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Exploring CP Violation and New Physics at Belle Experiment

This article delves into key findings from the Belle Experiment, such as CP violation in B0 decays, evidence of B0 to p0p0 decays, and the discovery of the new resonance X(3872). Detailed explanations of the experiment setup, analysis techniques, and results are provided, shedding light on the hunt for new physics. The significance of CP violation in b→sqq decays is discussed, along with reconstructions and statistical analyses. The data presented hint at potential new physics phenomena, emphasizing the need for further research for conclusive evidence.

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Exploring CP Violation and New Physics at 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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