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CP Violation Studies in B 0 D (*)  in B A B A R and BELLE

CP Violation Studies in B 0 D (*)  in B A B A R and BELLE. Dominique Boutigny LAPP-CNRS/IN2P3 HEP2003 Europhysics Conference in Aachen, Germany July 17-23, 2003. Theoretical Motivation. It is important to check the consistency of the CKM mechanism Over-constrain the Unitarity Triangle

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CP Violation Studies in B 0 D (*)  in B A B A R and BELLE

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  1. CP Violation Studies in B0D(*) in BABAR and BELLE Dominique Boutigny LAPP-CNRS/IN2P3 HEP2003 Europhysics Conference in Aachen, Germany July 17-23, 2003

  2. HEP2003 Theoretical Motivation • It is important to check the consistency of the CKM mechanism • Over-constrain the Unitarity Triangle • Measure the angles W.A. Charmonium modes: sin(2) = 0.734  0.055 - CP Violation is now well established  Should measure other angles This talk

  3. HEP2003 • b  u transition  relative weak phase  between the 2 amplitudes • Mixing  2 • Relative strong phase  between the 2 amplitudes  Measure sin(2+) CP violation proportional to: CP Violation in B0D(*)  CP violation appearing in interference between 2 amplitudes • Final states are not CP eigenstates • No penguin pollution Dominant diagram b  c transition Suppressed diagram b  u transition

  4. HEP2003 Determination of sin(2+) from Time Dependent Evolution • Time evolution for D-+ final states: • Time evolution for D+-final states: • Similar equation for D*  Need to know both S andS to determine (2+) and   There are four ambiguities in (2+) determination

  5. HEP2003 With fully reconstructed B0D(*) Advantages: Small background But: relatively small number of events N(D) = 5207  87 Purity = 85 % N(D*) = 4746  78 Purity= 94 % Background mainly from combinatorics Peaking background mainly from B+ D(*)0+ (~1%) Experimental Technique (1) BaBar

  6. HEP2003 With partially reconstructed B0D*+- +f D*- X B0 D0 -s Experimental Technique (2) signal BaBar BELLE D* combinatoric • Using: • Soft pion • Fast pion • Beam constraints • Reconstruct missing mass peaking at the D0 mass Other peaking Continuum • Advantages: • More statistics: • Lepton tag: 6406  129 events • Kaon tag: 25157  323 events • But … • More background

  7. HEP2003 Experimental Technique (3) At time of BTAG decay, the 2 B’s are in opposite flavor states bg = 0.56 K+ Coherent B0B0 production - Reco B K+ -s Tag B z U(4s) Dz Fully reconstruct one Bin Dor D* Vertex determined using all tracks Or partially reconstruct one B in D* Vertex determined using the fast  only and a beam spot constraint + Dt @Dz/gbc Reconstruct vertex of BTAG and compute proper time difference Dt@Dz/gbc Determine flavor of other B meson BTAG (“tagging”) Using Kaon or lepton charge correlation

  8. HEP2003 Simultaneous determination of sin(2+) and r(*) is not possible with the current statistics Use B0Ds(*)+-(I. Dunietz, Phys. Lett. B 427, 179 (1998)) and SU(3) symmetry SU(3) Difficulties (1)Determination of Amplitude Ratio: r BaBar – hep-ex/0207053 (2002) Add another 30% systematic error for SU(3) breaking uncertainty and for missing W-exchange diagrams in calculation

  9. HEP2003 We use b  u interference effects on the reco side to measure sin(2+) The same kind of interference effects exist in the tag side (Long, Baak, Cahn, Kirkby hep-ex/0303030, accepted by PRD) Induces time-dependent effect Change the time-dependent PDFs r and r' can be of the same order of magnitude Lepton tags have no problem Kaon tags are affected For r = r' = 0.1 ( 5 the expected value): No sine terms Reco-side only Reco-side and tag-side Difficulties (2)b  u interference effects in the tag side signal side tag side

  10. HEP2003 Re-Parameterization • Due to the tag side b  u interference effect, one needs to change the parameters in the time dependent decay rate formulas • a: Independent of tag side effects • b and c: absorb the tag side interferences • For lepton tags: Define: Handle on phase 

  11. HEP2003 D*+ - D*- + B0 B0 D*- + D*+ - B0 B0 Time Dependent Fits in BaBar Partially reconstructed B  D* Fully reconstructed B  D(*) Fit is performed in 4 steps in order to determine the signal yield, the background contributions and the CP parameters Unbinned ML fit to t spectra: 48 parameters – 13 parameters for the a,b and c coefficients (D, D* , Kaon tags, lepton tag) Lepton tags Lepton tags D(*)+ - D(*)- + B0 B0 D(*)- + D(*)+ - B0 B0

  12. HEP2003 Results for Fully Reconstructed B  D(*) in BaBar (1) Based on 81.9 fb-1 on-resonance events From the fit to t spectra  30% additional theoretical error assigned to r and r* values From BaBar measurement of B0 DS(*) Systematic uncertainties

  13. HEP2003 Minimum at |sin (2+)| = 0.98 Results for Fully Reconstructed B  D(*) in BaBar (2) 2 is highly non-parabolic  Use a toy Monte-Carlo approach to interpret results in terms of confidence levels for |sin (2+)| Minimize a 2 with respect to (2+), [D], [D*], r and r* BaBar BaBar

  14. HEP2003 Results for Partially Reconstructed B  D* in BaBar (1) Based on 76,4 fb-1 on resonance events • Lepton tag  fit S andS • Kaon tag  fit a, b and c Combining lepton and Kaon results: Deviates from 0 by  2.1 Systematic uncertainties

  15. HEP2003 Results for Partially Reconstructed B  D* in BaBar(2) • Minimize a 2 to determine |sin (2+)| and  • Interpretation in terms of C.L. using a toy Monte-Carlo approach BaBar

  16. HEP2003 Assuming 30% theoretical error on r(D) and r(D* ) One can also plot the lower limit on |sin((2+)| as a function of r In this case, r(D) = r(D* ) is assumed Combined BaBar Results BaBar BaBar No error on r assumed

  17. HEP2003 Status of B D(*) in BELLE • Similar studies on B D(*) are being performed by BELLE: • For the partial reconstruction technique: • With 78 fb-1BELLE is expecting a statistical error of: (2r.sin(21+3)) = 0.029 • For the full reconstruction technique • With the full data sample available this summer, BELLE is expecting: (2r.sin(21+3)) =0.028 • Computed from the data • Includes background effects • Estimated from the MC • Does not include background effects

  18. HEP2003 Summary • A study of time dependent CP asymmetry in B0D(*)+- has been performed by BaBar using both partial and full reconstruction techniques • With full reconstruction: • A limit is set at:|sin (2+)|>0.69 @ 68.3% C.L. • No limit is set at 90% CL • With partial reconstruction: • A limit is set at:|sin (2+)|>0.75 (0.62) @ 90 % (95 %) C.L. • Combining both methods: • |sin (2+)|>0.89 (0.76) @ 68.3 % (90%) C.L. • |sin (2+)| = 0 is excluded @ 99.5% C.L. • Limits are also set as a function of the ratio between favored and suppressed amplitudes: r • Similar studies are going on in BELLE, results will come soon…

  19. HEP2003 Constraints in the ,  Plane from BaBar Measurements Constraint from sin(2+) assuming a given value of r with 30% theoretical error

  20. Backup Slides

  21. HEP2003 Monte-Carlo ValidationFully Reconstructed Method No generated asymmetry: a=b=c=0 9.4x data statistics for B D and 6.9x data statistics for B  D*  Generated asymmetry: a=0.04 b=c=0 4.6x data statistics for B D and 3.8x data statistics for B  D*   No significant biases observed

  22. HEP2003 Monte-Carlo ValidationPartially Reconstructed Method

  23. HEP2003 CP Asymmetry with Partial Reconstruction Method in BaBar CP asymmetry leptons Kaons

  24. HEP2003 Partial Reconstruction Method Cross-Check – Mixing Asymmetries

  25. HEP2003 Measurement of B0 Lifetime withPartially Reconstructed B  D* in BaBar • B0 lifetime has been measured in BaBar with partially reconstructed B  D* events • hep-ex/0212012 - Phys.Rev.D67:091101,2003 B0 = 1.533  0.034 (stat)  0.038 (sys) ps • In good agreement with World Average: B0 = 1.542  0.016 ps

  26. Impact of a Dt bias • The problem: if we get Dt wrong by dt (<<1/DMd) • cos(DMdDt)+S sin(DMdDt)  cos(DMdDt)+(S-DMddt)sin(DMdDt) • A bias of 10mm would cause a shift dsin(2b+g)=0.75 • NOTE: given the sign combinations only the “c” parameters are biased • The answer: we let the Dt biases free in the fit and we are therefore insensitive to dt • The objection: can you prove that you are insensitive to it also if the resolution function is different from your model (3 Gaussians) • The proofs: • SVT misalignment tests: we include in the systematic error the variation due to using different misalignments in MC. They represent very different resolution function. They correspond to dt<4mm  the scale of the possible bias is dsin(2b+g)=0.3 and it is anyhow accounted for in the error • Toy MC test: since in our model biases are proportional to sDt toys have been generated with flat 10mm biases. Fit results show biases dc<0.005, 15% of the systematic error assigned to these parameters

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