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  1. L.ListaINFN Sezione di Napoli Results of BABAR experiment on CP violation and B physics Luca Lista

  2. Outline • Experimental set-up • Charmonium decays • B lifetime measurement • Mixing and CP asymmetry • Rare B decays • Future perspective and Conclusions (4S) Luca Lista

  3. center of mass energy  MU(4S) =10.58 GeV/c2 bg= 0.56 at Stanford Linear Accelerator Center (California) Low Energy Ring [e+, 3.1GeV] BaBar High Energy Ring [e-, 9.0GeV] Has delivered 23.7 fb-1 from Oct. 99 to Nov.2000 The PEP-II B-Factory Luca Lista

  4. Performance during the 99-00 run Luca Lista

  5. Electromagnetic Calorimeter 6580 CsI(Tl) crystals 1.5T solenoid e+ DIRC (PID) 144 quartz bars 11000 PMTs Drift Chamber 40 axial stereo layers e- Instrumented Flux Return 19 iron / 18-19 RPC layers Silicon Vertex Tracker 5 layers, 2-sided Si strips The BaBar detector Luca Lista

  6. The Silicon Vertex Tracker Beam bending magnets high radiation area Beam pipe layer 1,2 layer 3 layer 4 layer 5 • 5 layers: 20o< <150o; • R= 3.2, 4, 5.4, 9.1-12.7, 11.4-14.4 cm • Single hit resolution: 10-15 mm Luca Lista

  7. The Drift Chamber (pT)/pT= 0.13%  pT 0.45% • 40 axial and stereo layers for Z measurement • small hexagonal cells (11.9 x 19.0 mm) • 80%:20% helium:isobutane Luca Lista

  8. The Cherenkov detector (DIRC) • Internally reflected Cherenkov radiation • ~11000 phototubes Luca Lista

  9. The Electromagnetic Calorimeter • Identification of e±,g,p0 • Energy resolution: Luca Lista

  10. The Instrumented Flux Return Muon and KL reconstruction 18/19 RPC planes ~53000 electronic channels Luca Lista

  11. B-counting • The determination of B decays branching ratios requires a precise estimate of the number of produced (4S)BB events • Counting of Multi-Hadron events • Correction factor:  = 0.99620.0027 • Different efficiencies for mm and MH on and off-resonance • 22,700,000 BB events,1.7% sys. error Luca Lista

  12. b c Efficiency J/, (2S), c c W- B0, B- s, d X d, u Efficiency muons pions Inclusive Charmonium Decays • J/, (2S) and c are reconstructed in final states containing leptons • Different selection purity for different decays Luca Lista

  13. Inclusive J/ decays p*J/ < 2 GeV/c • Inclusive branching ratio: Br(BJ/X) = (1.0440.013 0.028)10-2 Br(BJ/X dir.) = (0.7890.010 0.034)10-2 • p*: J/ momentum distribution in the (4S) system • B system coincides with (4S) within 250 MeV J/ e+e- J/ +- Luca Lista

  14. J/ momentum spectrum BB events continuum Luca Lista

  15. J/ production in continuum • First observation of J/ production in continuum • BB events rejected by p*>2 GeV/c • Rejection of Initial State Radiation • Ntracks, Etot, R2 Angular distribution1+A cos2q* • A (all E*) = 0.250.19 • A (p*>3.5 GeV) l= 0.620.39 • Color singles prediction: A  –0.8,   0.8 pb • NRQCD (c.o.) prediction: 0.6<A<1.0,   2.8 pb Luca Lista

  16. Inclusive (2S) decays Br( B (2S) X ) = (0.2750.020 0.029) 10-2 (2S) l+l-, J/+- p* < 1.6 GeV/c • (2S)  l+l- branching ratio measurement • Assuming PDG values for (2S)J/+-: Luca Lista

  17. Inclusive c decays • Br(B c1 X) = ( 0.378  0.034  0.026 )  10-2 • Br(B c1 X dir.) = ( 0.353  0.034  0.024 )  10-2 • Br(B c2 X) < 0.2110-2 @ 90% C.L.= ( 0.137  0.058  0.012 )  10-2 c2 (?) c2 (?) Luca Lista

  18. Exclusive B decays • Motivation: • Several channels are used to constrain the unitarity triangle • Charged modes may exhibit direct CP asymmetry • Probe of non perturbative QCD • Theoretical prediction available for many decays in the factorization hypothesis • Kinematics selection: • Energy substituted mass • Independent on particle mass hypotheses • Energy difference in the center of mass Luca Lista

  19. Golden CP mode: BJ/K0S Luca Lista

  20. BJ/K0L • KL reconstructed as neutral deposit in the I.F.R. or E.M. Calorimeter • 1.4 < p*J/ < 2.0 GeV/c • No KL momentum measurement • DE is determined assuming the mBmass constraint Luca Lista

  21. Selected rare channels First observation: B0C1 K*0 B0J/ 0 Luca Lista

  22. Branching ratios results Luca Lista

  23. BaBar compared to PDG 2000 Luca Lista

  24. +1.9 ( 5.0  0.1 ) % -1.7 J/+ / J/K+ • Cabibbo and color suppressed tree diagram • possible CP asymmetry from penguin contribution • Unbinned maximum likelihood fit based on kinematical variables: Br(B+J/+)/Br(B+J/K +) =(3.910.78 0.19)10-2 ( 5.2  2.4 ) % ( 5.1  1.4 ) % Luca Lista

  25. Z e-e+ 9 GeV 3.1GeV Dz bg= 0.56 gbctB@260mm B± and B0/B0 lifetimes • One B is fully reconstructed • in a B0 or B mode • Measure both B vertices • Fit for Dt @ Dz/c gBU bgUlab • ideally PDF(Dt)  exp(-|Dt|/tB) • Novel method for • asymmetric e+e- machines • Different systematics from • previous measurements • Detailed understanding of • resolution function needed B1 partially reconstructed sz ~ 140mm B2 fully reconstructed sz~ 60-100 mm Luca Lista

  26. The 99-00 data sample 22.7 106 BB pairs recorded B0/B0 B B0  D(*)+  - D(*)+- D(*)+a1- J/K*0 B-  D(*)0  - J/K- (2S)K- 6967 ± 95 purity  90% 7266 ± 94 purity  93% Luca Lista

  27. Fitting procedure B0/B0 MC Resolution function fitted on data: R(Dt)=f*Gaus(s)+(1-f)*Gaus(s)Exp(k) identical for B±andB0/ B0 psig from mass distribution fit t residual/ t Unbinned maximum likelihood fit: Bkg description from side-band events Luca Lista

  28. B B0/B0 background Dt (ps) Dt (ps) preliminary Lifetime results t0 = 1.546  0.032(stat)  0.022(syst) ps t  = 1.673  0.032(stat)  0.022(syst) ps t0 /t = 1.082  0.026(stat)  0.011(syst) common resolution Luca Lista

  29. Other lifetime ratio measurements Luca Lista

  30. A=(,) B=(1,0) C=(0,0) The Unitarity Triangle • Unitarity relations on matrix elements lead to a triangle in the complex plane • Quark mixing is described by the CKM matrix    1 Luca Lista

  31. CP violation via mixing interference in bccs B0 J/yK0s B0 t d b B0 B0 W W t b d @Dt=0 B0 B0 F- F+ Dt(ps) CP violation at asymmetric B factory Integrated asymmetry = 0 time dependent analysis required • coherent production: • Y(4S)  BB •  clock starts at • 1st B decay Luca Lista

  32. J/K0S (p+p-) 425 ± 22 purity  94% J/K0S (p0p0) hCP = -1 (2S)K0S (p+p-) J/K0L hCP = +1 199 ± 23 purity  45% The 99-00 data sample: CP modes Luca Lista

  33. B01 partially reconstructed flavour tagged B02 fully reconstructed D*+  - or J/K0S e-e+ B1 = B0 B1 = B0 unmixed B0 B0 Dz mixed B0B0 or B0B0 Mixing and CP asymmetry of B0/B0 CP modes: FCP(Dt)  e-|Dt|/tB ( 1  hCP sin2b. sin Dmd Dt ) Flavour specific modes: Fflav(Dt)  e-|Dt|/tB ( 1  cos DmdDt ) Luca Lista

  34. leptons:b  l- , b  l+ • p*>1.0 GeV/c (e±), p*>1.1 GeV/c (m±) • e = 10.9  0.4% • kaons: b  K- , b  K+ • e = 36.5  0.7% Tagging the flavour of the B0CP/flav Look at the second B in the event • Neural network mainly to • recover unidentified leptons • and use soft pions from D* • NT1:e = 7.7  0.4% • NT2:e = 13.7  0.5% • Total e = 68.9  1.0% Luca Lista

  35. perfect tagging/ resolution imperfect tagging/ perfect resolution imperfect tagging/ imperfect resolution B0 B0 e-|Dt|/tB (1hCP sin2b  sin Dmd Dt) e-|Dt|/tB (1hCP Dsin2b sin Dmd Dt) e-|Dt|/tB (1hCP D sin2b  sin Dmd Dt)  R(Dt) unmixed mixed e-|Dt|/tB (1cos DmdDt) e-|Dt|/tB (1 D cos Dmd Dt) e-|Dt|/tB (1D cos DmdDt)  R(Dt) Imperfect tagging and resolution Luca Lista

  36. largest correlation withsin2b: 7.6% Fitting Procedure unbinned maximum likelihood fit: • Dmd : flavour specific sample • sin2b : flavour specific +CP samples Mainly constrained by high stat flavour sample Empirical description fitted on data Luca Lista

  37. Fraction of wrongly tagged events s(sin2b) 1/(Q) NT2 kaons NT1 leptons Flavour misid. measurement D = 1 - 2 w Check w with a time-integrated method (events with |Dt|<2.5 ps to optimise s(w)) On the same sample and on ~11000 D*ln Luca Lista

  38. Dmdmeasurement preliminary Dmd= 0.519 ±0.020stat±0.016systps-1 e-|Dt|/tB (1D cos DmdDt)  R(Dt) Luca Lista

  39. l+or l- e-e+ l+or l- N+–, –+ – N++, –– Asymmetry A(Dz)= N+ –, –+ + N++, –– Dz Dmdmeasurement: the di-lepton analysis Dmd= 0.499 ± 0.010 ± 0.012 ps-1 Luca Lista

  40. preliminary preliminary Luca Lista

  41. sin2b results sin2b=0.25±0.22stat sin2b=0.87±0.51stat sin2b = 0.34 ± 0.20stat ± 0.05syst Luca Lista

  42. Time dependent asymmetry hCP = -1 sin2b=0.25±0.22stat ln(L/Lmax) hCP = +1 sin2b sin2b=0.87±0.51stat combined result Luca Lista

  43. Cross-checks: sin2b on sub-samples sin2 sin2 Luca Lista

  44. sin2b systematic uncertainties Luca Lista

  45. World average for sin2b Luca Lista

  46. 1s 2s Unitarity triangle sin2b = 0.34 ± 0.20stat ± 0.05syst Luca Lista

  47. J/ K*0 angular analysis • L=0,1,2 waves • Both CP even and odd amplitudes are present • Measurement of sin2b is possible from angular analysis f (costr, cosK*, tr) = f1 |A0|2 + f2 |A|||2 + f3|A|2f4 Im(A||* A) + f5 Re (A0* A||) + f6 Im (A0* A) Channels withoutp0 Channels withp0 J/ rest frame K* decay plane |A|2 + |A|||2 + |A0|2 = 1 Luca Lista

  48. J/ K* angular analysis Indication of FSI (a) Raw measurement (b) Acceptance correction (c) “ “ + mES fit (d) “ “ + (Self) Feed Across Time dependent CP asymmetry dilution factor: D =1 – 2|A|2 = 0.680.10 Luca Lista

  49. B  D*D(*)K • Study of the bccs transition • Experimental inclusive estimate from from BDSX, (cc)X, CX, CX (ALEPH, CLEO) • Br(bccs) ~ 15.82.8 % • Theoretical calculation can’t determine this low value together with inclusive s.l. branching ratio (bcW) • Three-body B  DDK can contribute • Study of color suppressed modes (B+ D*+D*-K+) Color suppressed Color allowed Luca Lista

  50. B  D*D(*)K • Reconstructed decays: • D*+ D0p+ • D*0 D0p0 • D*0 D0g • D0 K-p+ • D0 K-p+p0 • D0 K-p+p-p+ • D+ K-p+p+ • Br(B0 D*+D0K+) = (0.280.070.05)10-2 • Br(B0 D*+D*0K+) = (0.680.170.17)10-2 • Br(B+ D*+D*-K+) = (0.340.160.11)10-2 • First observation of color suppressed mode other than B  (charmonium)X B0 (all modes) NS = 18021 B+ (all modes)NS = 11715 B+ D*+D*-K+ NS = 8.23.5 Luca Lista