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Koji Hara (KEK) For the Belle Collaboration

Koji Hara (KEK) For the Belle Collaboration. Time Dependent CP Violation in B 0 → p + p - Decays [hep-ex/0502035]. Time dependent CP-violating parameters in B 0 → p + p − decays. S pp : B 0 B 0 mixing induced CPV. A pp : direct CPV.

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Koji Hara (KEK) For the Belle Collaboration

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  1. Koji Hara (KEK)For the Belle Collaboration Time Dependent CP Violation in B0→p+p- Decays [hep-ex/0502035]

  2. Time dependent CP-violating parameters in B0→p+p− decays Spp: B0B0 mixing induced CPV App: direct CPV In B0→p+p- decays, Spp is sensitive to f2 (a): penguin tree W u b d d g u can be determined with isospin relations W u u Direct CP violation may occur.

  3. Previous experimentalsituation BABAR 227M BB Belle152 M BB with 372±32 B0→p+p− events with 467±33 B0→p+p− events hep-ex/0501071 PRL 93, 021601 (2004) CPV with 5.2s, 3.2s evidence for DCPV 3.2s difference

  4. New Belle measurement with 275M BB pairs • additional data • 152 → 275 M BB pairs • the inner tracker and interaction region was replaced in the summer 2003 • 3-layer SVD (152 M BB) to 4-layer SVD with small-cell drift chamber (123 M BB). • Analysis procedure is basically same as before

  5. Event Selection Pion Identification using aerogel and dE/dx • B0→p+p− selection Kinematical Selection corresponding ±3s Flavor Tagging q=+1 tagged as a B0, q=−1 tagged as a B0 q: flavor charge r: flavor tag quality r=0 no flavor discrimination, r=1 unambiguous flavor assignment 0<r≤1

  6. qq BB qq e- e+ Other B e+ e- Signal B Event Selection (continuum suppression) Event shape B flight direction Spherical Jet-like (Likelihood Ratio) LR

  7. LR (Likelihood Ratio) B0→p+p− signals (LR>0.86) (LR<0.86) r (flavor tag quality) 2,820 candidates containing (666  43)p+p-signal events

  8. B0 tagged Unbinned CP Fit Result Background subtracted fit projection for all events Points: DE-Mbc 2D fits to individual time intervals B0 tagged p+p− Yield p+p− ACP Dt (ps)

  9. Consistency checks with Time-integrated fits consistent with time-dependent fit LR>0.86 & 0.5<r≤1.0 B0 tagged B0 tagged pp: 107±13 pp: 69±11 Kp: 42±9 Kp: 43±9 cont: 38±1 cont: 38±1 DE (GeV) Direct CP Violation is evident!

  10. Dt distribution and raw asymmetry LR>0.86 0.0<r≤0.5 q=+1 Events /(1.25ps) Raw asymmetry q=−1 0.5<r≤1.0 -5 0 +5 Dt (ps) 0 -5 +5

  11. Significance calculation with Feldman-Cousins method Large CP Violation, App (A,S)=(0,0) 1-C.L.=5.62x10-8, 5.4s (A,S)=(0,−0.62) 1-C.L.=5.13x10-5, 4.0s Large Direct CP violation, confirmation of the previous Belle results Spp both statistical and systematic errors are taken into account. C.L. = Confidence Level

  12. New experimental situation App Belle 275M ~2.3s difference between Belle and BABAR BABAR 227M Spp

  13. Interpretation: f2 constraint using isospin M. Gronau and D. London, PRL 65, 3381 (1990) The cleanest method to extract f2 We use the HFAG summer 2004 values for the branching ratios of B0→p+p−, p0p0, B+→p+p0 and direct CP asymmetry of B0→p0p0. We use the statistical treatment of J. Charles et al., hep-ph/0406184

  14. Interpretation : f2 constraint usingisospin using HFAG summer 2004 1−C.L. J. Charles et al., hep-ph/0406184 f2 (degrees) 95.4% confidence interval and

  15. Summary of new Belle B0 →p+p− CP results • The fit yields • Large direct CP violation with 4.0s significance is observed • The results confirm the previous Belle results. • Isospin analysis gives at 95.4% C.L. & [hep-ex/0502035]

  16. backup slides

  17. Probability Density Functions (PDFs) for the CP fit a likelihood function are event fractions as functions of DE and Mbc is maximized. two free parameters: App and Spp

  18. Probability Density Functions (PDFs) for the CP fit For p+p− wrong tag fraction obtained from data For K+p− HFAG2004 For qq backup is set to 0 in default

  19. New experimental situation App combined 140fb-1 113fb-1 inside the physical boundary! ~2.3s difference between Belle and BaBar BaBar 227M

  20. Future prospect Lpeak = 1.41034cm-2s-1 Ltot = 350fb-1 (Feb.8, 2005) ~1010 BB/year !! & similar number oft+t- world records ! Major upgrade of KEKB & Belle detector (>1yr shutdown) SuperKEKB Crab cavities Lpeak (cm-2s-1) Lint 5x1034 ~1 ab-1 1.4x1034 330 fb-1 5x1035 ~10 ab-1

  21. Future prospect assuming the current measured values Current ~0.5ab-1 ~2ab-1 ~8ab-1 ~32ab-1 Super-B factories can pin down the f2 value.

  22. Validity check with B0→K+p− We extract B0→K+p− events ps Lifetime fit LR>0.86 ps-1 in total 4,293 (including 2,207 K+p−) events (OF-SF)/(OF+SF) good control sample because of the similar topology to B0→p+p− Dt (ps) consistent with the WA values

  23. Background asymmetry pp sideband Kp sideband B0:43577, B0b:43308 B0:42467, B0b:42090 No background asymmetry possible background asymmetries are included in the systematic error

  24. Systematic errors including uncertainties in the b.k.g and Final State Radiation O. Long, M. Baak, R.N. Cahn, and D. Kirkby, PRD 68, 034010 (2003)

  25. Validity check (lifetime fit with B0→p+p−) Lifetime fit ps 2820 events B0→p+p− continuum good agreement with the World Average (W.A.) Value ps PDG2004

  26. Validity check with B0→K+p− total 4293 events CP fit results B0: 2106, B0b: 2187 consistent with the WA value Raw ACP in agreement with null asymmetry Dt (ps)

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