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B 0 B 0 Oscillations and sin2 b at B A B A R

B 0 B 0 Oscillations and sin2 b at B A B A R. David Nathan Brown Lawrence Berkeley National Laboratory Representing the B A B A R Collaboration. Outline. B 0 B 0 mixing and CP in the Standard Model B A B A R and PEPII Event sample Analysis procedure Signal channel selection

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B 0 B 0 Oscillations and sin2 b at B A B A R

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  1. B0B0 Oscillations and sin2bat BABAR David Nathan Brown Lawrence Berkeley National Laboratory Representing the BABAR Collaboration David Nathan Brown 1Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  2. Outline • B0B0mixing and CP in the Standard Model • BABAR and PEPII • Event sample • Analysis procedure • Signal channel selection • Flavor tagging • Time measurement resolution modeling • Fitting • Results • DmB0 • sin2b • Systematic error estimation • Conclusions David Nathan Brown 2Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  3. Quark mixing in the Standard Model Quark electroweak doublets are composed of mass eigenstate mixtures given by a mixing matrix. Unitarity of the mixing matrix can be shown graphically as a triangle. Non-zero triangle area (a,b, or g != 0) implies CP violation A ‘triangle’ which doesn’t close implies non-SM physics David Nathan Brown 3Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  4. B0B0 mixing can proceed through EW box diagrams B0B0 Mixing DmB0is sensitive to |VtdVtb*| David Nathan Brown 4Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  5. CP Violation via Mixing Interference Interference between mixed and unmixed B0 decays to CP eigenstates induces a time and flavor-dependent rate B0 J/Y K0S B0 Flavor-specific rate vs time depends on sin2b David Nathan Brown 5Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  6. J/  + -  B0 p- bzg ~ 0.56 K0 (4S) B0 Dz ~250 mm CP and Mixing at the ¡(4S) ¡(4S) B0B0proceeds via coherent P-wave. Tagging the flavor of one B at decay determines the flavor of the other at that instant. Reco side By boosting the ¡(4S) the decay time difference becomes observable. Tagging side David Nathan Brown 6Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  7. PEPII at SLAC 3.1 GeV e+ ¡(4S) 9 GeV e- David Nathan Brown 7Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  8. The BaBar Detector Silicon Vertex Tracker (SVT) Superconducting Coil (1.5 Tesla) Drift Chamber (DCH) CsI Calorimeter (EMC) Instrumented Flux Return (IFR) Cherenkov Detector (DIRC) David Nathan Brown 8Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  9. The BaBar Data Sample 23 Million B0B0 pairs recorded David Nathan Brown 9Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  10. A Fully-Reconstructed ¡(4S)B0B0 Event David Nathan Brown 10Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  11. Event Reconstruction • ‘Stable’ particle reconstruction • Tracking • dE/dx and DIRC PID • Vertexing (ks,  • and m in EMC and IFR • Neutrals in EMC and IFR • ¡(4S) BBselection • Event shape cuts (FW, thrust) David Nathan Brown 11Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  12. J/Ks and Ks Reconstruction 363 Events above background David Nathan Brown 12Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  13. J/KL Reconstruction • KL are found in EMC and IFR • Cluster with no associated track • Inconsistent with p0 or g • B0 mass used to reconstruct candidates (no cut) EMC clusters IFR clusters 182 Events above background David Nathan Brown 13Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  14. Hadronic (non-CP) B0 Reconstruction • B0D(*)-(p,r,a1)+ • D-K-p+p+,K0p- • D0K-p+, K-p+ p0, K-p+p-p+, K0p-p+ • D*- D0p- • B0J/K*0 • K*0 K-p+ 4637 Events above background (CP fit) 6368 Events above background (DmB0 fit) David Nathan Brown 14Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  15. Flavor Tagging • Tags are assigned hierarchically • Leptons from semi-leptonic decay ( b  c W-, W-ene) • Kaons From Cabibo-favored hadronic cascade ( b c s ) • Neural net (1 and 2) • Low-momentum leptons, soft pions, additional kaons • Efficiency and mistag rates are determined from B0 decays • Parameters in sin2b, DmB0 Likelihood fits • Cross-checked with B0 D*ln efficiency w = mistag rate Q = e(1-2w)2 David Nathan Brown 15Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  16. Dt Resolution • Dt ≈ Dz/bgc • Dz from vertex difference • Tag B0 z resolution ~180 m • Signal B0 z resolution ~70 mm • Resolution modeled with 3 Gaussians • Core,Tail, and Outliers •  scaled to vertex error estimate (core and tail) • Shifts from 0 allowed (charm vertex flight) • Fit Parameters in sin2b, DmB0 Likelihood fits David Nathan Brown 16Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  17. B0 B0 Mixing Result (Preliminary) • Fit for DmB0 + 33 parameters for tagging effects and Dz resolution for signals and backgrounds DmB0 = 0.519 ± 0.020 ± 0.016 ps-1 David Nathan Brown 17Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  18. Comparison with Other Results This Result David Nathan Brown 18Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  19. CP Rates by Mode and Tag David Nathan Brown 19Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  20. sin2b Extraction CP = -1 sin2b = 0.24 ± 0.22 ± 0.05 CP = 1 • Fit for sin2b + 33 parameters for tagging effects and Dz resolution for signals and backgrounds sin2b = 0.86 ± 0.51 ± 0.14 sin(2b) = 0.34 ± 0.20 ± 0.05 David Nathan Brown 20Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  21. Systematic Errors and Cross-Checks • No significant differences are seen dividing sample by tagging mode, signal mode, decay mode, … • No significant direct CP violation • No CP asymmetry in fits to B± samples David Nathan Brown 21Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  22. Comparison with Other Results This Result New World Average David Nathan Brown 22Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  23. CKM Constraints Vub ≈ Al3(r-ih) (Wolfenstein parameterization) David Nathan Brown 23Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  24. Conclusions • BaBar has measured DmB0and sin2b in ~21 fb-1 of recorded ¡(4S) decays • Most precise single measurement of sin2b • Consistent with other measurements and world average • World average sin2b is now 3 s away from 0 • BaBar is running again since February 1 • 0.6 fb-1 recorded so far • Peak luminosity ~1X1033/cm2s • We expect an additional ~30 fb-1of data by August David Nathan Brown 24Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  25. Mixing and sin2b measurements are done with the same strategy: do a global fit to all the events that can carry information: Mixing : tagged flavour eigenstates sin2b : tagged flavour and CP eigenstates We float in the fit as many parameters as possible Only in CP fit Only in mixing Biggest correlation with sin2b 7.6% David Nathan Brown 25Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

  26. J/YKL composition Inclusive J/Y MC J/Y sidebands David Nathan Brown 26Les Rencontres de Physique de la Vallée d'Aoste7 March, 2001

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