off-peak data subtraction • BB Background – • 80% from p0, h decays • explicit p0/h vetoes • Remaining subtracted using MC simulation – with corrections based on p0, h control sample Event yield in range 2.0 – 2.7 GeV: • Signal: 992  79stat  53BBsyst • BB BG: 675  53stat+syst • Cont. BG: 442  59 Walsh - Moriond QCD 2005

  12. Inclusive bsg: Partial BFs, 1st Moments Photon Energy Spectrum efficiency corrected • First step towards determination of HQ parameters, Shape Function • Coming soon: 2nd moment measurement • Further interaction with theory community to extract HQ parameters ( ± stat ± syst ± model ) BABAR preliminary Walsh - Moriond QCD 2005

  13. bsg: Sum of Exclusive States BABAR preliminary • Reconstruct 38 exclusive states containing K’s, p’s, h’s, etc.missing fraction is fcn of MXs • Usual B decay kinematic variables to extract signal: DE and mES • Very good photon energy resolution: note the K*g peak Energy-substituted Mass 89 million BB pairs Photon Energy Spectrum Walsh - Moriond QCD 2005

  14. ( ± stat ± syst ± model ) World Average (HFAG, August 2004) bsg (Semi-inclusive):BF and Spectrum Moments Good agreement with inclusive analysis Total BF for Eg>1.6 GeV, use average of Kinetic and Shape Fcn scheme results Values of moments  (For reference, do not try to read) Walsh - Moriond QCD 2005

  15. Scheme • Kinetic scheme results can be compared with inclusive SL result from BaBar: PRL 93, 011803 (2004) Kinetic ShapeFcn bsg (Semi-inclusive):Results on Heavy Quark Parameters BABAR preliminary • Heavy Quark parameters related to b-quark mass and its Fermi momentum inside the B-hadron: • Results derived for two different theoretical schemes: • Kinetic Scheme (Benson, Bigi, Uraltsev: hep-ph/0410080) • Shape Fcn Scheme (Neubert: hep-ph/0412241) OPE theory errors not included ( ± stat ± syst ± model ) Walsh - Moriond QCD 2005

  16. Summary • Preliminary results from BaBar on semileptonic and EW penguin decays • Exclusive analyses of Bp(r)ln using tagged and untagged samples: • Determination of |Vub| • BF measurements as function of q2 • Begin to test Form Factor calculations • The process bsgstudied with 2 experimental techniques: • fully inclusive: partial branching fractions and first moment as a function of Emin  towards HQ parameters • semi-inclusive: BF and moments (1-3)determination of mb and mp2 • Will give significant improvement in determination of |Vub| from inclusive SL measurements Walsh - Moriond QCD 2005

  17. Backup slides Walsh - Moriond QCD 2005

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