1 Semileptonic B Decays at BABAR Beauty 2005 Assisi (Perugia), June 20–24, 2005 Vladimir Golubev Budker Institute of Nuclear Physics, Novosibirsk, Russia (for the BaBar Collaboration)

V.Golubev - BABARBeauty2005, Assisi2 Semileptonic B Decays – Why are they Interesting Semileptonic decays theoretically simple at parton level rate depends on CKM elements |V cb | and |V ub |, the quark masses m b and m c the leptonic current factors out cleanly, thus one can probe strong interactions in B mesons sensitive to QCD corrections, OPE A precise determination of |V cb | and |V ub | with reliable errors important for understanding B decay rates testing of the unitarity of the CKM matrix and predictions of CP violation in B mesons +

V.Golubev - BABARBeauty2005, Assisi3 Semileptonic B decay studies at BABAR Inclusive decaysExclusive decay modes b  c l B  X c l |V cb |, total decay rate, HQE parameters B  D* l  B  D l  Branching fractions, decay form factors, |V cb | b  u l B  X u l |V ub |, total decay rate, lepton momentum and hadron mass spectra B   l  B    l  Branching fractions, decay form factors, |V ub | 2-nd B tagging: untagged, lepton tag, hadronic tag

V.Golubev - BABARBeauty2005, Assisi4 Inclusive B  X c l decays: HQE Expansions Heavy Quark Expansions, tool to correct for QCD effects Expansion in terms of 1/m b and  s (m b ) Separate short- and long-distance effects at  ~ 1 GeV Perturbative corrections calculable from m b m c  s (m b ) Non-perturbative parameters cannot be calculated We choose calculation by Gambino & Uraltsev hep-ph/ & Kinetic mass scheme to E ℓ moments m X moments 8 parameters to be fitted Measure 8 moments, each as a function of minimum lepton energy E l kinetic chromomagnetic Darwin spin-orbit

V.Golubev - BABARBeauty2005, Assisi5 Measurement of Electron Energy Moments Inclusive e ± spectrum in 3x10 6 electron- tagged (1.4<p*<2.3GeV/c) BB events Corrected for detector effects Corrected for non-prompt electrons – lepton charge correlation and MC Corrected for B 0 – B 0 mixing Moments for E cut = 0.6 … 1.5 GeV Corrected for the final state radiation Translated to B rest frame Subtracted B  X u ℓ  decays BABAR Partial BF Lepton Energy Moments /fb 156,000 e ± Albert et al. Phys.Rev. D 69, (2004)

V.Golubev - BABARBeauty2005, Assisi6 high mass charm states M x 2 [GeV 2 /c 4 ] Measurement of Hadron Mass Moments BB events tagged by a fully reconstructed hadronic B decays e ± or  ± with E l > E cut (0.9…1.6 GeV/c) Lepton charge – B flavor correlation Improve m x measurement by kinematic fit to whole event, resolution ~350 MeV To eliminate dependence of moments on uncertain BF and unknown masses of high mass charm mesons we calibrate m x measurement Calibrate m x based on MC simulation Linear relation between m x meas and m X true Validate calibration with excl. B  D (*) l Moments corrected for detector effects and bkg BABAR Hadron mass moments 7114 Events D, D* m x meas (Gev) m X true (GeV) Events/0.5 GeV 2 m X 2 (GeV 2 ) Aubert et al. Phys.Rev. D 69, (2004)

V.Golubev - BABARBeauty2005, Assisi7 HQE Fits to Hadron Mass and Lepton Energy Moments M X moments E ℓ moments ● = used, ○ = unused in the nominal fit Red line: HQE fit Yellow band: theory errors B A B AR   2 /ndf = 20/15 M1xM1x M2xM2x M3xM3x M4xM4x M0lM0l M1lM1l M2lM2l M3lM3l Aubert et al. Phys.Rev.Lett. 93, (2004)

V.Golubev - BABARBeauty2005, Assisi8 HQE Fit Results (kinetic mass scheme, scale  =1GeV)  Separate fits to hadron and lepton moments give consistent results   G 2 and  LS 3 are consistent with B-B* mass splitting and HQ sum rules  Considerable improvement in precision for |V cb | (±2%) and B c l   1.6%) and quark masses, as well as HQE parameters B A B AR

V.Golubev - BABARBeauty2005, Assisi9 |Vub| from total B  X u l decay rate Total b  u ℓ decay rate from OPE: |V ub | from inclusive BF(B  X u l ) (theory error  5%): Experimentally challenging due to charmed semileptonic background:

V.Golubev - BABARBeauty2005, Assisi10 |V ub | from partial B  X u l decay rates Charmed semileptonic background can be controlled in limited regions of phase space Non-perturbative Shape Functions are used to extract |V ub | from partial branching fractions. The SF parameters are extracted from b  sg photon spectrum New approach to |V ub | extraction: Differential decay rate parametrization from BLNP Bosch, Lange, Neubert, and Paz, Nucl. Phys. B 699, 335 (2004); Lange, Neubert, and Paz, hep-ph/ New source of information on SF parameters – moments of the b  c ℓ lepton spectrum Neubert, Phys.Lett. B 612, 13 (2005)

V.Golubev - BABARBeauty2005, Assisi11 |V ub | from partial B  X u l decay rates Different types of partial decay rate measurements: - electron endpoint - E e and q 2 regions with neutrino reconstruction - M x and q 2 regions hep-ex/ hep-ex/ hep-ex/ q 2 (Gev/c) 2 vs. M x (GeV)q 2 (Gev/c) 2 vs. E e (GeV) Kinematic regions of B  X c l decays q 2 =(p l +p ) 2

V.Golubev - BABARBeauty2005, Assisi12 (On-peak)-(Off-peak) data Histogram – B  X u l MC |V ub | from B  X u l endpoint spectrum Signal extraction: subtraction of BB and continuum background Differential  X u  e  branching fraction as a function of electron momentum, corrected for detector effects and final-state radiation (On-peak)−(Off-peak) data Histogram – B  X u l MC On-peak data Off-peak data (On-peak)-(Off-peak) data Histogram – B  X c l MC

V.Golubev - BABARBeauty2005, Assisi13 Determination of  Br for p e >p min Extrapolation to total charmless semileptonic decay Br using shape function parameters from B  X s  spectrum and calculations of DeFazio-Neubert ( * ) and Kagan-Neubert ( ** ) Extraction of |V ub | using the OPE relation. BABAR preliminary results, based on BELLE shape function parameters and DFN approach (hep-ex/ ):  Br(p e >2.0GeV/c)=(0.531  stat  syst )×10 -3 Br=(2.16  0.24 exp  0.27 SF )×10 -3 |V ub |=(4.40  0.24 exp  0.28 SF  0.21 OPE+mb )×10 −3 Analysis based on BLNP calculation is being completed ( * ) F.De Fazio and M.Neubert, JHEP 9906, 017 (1999) ( ** ) A.L.Kagan and M.Neubert, Eur.Phys.J. C 7, 5 (1999) Endpoint spectrum analysis: |Vub| extraction

V.Golubev - BABARBeauty2005, Assisi14 q 2 − E e analysis with neutrino reconstruction Event selection: High energy electron Ee>2GeV Missing momentum used for neutrino parameters estimation Cuts on missing momentum magnitude and direction, and event shape Suppression of b  ce by  s h max =m 2 D : (slightly modified for B -meson motion in the  (4S) rest frame) Acceptance ~ 14%, signal/bkg.~0.6

V.Golubev - BABARBeauty2005, Assisi15  Br(E e >2.0GeV, s h <3.5GeV 2 )=(3.54±0.33  ±0.34  q 2 − E e analysis results Test of neutrino energy resolution using pure control sample of B  D (*) e events Signal extraction for E e >2.0 GeV and s h <3.5 GeV 2, BB background normalization for s h >4.25 GeV 2, (*) B.O.Lange, M.Neubert and G.Paz, hep-ph/ B A B A R preliminary

V.Golubev - BABARBeauty2005, Assisi16 M x −q 2 analysis Select events with a fully reconstructed B  D ( * ) X decay (B reco ) Study charmless semileptonic decay of B recoiling against B reco - require lepton with p* lep > 1 GeV 2D fit to measure partial BF in [M x 8 GeV 2 ] Signal downfeed b  cl + other Mx < 1.7 GeV1.7 < Mx < 2.2 GeV2.2 < Mx < 2.8 GeV 82 fb -1 hep-ex/

V.Golubev - BABARBeauty2005, Assisi17 M x spectrum unfolding and fitting: M x −q 2 2-dimentional fit: M x −q 2 analysis: the results (*) F.De Fazio and M.Neubert, JHEP 9906, 017 (1999) (**) Bauer, Ligeti and Luke, hep-ph/ B A B A R preliminary (CKM 2005)

V.Golubev - BABARBeauty2005, Assisi18 Inclusive B  X u l decay summary Technique |V ub |×10 3 E l >2GeV (ICHEP2004) E l vs. q 2 (NEW) Mx vs. q 2 (CKM 2005) Average (using the procedure of HFAG) B A B A R preliminary

V.Golubev - BABARBeauty2005, Assisi19 HPQCD’04 Ball’04 FNAL’04 ISGW2 |Vub| from exclusive B  X u l decays q 2 = (p lep + p  ) 2 Strong nonperturbative effects included in form factors Calculations Light-Cone Sum Rules: Ball,Zwicky (hep-ph/ ) Unquenched Lattice QCD: HPQCD (hep-lat/ ) and FNAL (hep-lat/ ) ISGW2: quark model

V.Golubev - BABARBeauty2005, Assisi20 Exclusive decays, experimental techniques Different experimental approaches to measure BF: Untagged analysis Semileptonic Tags Hadronic Tags Neutrino reconstruction B  ℓ, B  ℓ Recoil of B  D ( * ) ℓ B  ℓ Recoil of B  D ( * ) X 9 channels ( , , , ,  ’,a 0 ) PURITY EFFICIENCY

V.Golubev - BABARBeauty2005, Assisi21 Exclusive B   l decays, tagged analysis l l D (*) v v  signal B tag B Use B  D (*) l decays of opposite B to “tag” event Use events with B  D (*) l decays on both sides to check tagging efficiency Measure  B(B 0   - l + ) in bins of q 2 BF for B +   0 l + Discriminating Variables B 0   - l + angle between the B momentum and the plane defined by the D (*) l and  l momenta: cos 2  B B +   0 l + angle between B and  0 l system: cos  B-  l

V.Golubev - BABARBeauty2005, Assisi22 B   l tagged analysis: the results on-peak data signal MC B   lv MC b  ¨ ulv MC B 0 B 0 MC B + B − MC off-peak data 232 million BB pairs 88 million BB pairs B 0   - l + B +   0 l + Branching Fraction Results in 3 bins of q 2 B A B A R preliminary (CKM 2005)

V.Golubev - BABARBeauty2005, Assisi23 Exclusive B   l decays, untagged analysis Reconstruct neutrino from full event + ensure good reconstruction quality Signal yield extracted from common fit to  E and m ES in 5 q 2 bins for  + l and 3 bins for   l and   l each neutrino momentum scaled so  E=0  improved q 2 resolution q 2 resolution

V.Golubev - BABARBeauty2005, Assisi24 Untagged B   l signal extraction Data Signal MC Comb. Sig. Crossfeed b  cl qq B   l + B  l 83 million BB pairs B A B A R preliminary Branching Fraction Results

V.Golubev - BABARBeauty2005, Assisi25 The  l untagged sample begins to distinguish among FF calculations: ISGW II is disfavored: Prob(  2 ) = 3% Other FF calculations tested are compatible with data Form factor fits and |V ub | extraction Untagged  l  l B A B A R preliminary (CKM 2005) Extraction of |V ub |

V.Golubev - BABARBeauty2005, Assisi26  HQE fits to moments hadronic mass and lepton energy moments: Based on 80 fb -1, ~30% of the current BABAR data, we have made significant advances in the analysis of semileptonic B decays. Br(B  X c l )= (10.61 ±0.16 exp ±0.06 HQE )% High precision measurement of m b and m c, and exp. determination of HQE parameters.  Inclusive B  X u l decays, three different approaches: The most precise determination of |V ub | Measurement of partial semileptonic branching fractions for different kinematic regions  Exclusive B   (  ) l decay modes in tagged and untagged samples: Determination of |V ub | Begin to test decay form factor calculations The analyses will be repeated for larger data samples and more precise shape function parameters derived from from B  X s  photon spectrum Summary