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D 0 - D 0 Mixing at B A B AR

D 0 - D 0 Mixing at B A B AR. Amir Rahimi The Ohio State University For B A B AR Collaboration. Outline. Introduction to mixing Motivation for using this mode Mixing formalism in a multibody decay Lifetime fit and mixing results. D 0 -D 0 Mixing with. Introduction.

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D 0 - D 0 Mixing at B A B AR

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  1. D0-D0 Mixing at BABAR Amir Rahimi The Ohio State University For BABAR Collaboration

  2. Outline • Introduction to mixing • Motivation for using this mode • Mixing formalism in a multibody decay • Lifetime fit and mixing results D0-D0 Mixing with Charm2006

  3. Introduction • The mass eigenstates and have different masses and lifetimes • Signs of new physics: • Observation of CP violation Time integrated mixing rate: Charm2006

  4. Decay Mode • Obtain a pure sample by reconstructing: • In cc-bar events • Obtain the flavor of D0/D0bar from charge of pslow • Right-sign Cabibo-favored (CF) D0K-p+p0used for normalization • Wrong-sign D0K+p-p0 has contributions from doubly Cabibo-suppressed (DCS) decays and CF mixed decays • Separate signal from background by fitting to m(Kpp0) and DM = m(Kpp0ps) – m(Kpp0) Charm2006

  5. Branching Ratio • In non-leptonic search for D mixing, DCS obscure the signs of mixing: • Consider • Belle • BABAR • Compare to the standard decay D0K+p- hep-ex/0507071 preliminary Charm2006

  6. Resonance Contributions u • The resonance amplitudes are different for DCS and CF- there is more sensitivity to mixing • In D0 K-p+p0 the main resonance is K-r+ • In D0 K+p-p0 the main resonance is K*+ p- r+, p+ CF d W + c s K-, K*- u u u K*+, K+ s s s DCS W + d c p-,r- u u Charm2006

  7. Event-level tagging • To do a Dalitz analysis need to reduce the large peaking background in DCS • Real D0’s with uncorrelated slow pions • Use an event-level tag • Require a second tag in the opposite event hemisphere • Use K+, p±s, e±, and m±, in the other side of the event • Provides consistency check on p+tag p+ p0 K- +tag beamspot D0 interaction point D0 -tag K+tag e-tag m-tag Charm2006

  8. Event-Level Tagging • Using an event-level tag significantly reduces background • Use K+, p±s, e±, and m±, in the other side of the event • Never done before in this type of analysis  Charm2006

  9. Event-Level Tagging • With this second tag, we can now look at the resonance contributions  Charm2006

  10. Resonance Contributions D0 K+p-p0 D0 K-p+p0 • Event-level tagged • Prominent K* peak in DCS Mode Charm2006

  11. Resonance Contributions D0 K+p-p0 D0 K-p+p0 • Event-level tagged • Prominent r peak in CF Mode r Charm2006

  12. Selection of Phase-Space Regions • Based on inspection of the Dalitz plots, we exclude events in the regions: • 850 < m(Kp) < 950 MeV/c2 • 850 < m(Kp0) < 950 MeV/c2 • entire allowed phase-space region • selected phase-space region for mixing analysis Preliminary D0 Cand. D0 Cand. WS (7.5 ± 0.5) x 102 (8.1 ±0.5) x 102 RS (3.648 ± 0.007) x 105 (3.646 ± 0.006) x 105 (b) WS (3.8 ± 0.36) x 102 (3.79 ±0.36) x 102 RS (2.518 ±0.006) x 105 (2.512 ±0.006) x 105 (a) Charm2006

  13. Decay Time with Mixing • At any particular point in phase space (Dalitz Plot): • Integrating over an arbitrary region of phase space: (a is the suppression factor) Charm2006

  14. Consider CP Violation • We account for possible CP violation by fitting D0 and D0 separately and making the substitutions: (a and b are the suppression factors) Charm2006

  15. PDF Fit to Decay Times • Data after a statistical background subtraction Decay times in a signal region Charm2006

  16. Preliminary Mixing Results CP Conserved hep-ex/0605046 Contours determined using DlogL levels • RM < 0.054%upper limit at 95% confidence level (determined using DlogL ) • Consistent with no mixing at 4.5% confidence level (determined using a frequentist method) Charm2006

  17. Preliminary Mixing Results CP Violation Allowed • Contours determined using DlogL levels Charm2006

  18. Summary and Outlook • Performed the first analysis of D0 K-p +p 0 • Uncovered the DCS Dalitz plot • Time-dependent Dalitz plot analysis of this mode is underway • Additional BABAR mixing results coming up soon: • Semi-leptonic mixing using doubly-tag analysis • D0  K-p + • D0  K-p +p +p - • An observation of D mixing may be on the horizon Charm2006

  19. Charm Mixing in The Standard Model • Box Diagram SM Charm Mixing is expected to be very low • Long distance SM predictions accommodate higher rates V*ci Vui d, s, b u c D0 D0 W W d, s, b u c Vuj V*cj SM Mixing: box diagram SM Mixing Predictions u u u p+ D0 mixing rate = |amplitude|2 c d d W+ :x=DM/G c d d W- p- : y=DG/2G D0 u u u SM Mixing: a long-range contribution (Plot courtesy of A. Petrov, hep/ph 0311271) Charm2006

  20. Fit to the CF Events • ML Fit and data projected in signal regions 1.85 < m(Kpp0)< 1.88 GeV/c2 0.145 < DM < 0.146 GeV/c2 Charm2006

  21. Upper Limit on RM • We use DlogL to set an upper limit • Behavior near zero consistent with a frequentist method • Straight forward to compare with other experiments Charm2006

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