1. Semileptonic B decays in BaBar Cristiano Borean University and I.N.F.N. of Trieste on behalf of the BaBar Collaboration CIPANP 2003, New York

2. May 22 2003C. Borean CIPANP 20032 Semileptonic B decays Semileptonic decays are relatively simple theoretically at the parton level accessible experimentally sensitive to quark couplings to W ±, i.e. CKM elements |V cb | and |V ub | probe the dynamics of decays probe impact of strong interactions Two approaches Inclusive measurements: need OPE and b-quark mass to extract |V xb | from the total rate Exclusive measurements: need form-factors to describe the transition of the B meson to a lighter one

3. May 22 2003C. Borean CIPANP 20033 Inclusive Electrons with Electron Tags Analysis based on small sample: 4/fb on Y(4s), 1/fb off Y(4s) Data Selection Electron tag: p cms >1.4 GeV/c Electron signal: p cms > 0.6 GeV/c Electron ID: Combined likelihood based on: Electromagnetic Calorimeter (E/p, shower shape) DIRC (Cherenkov angle, # of photons) Driftchamber (dE/dx) Two signal samples: Right sign: + - Wrong sign: ++ or - -  e  (92.5  1.3) %

4. May 22 2003C. Borean CIPANP 20034 Electron Tagged Sample: Background Principal e  Backgrounds Conversion/Dalitz pairs Hadron mis-ID Continuum background Physics background Secondary e from other B: b  c  e + b   -  e -, b  c cs  e - Secondary e from same B charmonium B   e + e - B – B Mixing Secondary tag electrons  + - pairs from same B Cut: cos  +p* e >1.0 cos  >- 0.2 background P* e =0.75 GeV/c cos  >0.25

5. May 22 2003C. Borean CIPANP 20035 Right- and Wrong Sign Spectra Mixing  both spectra contain prompt and secondary e ± with  oa = Efficiency of cut on opening angle  : right-signwrong-sign  N prompt =25,070 (after correction for electron and tracking efficiency) right wrong

6. May 22 2003C. Borean CIPANP 20036 Fully Corrected Electron Spectrum Corrections of prompt spectrum: external bremsstrahlung 2.20 ± 0.35% geom. acceptance 84% single/di-lepton eff. 98% Total electron signal 25,070 ± 413 Total electron tags: 304,000 ± 880 ± 2100 Fit to sum of spectra from: B  D e, D * e, D ** e, D (*)  e B A B AR  Extrapolation to p = 0: correction: 6.1± 0.9%

7. May 22 2003C. Borean CIPANP 20037 Semileptonic Branching Ratio and |V cb | Integration over spectrum & extrapolation to p l *=0 : ARGUS : (9.7  0.5  0.4)% OPAL: (10.78  0.08  0.5)% CLEO2: (10.49  0.17  0.43)% L3: (10.89  0.20  0.51)% BELLE : (10.90  0.12  0.49)% ALEPH: (10.70  0.10  0.35)% Relation to |V cb | (A. Hoang, Z. Ligeti, A.V.Monahar) [1] : With  B =(1.6010.022)ps, and BR(B  X u e ) = (1.7  0.5) 10 -3 N.B. the theoretical errors have been added linearly BR(B  X e ) = (10.87  0.18 stat  0.30 sys )% | V cb | = 0.0423  0.0017 exp  0.0020 theory [1] Phys. Rev. Lett. 82 (1999) 591.

8. May 22 2003C. Borean CIPANP 20038 Exclusive mode: B 0 ->D*l Branching Fraction e/e/ D0D0 ss B Reconstruction of a charged D* meson and a lepton (either electron or muon) of opposite charge. Neutrino is NOT reconstructed. D 0 is reconstructed in 4 decay modes Constrained vertex fit on D 0 decay products, soft pion and lepton When possible study background from data control samples Used (85.9+/-0.9) x 10 6 Y(4s) decays

9. May 22 2003C. Borean CIPANP 20039 Classification of backgrounds D*lnuX bkg

10. May 22 2003C. Borean CIPANP 200310 Background Characterization: fit to  M [= M(D * )-M(D 0 )] fake D* fake lepton continuum uncorrelated from data control samples

11. May 22 2003C. Borean CIPANP 200311 Fit to the D*l X background B 0 ->D*l X events All shapes are extracted from MC e D 0  Kchannel Once other backgrounds are estimated from the global fit, B 0(+)  D * Xl events are separated using the angle between the B 0 and the D * l direction. Can be written as: D ** shape different from the D * one  fitted in 4 D 0 modes and e/m subsamples

12. May 22 2003C. Borean CIPANP 200312 Results and comparisons fit:  2 /d.o.f. = 21.3/23 B 0 ->D* - + )=( BR(B 0 ->D* - + )=(4.82±0.03 stat ±0.02 statMC ±0.24 exp ±0.17 BR )% preliminary Measurement limited by systematic uncertainties Main contributions to the experimental systematic error come from reconstruction efficiency and from the poor knowledge of the B  D*Xlnu background composition. Correlated measurements prel. BR aver =5.27 ± 0.29% C.L.= 6.4% Results rescaled to common inputs (f + /f 0 ).

13. May 22 2003C. Borean CIPANP 200313 Exclusive B 0 ->  e Analysis Used 50.5 1/fb on-resonance and 8.7 1/fb 40 MeV below Y(4s) resonance Study 5 modes B -> H u e where H u =  0,  , ,  0,   in 2 lepton energy ranges: LOLEP : 2.0 c e backgrounds) HILEP : 2.3 < E e < 2.7 GeV (large continuum backgrounds) Binned Likelihood fit with 2 variables:  E=E had + E lept + |p | - E beam, where |p | ~ |p miss |, and M had =  (  ) mass Take signal and backgrounds shapes from MC simulations, and continuum shape from off-peak data Extrapolate partial branching fraction to entire lepton- energy spectrum using 5 different form-factor calculations Determine |V ub | for each form-factor:

14. May 22 2003C. Borean CIPANP 200314 Fit projections for B 0 ->  - e + Continuum subtracted Isospin-constrained average of   and  0  2 = 91 (93 d.o.f.)

15. May 22 2003C. Borean CIPANP 200315 Branching Fraction and |V ub | results Theoretical error on the combined result: half of the full spread seen between the different form-factors Combined result: weighted average of 5 form-factor results. Theoretical error on combined result: half of the full spread seen between the FFs (including theoretical errors)

16. May 22 2003C. Borean CIPANP 200316 |V ub | from Inclusive Semil. Decays with Recoil Techinque Brecoil Breco D*  Y(4S) l XuXu Reco side Y(4s) D*  Recoil side Y(4s) Xu Subtract combinatorial bkg Breco (recoil) kinematics know with small uncertainties Breco (recoil) flavor Breco (recoil) charge (B 0 - B + separation) ~10 -3 efficiency: “small” efficiency l M X reconstruction Lepton charge – Breco (recoil) flavor correlation Kinematic constraints to improve M X resolution Partially reconstructed missing mass (soft pion) BB missing mass squared energy substituted mass

17. May 22 2003C. Borean CIPANP 200317 Analysis Method generated reconstructed Fully reconstruct one B B recoil selection and reconstruction of the X system B  X u l  One and only one lepton with p*> 1 GeV/c Correlation between lepton charge and B reco flavor (B 0 mixing is corrected) Cut on the missing mass: M miss 2 < 0.5GeV 2, charge conservation: Q tot =0 Partially reconstructed neutrino to reject B 0  D* l events kinematic fit (2-C): improve hadronic mass resolution Separate B  X u l in signal enriched and depleted: signal enriched: veto on K ± and K S used to perform the measurement signal depleted : one or more K ± or K S in the event used as control sample Systematics reduced by measuring R u/sl =B(B  X u l  )/B(B  X l  )

18. May 22 2003C. Borean CIPANP 200318 Extraction of B(b->ul ) Fit on the signal enhanced sample b  ul b  cl background Three components to fit the M X distribution: b  ul, b  cl, background Signal efficiency (  sel u  Mx u ), B reco efficiency ratio (  t u /  t sl ) and lepton efficiency ratio (  l u /  l sl  from MC Then multiply by B(B  Xl ) measured by BaBar

19. May 22 2003C. Borean CIPANP 200319 Result (82 fb -1 at the Y(4s) mass )

20. May 22 2003C. Borean CIPANP 200320 |V ub | result ( using ) We measured the charmless semileptonic branching ratio and we extracted |V ub |(*10 -3 ) BaBar Excl. B   e  3.29  0.42 stat  0.47 syst  0.60 theo BaBar Incl. electron spectrum endpoint  **  4.43  0.29 stat  0.25 exp  0.50 fu  035 s  BaBar Incl. Mx spectrum on the recoil 4.52  0.31 exp  0.27 syst  0.40 theo  0.24 pert  0.09 1/mb3 Inclusive |V ub | measurements (**) see hep-ex/0207081

21. May 22 2003C. Borean CIPANP 200321 Summary Result presented on Br(B->Xe ) and |V cb | with inclusive technique Physical Review D - Rapid Communications Year 2003 Volumn 67 Article/Page 031101 New measurement of Br(B 0 ->D*l ) Exclusive |V cb | mesurement with HQET zero-recoil is underway Exclusive |V ub | from B 0 ->  e : submitted to PRL New Inclusive |V ub | measurement: submitted to PRL

22. May 22 2003C. Borean CIPANP 200322 Backup Slides

23. May 22 2003C. Borean CIPANP 200323 The BaBar detector Cerenkov Detector Cerenkov Detector (DIRC) 144 quartz bars 11000 PMTs 1.5 T Solenoid Electromagnetic Calorimeter 6580 CsI(Tl) crystals Drift Chamber 40 stereo layers Instrumented Flux Return iron / RPCs (muon / neutral hadrons) Silicon Vertex Tracker 5 layers, double sided strips e + (3.1 GeV) e - (9 GeV) SVT: 97% efficiency, 15  m z hit resolution (inner layers, perp. tracks) SVT+DCH:  (p T )/p T = 0.13 %  p T + 0.45 % DIRC: K-  separation 4.2  @ 3.0 GeV/c  >3.0  @ 4.0 GeV/c EMC:  E /E = 2.3 %  E -1/4  1.9 %

24. May 22 2003C. Borean CIPANP 200324 Inclusive |V cb |: systematics

25. May 22 2003C. Borean CIPANP 200325 B 0 ->D*l Branching Fraction: Systematics

26. May 22 2003C. Borean CIPANP 200326 Br(B0->  - e + ): systematics

27. May 22 2003C. Borean CIPANP 200327 Inclusive |V ub |: systematics Statistical error (data+MC) 13.7% Detector simulation errors + Fit systematics 9.8% b  cl and D decays modeling + b  ul decays modeling 6.0% Fermi motion 17.5%