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Hot Topics from the Belle Experiment

Hot Topics from the Belle Experiment. Contents. Introduction to the Belle experiment CP violation in B 0  f K S Evidence of B 0  p 0 p 0 New resonance X (3872) Summary. Introduction to the Belle Experiment. KEKB Accelerator. 3.5 GeV e +  8.0 GeV e -

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Hot Topics from the Belle Experiment

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  1. Hot Topicsfrom the Belle Experiment Takeo Higuchi, KEK BEAUTY2003

  2. Contents • Introduction to the Belle experiment • CP violation in B0fKS • Evidence of B0 p0p0 • New resonance X(3872) • Summary

  3. Introduction to the Belle Experiment

  4. KEKB Accelerator • 3.5 GeV e+8.0 GeV e- • e+e-(4S) with bg = 0.425. • Crossing angle = ±11 mrad. World Records e- e+ L = (1.061034)/cm2/sec  Ldt = 158 fb-1On-resonance 140 fb-1 3km circumference History 1999 Jun 2003 Jul

  5. Belle Detector Aerogel Cherenkov Counter n = 1.015~1.030 Electromagnetic Calorimeter CsI(Tl) 16X0 3.5 GeV e+ TOF counter 8.0 GeV e- Central Drift Chamber Tracking + dE/dx 50-layers + He/C2H5 KLm detector 14/15 layer RPC+Fe Si Vertex Detector 3 layer DSSD

  6. People 274 authors, 45 institutions many nations

  7. CP Violation in B0 fKS

  8. CP Violation by Kobayashi-Maskawa KM ansatz: CP violation is due to complex phase in quark mixing matrix h unitarity triangle CP violation parameters (f1, f2, f3) = (b, a, g) O r

  9. Time-Dependent CP Asymmetry S= -xfsin2f1: SM prediction A = 0 or |l| = 1  No direct CPV Inputs: xf = -1, S = 0.6 A= 0.0

  10. New Physics Hunting in b sqq SM predicts same CPV in b ccs and sqq. New physics may deviate CPV in b ccs from sqq New process w/ different CP phase SM penguin f + e.g.) squark penguin Deviation from b  ccs Hint of new physics

  11. b ccs Reconstruction Detail by K.Miyabayashi b ccsw/o J/KL 140 fb-1, 152MBB pairs Beam-energy constrained mass (GeV/c2) B 0 J/KL J/ KL signal 5417 events are used in the fit. pB*(cms)

  12. CP Violation in b ccs Detail by K.Miyabayashi 5417 events @ 152M BB poor flavor tag Small systematic uncertainty  Well controlled analysis technique fine flavor tag consistent with no direct CPV K. Abe et al. [Belle collaboration], BELLE-CONF-0353.

  13. b sqq Reconstructions • B0 fKS:fK+K, KS  p+p • Minimal kaon-identification requirements. • Belle standard KS selection. • | M(KK)  M(f) | < 10MeV/c2(mass resolution = 3.6 MeV/c2). • | pf | in CMS > 2.0 GeV/c. • Belle standard continuum suppression (given later.) • | DE | < 60MeV, 5.27 < Mbc < 5.29 GeV/c2. M(KK) [GeV/c2] • Background is dominated by continuum • CP in the background: • K+K-KS: (7.2±1.7)% • f 0(980)KS: • These effects are included in the systematic error.

  14. b sqq Reconstructions - Cont’d • B0K+KKS • More stringent kaon-identification requirements. • Particle veto for f,D0,c0, and J/  K+K and D+  K+KS. • Belle standard continuum suppression. • | DE | < 40 MeV, 5.27 < Mbc < 5.29 GeV/c2. • B0h´KS: 1) h´rg, rp+p2)h´hp+p, hgg • Belle standard continuum suppression. • |DE| < 60MeV (h´rg);100 < DE < +80 MeV (h´hp+p)5.27 < Mbc < 5.29 GeV/c2

  15. Beam-Energy Constrained Mass 6811 signals 106 candidates for S and A fit purity = 0.640.10 efficiency = 27.3% B0 fKS 19918 signals 361 candidates for S and A fit purity = 0.550.05 efficiency = 15.7% B0 K+K-KS B0 hKS 24421 signals 421 candidates for S and A fit purity = 0.580.05 efficiency = 17.7% (h´ hp+p) 15.7% (h´ rg )

  16. Unbinned Maximum Likelihood Fit signal background • fsig: Event by event signal probability • 2. Psig: • 3. R: Dt resolution function • 4. Pbkg: Background Dt distribution

  17. CP Violation in b sqq Fit sin2f1 @ 152M BB B0 fKS B0K+K-KS B0h’KS BfCP(sqq) decay vertices are reconstructed using K- or p-track pair.

  18. Consistency Checks • CP violation parameters with A = 0 • B0 fKS: -xfS = -0.99 ± 0.50 • B0 K+K-KS: -xfS = +0.54 ± 0.24 • B0 hKS: -xfS = +0.43 ± 0.27 • Null asymmetry tests for S term • B+ fK+: -xfS = -0.09 ± 0.26 • B+ hK+: -xfS = +0.10 ± 0.14 Less correlation btw S and A Consistent with S = 0

  19. Statistical Significance • B0K+K-KS, h´KS • Consistent with sin2f1. • B0 fKS • 3.5s deviation (Feldman-Cousins). • S(fKS) = sin2f1: 0.05% probability. sin2f1 • Hint of new physics? • Need more data to establish conclusion. K. Abe et al. [Belle collaboration], hep-ex/0308035, submitted to Phys. Rev. Lett.

  20. Evidence of B0p0p0

  21. Disentanglingf2 B0 p+p- is one of promising decays to measure f2 Two possible diagrams require measured f2 disentangled u u P T d u W t b u b d W Penguin-polluted CP violation Br(B0p0p0) measurement gives constraint on q.

  22. B0 reconstruction 2 p0’s with 115 < M(gg) < 152 MeV/c2. Efficiency = 9.90 ± 0.03%. Those MC-determined distributions are used in extraction of signal yield with calibration using B+ D0p+ decays in data. B0 p0p0 Reconstruction Signal MC Signal MC Mbc [GeV/c2] DE [GeV]

  23. Continuum Suppression Signal MC Continuum Fisher Fisher Construct likelihood e+e- BB e+e-  qq B flight direction |cosqB| • 1-cos2q for BB • flat for qq Multi-dimensionallikelihood ratio Flavor tag quality |r| • r = high  well tagged originated from B decay • r = low  poorly tagged originated from qq

  24. B+ r+p0 Contamination According to MC study, other charmless decays than B+ r+p0 are negligible. B+ r+p0 • DE-Mbc shape: MC-determined 2-dimensional distribution. • Yield: Recent Br measurement with MC-determined efficiency. p+p0 DE [GeV] Mbc [GeV/c2] B+ r+p0 charmless background incl. r+p0 Br(B+ r+p0) measurement: B. Aubert et al. [BaBar collaboration], hep-ex/0307087, submitted to PRL.

  25. Signal Extraction @ 152 M BB B+ r+p 0 (modeled by MC) Continuum Mbc [GeV/c2] DE [GeV] Signal Unbinned maximum likelihood fit Signal shape is modeled by MC, and is calibrated using B+ D0p+ decays in data. Signal yield: Branching fraction Significance incl. systematic error = 3.4s S.H.Lee, K.Suzuki et al. [Belle collaboration], hep-ex/0308040, submitted to Phys. Rev. Lett.

  26. New Resonance X(3872)

  27. New Narrow Resonance: X  p+p-J/y • Mass distribution: Data MC y(2S) y(2S) • g conversion elimination Events / 0.010 GeV/c2 X [GeV/c2] [GeV/c2] New resonance X is found.

  28. B+ K+X @ 152M BB • B+ K+X reconstruction • Add loosely identified kaon to X. 3-dim. unbinned likelihood fit. MppJ/y DE Mbc 5.20 5.25 5.30 3.84 3.88 3.92 0.0 0.2 [GeV/c2] [GeV] [GeV/c2]

  29. What is X? • Hypothesis I: 13D2 • M(X) = 3872 MeV/c2 differs fromprediction: M(13D2) = 3810 MeV/c2. • G(13D2gcc1)/G(13D2ppJ/y) ~ 5, while G(Xgcc1)/G(XppJ/y) < 1 Mbc E.Eichten et al., Phys. Rev. D21, 203 (1980); W.Buchmüller and S.-H.H.Tye, Phys. Rev. D24, 132 (1981). M(gcc1) No clear signal

  30. What is X? - Cont’d • Hypothesis II: “molecular” charmonium • M(X) = 3872 ± 0.6 ± 0.5 MeV. • M(D0) + M(D0*) = 3871.2 ± 1.0 MeV. • Do above facts suggest loosely bound D0-D0* state? • Need more data to conclude. q q D0-D0* “molecule” Q Q S.-K.Choi, S.L.Olsen et al. [Belle collaboration], hep-ex/0309032, submitted to Phys. Rev. Lett.

  31. Summary

  32. 3.5sdeviation is observed with Feldman-Cousins in CP violation in B0 fKS from the SM. Hint of new physics? Br(B0 p 0p 0) = (1.7±0.6±0.2)×106 is measured, which gives constraint on penguin uncertainty in f2. New resonanceof X  p+p-J/y is observed at M(X) = 3872.0±0.6±0.5 MeV/c2 that does not look like cc state. Summary

  33. Backup Slides

  34. Mixing-Induced CP Violation Sanda, Bigi & Carter s f Vtb Vts W b s t B0 g s d KS d  s V* f Vtb Vts td Vtb W b t b s t B0 B0 g W W s d t d KS V* Vtb d td

  35. How to Measure CP Violation? Detail by K.Miyabayashi e-: 8.0 GeV e+: 3.5 GeV fCP BCP e- e+ ¡(4S) bg ~ 0.425 Btag DzcbgtB ~ 200 mm flavor tag Dz • Find BfCP decay • Identify (= “tag”) flavor of BfCP • Measure decay-time difference: Dt • Determine asymmetry in Dt distributions

  36. Systematic Error of CPV in b ccs Small uncertainty in analysis procedure stat err. = 0.057

  37. B0  K+K-KS: CP = 1 Mixture Since B0K+K-KS is 3-body decay, the final state is a mixture of CP = 1. How can we determine the mixing fraction? CP = 1 fraction is equal to that of l =even/odd CP = +1 CP = +1 K+ J=0 J=0 J=0 decay l CP = (-1)l B0 KS l K- J=0

  38. B0  K+K-KS: CP = 1 Mixture - Cont’d • l-evenfraction in |K0K0> can be determined by |KSKS> system • Using isospin symmetry, CP = +1 l = even l = odd CP even

  39. Dt Distributions B0 fKS B0K+K-KS B0h’KS qxf = -1 qxf = -1 qxf = -1 qxf = +1 qxf = +1 qxf = +1 Dt [ps] Dt [ps] Dt [ps]

  40. Systematic Errors of CPV in b sqq fKS h'KS KKKS S A S A S A Wtag fractions ±0.018 ±0.007 ±0.005 ±0.006 ±0.005 ±0.007 Physics parameters ±0.033 ±0.002 ±0.006 ±0.002 ±0.003 ±0.003 Vertexing ±0.022 ±0.046 ±0.016 ±0.027 ±0.044 ±0.024 Background fraction ±0.053 ±0.035 ±0.045 ±0.026 ±0.029 ±0.036 Background Dt ±0.015 ±0.008 ±0.003 ±0.003 ±0.010 ±0.006 Resolution function ±0.013 ±0.005 ±0.004 ±0.003 ±0.007 ±0.004 KKKs + f0Ks bkg. +0.001 ±0.039 -0.084 Sum +0.09 ±0.07 ±0.05 ±0.04 ±0.05 ±0.04 -0.11 Systematics are small and well understood from b  ccs studies.

  41. Systematic Uncertainty

  42. M(p+p-) Distribution Fit to r-mass is pretty good M(p+p-) [GeV/c2] • M(p+p-) can be fitted by r-mass distribution well. • 13D2rJ/y is forbidden by isospin conservation rule.

  43. Belle Preliminary Constraint on q M.Gronau et al., Phys. Lett. B 514, 315 (2001). Using Our Results • B+0/B+- = 1.04 • B00/B+- = 0.39 • App = 0.57

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