Semileptonic B Decays at BABAR Vladimir Golubev Budker

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

Semileptonic B Decays – Why are they Interesting + n Semileptonic decays n n n theoretically simple at parton level rate depends on CKM elements |Vcb| and |Vub|, the quark masses mb and mc the leptonic current factors out cleanly, thus one can probe strong interactions in B mesons n n sensitive to QCD corrections, OPE A precise determination of |Vcb| and |Vub| with reliable errors important for n n understanding B decay rates testing of the unitarity of the CKM matrix and predictions of CP violation in B mesons V. Golubev - BABAR Beauty 2005, Assisi 2

Semileptonic B decay studies at BABAR Inclusive decays b c ln b u ln Exclusive decay modes B Xc l B D* l , B D l , . . . |Vcb|, total decay rate, HQE parameters Branching fractions, decay form factors, |Vcb| B Xu l B l , . . . |Vub|, total decay rate, lepton momentum and hadron mass spectra Branching fractions, decay form factors, |Vub| 2 -nd B tagging: untagged, lepton tag, hadronic tag V. Golubev - BABAR Beauty 2005, Assisi 3

Inclusive B Xc l decays: HQE Expansions n Heavy Quark Expansions, tool to correct for QCD effects n n n We choose calculation by Gambino & Uraltsev n n Expansion in terms of 1/mb and as(mb) Separate short- and long-distance effects at m ~ 1 Ge. V n Perturbative corrections calculable from mb mc as(mb) n Non-perturbative parameters cannot be calculated Kinetic mass scheme to Eℓ moments m. X moments 8 parameters to be fitted hep-ph/0401063 & 0403166 kinetic chromomagnetic spin-orbit Darwin n Measure 8 moments, each as a function of minimum lepton energy El V. Golubev - BABAR Beauty 2005, Assisi 4

Measurement of Electron Energy Moments BABAR Albert et al. Phys. Rev. D 69, 111104 (2004) 47 + 9 /fb n Inclusive e± spectrum in 3 x 106 electrontagged (1. 4<p*<2. 3 Ge. V/c) BB events n n Corrected for detector effects Corrected for non-prompt electrons – lepton charge correlation and MC Corrected for B 0 – B 0 mixing 156, 000 e± Moments for Ecut = 0. 6 … 1. 5 Ge. V n n n Corrected for the final state radiation Translated to B rest frame Subtracted B Xuℓ decays Partial BF Lepton Energy Moments V. Golubev - BABAR Beauty 2005, Assisi 5

Measurement of Hadron Mass Moments BB events tagged by a fully reconstructed hadronic B decays n n n To eliminate dependence of moments on uncertain BF and unknown masses of high mass charm mesons we calibrate mx measurement Calibrate mx based on MC simulation n e± or m± with El > Ecut (0. 9… 1. 6 Ge. V/c) Lepton charge – B flavor correlation Improve mx measurement by kinematic fit to whole event, resolution ~350 Me. V Linear relation between mxmeas and m. Xtrue Validate calibration with excl. B D(*) l Moments corrected for detector effects and bkg BABAR 7114 Events D, D* high mass charm states m. X 2 (Ge. V 2) Mx 2[Ge. V 2/c 4] mxmeas (Gev) n Events/0. 5 Ge. V 2 Aubert et al. Phys. Rev. D 69, 111103 (2004) Hadron mass moments V. Golubev - BABAR Beauty 2005, Assisi m. Xtrue (Ge. V) 6

HQE Fits to Hadron Mass and Lepton Energy Moments Aubert et al. Phys. Rev. Lett. 93, 011803 (2004) BABAR M 1 x MX moments M 2 x M 0 l c 2/ndf = 20/15 V. Golubev - BABAR ● = used, ○ = unused in the nominal fit M 1 l M 3 x M 4 x M 2 l M 3 l Red line: HQE fit Yellow band: theory errors Eℓ moments Beauty 2005, Assisi 7

HQE Fit Results (kinetic mass scheme, scale m=1 Ge. V) BABAR v Separate fits to hadron and lepton moments give consistent results v m. G 2 and r. LS 3 are consistent with B-B* mass splitting and HQ sum rules v Considerable improvement in precision for |Vcb| (± 2%) and Bcl (1. 6%) and quark masses, as well as HQE parameters V. Golubev - BABAR Beauty 2005, Assisi 8

|Vub| from total B Xu l decay rate n Total b u ℓ decay rate from OPE: n |Vub| from inclusive BF(B Xu l ) (theory error 5%): n Experimentally challenging due to charmed semileptonic background: V. Golubev - BABAR Beauty 2005, Assisi 9

|Vub| from partial B Xu l decay rates n n n Charmed semileptonic background can be controlled in limited regions of phase space Non-perturbative Shape Functions are used to extract |Vub| from partial branching fractions. The SF parameters are extracted from b sg photon spectrum New approach to |Vub| extraction: • • Differential decay rate parametrization from BLNP Bosch, Lange, Neubert, and Paz, Nucl. Phys. B 699, 335 (2004); Lange, Neubert, and Paz, hep-ph/0504071 New source of information on SF parameters – moments of the b c ℓ n lepton spectrum Neubert, Phys. Lett. B 612, 13 (2005) V. Golubev - BABAR Beauty 2005, Assisi 10

|Vub| from partial B Xu l decay rates n Different types of partial decay rate measurements: - electron endpoint hep-ex/0408075 - Ee and q 2 regions with hep-ex/0506036 neutrino reconstruction - Mx and q 2 regions q 2(Gev/c)2 vs. Ee(Ge. V) hep-ex/0408068 q 2=(pl+p )2 q 2(Gev/c)2 vs. Mx(Ge. V) Kinematic regions of B Xcl decays V. Golubev - BABAR Beauty 2005, Assisi 11

|Vub| from B Xu l endpoint spectrum On-peak data Off-peak data (On-peak)-(Off-peak) data Histogram – B Xcl MC (On-peak)-(Off-peak) data Histogram – B Xul MC Differential B Xu e branching fraction as a function of electron momentum, corrected for detector effects and final-state radiation Signal extraction: subtraction of BB and continuum background V. Golubev - BABAR Beauty 2005, Assisi (On-peak)−(Off-peak) data Histogram – B Xul MC 12

Endpoint spectrum analysis: |Vub| extraction n n Determination of DBr for pe>pmin Extrapolation to total charmless semileptonic decay Br using shape function parameters from B Xsg spectrum and calculations of De. Fazio-Neubert(*) and Kagan-Neubert(**) Extraction of |Vub| using the OPE relation. BABAR preliminary results, based on BELLE shape function parameters and DFN approach (hep-ex/0408075): DBr(pe>2. 0 Ge. V/c)=(0. 531 0. 032 stat 0. 049 syst)× 10 -3 Br=(2. 16 0. 24 exp 0. 27 SF)× 10 -3 |Vub|=(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) V. Golubev - BABAR Beauty 2005, Assisi 13

q 2 − Ee analysis with neutrino reconstruction n n Event selection: High energy electron Ee>2 Ge. V Missing momentum used for neutrino parameters estimation Cuts on missing momentum magnitude and direction, and event shape Suppression of b cen by shmax=m 2 D: (slightly modified for B -meson motion in the U(4 S) rest frame) Acceptance ~ 14%, signal/bkg. ~0. 6 V. Golubev - BABAR Beauty 2005, Assisi 14

BABAR q 2 − Ee analysis results preliminary Test of neutrino energy resolution using pure control sample of B D(*)e events Signal extraction for Ee>2. 0 Ge. V and sh<3. 5 Ge. V 2, BB background normalization for sh>4. 25 Ge. V 2, DBr(Ee>2. 0 Ge. V, sh<3. 5 Ge. V 2)=(3. 54± 0. 33 ± 0. 34) ´ 10 -4 (*) V. Golubev - BABAR Beauty 2005, Assisi B. O. Lange, M. Neubert and G. Paz, hep-ph/0504071 15

Mx−q 2 analysis n Select events with a fully reconstructed B D(*)X decay (Breco) n Study charmless semileptonic decay of B recoiling against B reco - require lepton with p*lep > 1 Ge. V n 2 D fit to measure partial BF in [Mx<1. 7 Ge. V, q 2>8 Ge. V 2] Mx < 1. 7 Ge. V downfeed hep-ex/0408068 1. 7 < Mx < 2. 2 Ge. V Signal 2. 2 < Mx < 2. 8 Ge. V 82 fb-1 b cl + other V. Golubev - BABAR Beauty 2005, Assisi 16

Mx−q 2 analysis: the results BABAR preliminary (CKM 2005) n Mx spectrum unfolding and fitting: (*) F. De Fazio and M. Neubert, JHEP 9906, 017 (1999) Bauer, Ligeti and Luke, hep-ph/0111387 (**) n Mx−q 2 2 -dimentional fit: V. Golubev - BABAR Beauty 2005, Assisi 17

Inclusive B Xu l decay summary Technique BABAR preliminary |Vub|× 103 El>2 Ge. V (ICHEP 2004) El vs. q 2 (NEW) Mx vs. q 2 (CKM 2005) Average (using the procedure of HFAG) V. Golubev - BABAR Beauty 2005, Assisi 18

|Vub| from exclusive B Xu l decays Strong nonperturbative effects included in form factors q 2 = (plep + p )2 ISGW 2 Ball’ 04 FNAL’ 04 HPQCD’ 04 Calculations n n n Light-Cone Sum Rules: Ball, Zwicky (hep-ph/0406232) Unquenched Lattice QCD: HPQCD (hep-lat/0408019) and FNAL (hep-lat/0409116) ISGW 2: quark model V. Golubev - BABAR Beauty 2005, Assisi 19

Exclusive decays, experimental techniques n Different experimental approaches to measure BF: Untagged analysis Neutrino reconstruction B ℓ , B ℓ Semileptonic Tags Recoil of B D(*) ℓ n B ℓ Hadronic Tags Recoil of B D(*)X 9 channels (p, r, , , ’, a 0) V. Golubev - BABAR Beauty 2005, Assisi PURITY EFFICIENCY 20

Exclusive B l decays, tagged analysis v l D(*) tag B p n n signal B v l 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 DB(B 0 -l+ ) in bins of q 2 BF for B+ 0 l+ V. Golubev - BABAR n n Discriminating Variables B 0 p-l+n: angle between the B momentum and the plane defined by the D(*)l and l momenta: cos 2 f. B B+ p 0 l+n: angle between B and 0 l system: cos B-pl Beauty 2005, Assisi 21

B l tagged analysis: the results BABAR preliminary (CKM 2005) B 0 p-l+ 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 B+ p 0 l+ Branching Fraction Results in 3 bins of q 2 88 million BB pairs V. Golubev - BABAR Beauty 2005, Assisi 22

Exclusive B ( ) l decays, untagged analysis • • Reconstruct neutrino from full event + ensure good reconstruction quality Signal yield extracted from common fit to DE and m. ES in 5 q 2 bins for +l , and 3 bins for -l and 0 l each q 2 resolution neutrino momentum scaled so DE=0 improved q 2 resolution V. Golubev - BABAR Beauty 2005, Assisi 23

Untagged B ( ) l , signal extraction B -l+ B l BABAR preliminary Data Signal MC Comb. Sig. Crossfeed b cl qq Branching Fraction Results 83 million BB pairs V. Golubev - BABAR Beauty 2005, Assisi 24

BABAR Form factor fits and |Vub| extraction Untagged pln rln n n preliminary (CKM 2005) The l untagged sample begins to distinguish among FF calculations: ISGW II is disfavored: Prob(c 2) = 3% Other FF calculations tested are compatible with data Extraction of |Vub| V. Golubev - BABAR Beauty 2005, Assisi 25

Summary v 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 Xc l )= (10. 61 ± 0. 16 exp ± 0. 06 HQE)% High precision measurement of mb and mc, and exp. determination of HQE parameters. v Inclusive B Xu l decays, three different approaches: The most precise determination of |Vub| Measurement of partial semileptonic branching fractions for different kinematic regions v Exclusive B p(r) l decay modes in tagged and untagged samples: Determination of |Vub| Begin to test decay form factor calculations The analyses will be repeated for larger data samples and more precise shape function parameters derived from B Xsg photon spectrum V. Golubev - BABAR Beauty 2005, Assisi 26