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CP Violation

CP Violation. João R. T. de Mello Neto. Recent results and perspectives. Instituto de Física Universidade Federal do Rio de Janeiro. 22-26 July,2003. Outline. Introduction CP Violation in the SM Measurement of β B Factories results Other measurements

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CP Violation

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  1. CP Violation João R. T. de Mello Neto Recent results and perspectives Instituto de Física Universidade Federal do Rio de Janeiro 22-26 July,2003

  2. Outline • Introduction • CP Violation in the SM • Measurement of β • B Factories results • Other measurements • Dedicaded hadron colliders experiments • LHCb, BTeV • Conclusion

  3. Motivations CP violation is one of the fundamental phenomena in particle physics CP is one of the less experimentally constrained parts of SM SM with 3 generations and the CKM ansatz can accomodate CP CP asymmetries in the B system are expected to be large. Observations of CP in the B system can: test the consistency of SM lead to the discovery of new physics Cosmology needs additional sources of CP violation other than what is provided by the SM.

  4. I will not talk about: • Kaon physics • Strong CP problem; • CP violation in the charm sector; • CP violation in Cosmology! Concentrate in CP violation in the B sector (Only a small subset!)

  5. Huge experimental effort D0 2001 BTEV ? ATLAS 2008 1999 BELLE CLEO 3 1999 Plus hundreds of experimental groups around the World.

  6. t b d w- w- b d t e- w- c b d d Matter – antimatter oscillations Neutral B0mesons oscillate ordinary ΔB=1 interactions exchange of virtual q (2/3) t : dominant amplitude ΔB=2 decay Δmd Vtd fB decay constant BB Bag factor

  7. = = Weak decay phase mixing phase mixing phase CKM matrix The quark electroweak eigenstates are connected to the mass eigenstates by the CKM matrix : four parameters A, λ, ρ, η

  8. (,) In SM:  Vtd Vub   Vcb (1,0) (0,0) In SM: Vtd Vub Vts   Unitarity triangles VtdVtb+VcdVcb+Vud Vub= 0 VtdVud+VtsVus+Vtb Vub= 0 • measure all the angles • measure all the sides • SM: consistency!

  9. CP violation • Three possible manifestations of CP violation: • Direct CP violation • (interference between two decay amplitudes) • Indirect CP violation • (interference between two mixing amplitudes) • CP violation in the interferencebetween mixed and unmixed decays

  10. time-dependent formalism for Bd decay amplitude for time evolution CP violation: interference between mixing and decay

  11. time-dependent formalism for Bd B-factories: Δt LHCb, BTeV: t S=+sin(2β) B0→J/ψKS C=0 SM: B0→J/ψKL S=-sin(2β) C=0

  12. Measuring β Decays such as B0→J/ψKS and B0→J/ψKL theoretically well understood: tree and leading penguin have same phase “relatively simple” experiment

  13. Measuring β (from D. Lange)

  14. Assimetric colliders at B factories: Belle, BaBar One year: ~ 100 M pairs Belle 132 fb-1 BaBar 117 fb-1 March, 2003 Coherent production

  15. KEKB Luminosity achieved: 1.06 x1034cm-2s-1

  16. Babar detector

  17. 8K events 12K events Mixing and lifetimes large samples of • hadronic decays: fully or partially reconst. • semileptonic decays (D* l n) fully or partially reconst. • dileptons 29 fb-1

  18. Δt distributions and lifetimes Δt = proper time difference between the decay times of the two B-mesons Δt resolution of ~ same order of magnitude as lifetime t0 = 1.554  0.030  0.019 psec t- = 1.695  0.026  0.015 psec proof of principle: resolution function under control.

  19. Lifetimes results summary • Belle and BaBar now dominate world averages • Improvement by x2 over pre B-factory era • Order 1% uncertainty on lifetimes and ratio

  20. Adding Tagging Information Amix(t) (30 fb-1) Dmd = 0.516  0.016  0.010 ps -1

  21. Event samples ~1600 KS events ~500 KL signal events 60% purity

  22. Δt distributions and asymmetries CP=+1 CP=-1 B0→J/ψKL B0→J/ψKS

  23. Δt distributions and asymmetries

  24. Summary of sin2b in b  ccs already a precise measurement: 7.5%

  25. , f rarer B decays Cabbibo supressed B0→ J/yp0 B →f KS B →h‘ KS • Sensitive to new physics: • smaller amplitudes, NP through interf. terms • virtual particles (SUSY?) in penguin loops Same CKM structure as B0→J/ψKS expect S=sin2β to 5% not theoretically clean smaller rates, higher back.

  26. C = 0 if no penguin S = - sin2β if no penguin B0→ J/yp0

  27. Measuring β in b→sss

  28. Theoretical especulations • sin(2β) = SϕK=-0.39 +- 0.41 (2.7 σ) from the SM prediction; • models from SUSY could explain this result! G.L. Kane et al., PRL Apr.2003 Grossman et al. hep-ph/0303171

  29. SM is alive and well! Confidence levels in the large (rhobar,etabar) plane obtained from the global fit. The constraint from the WA sin2beta (from psi Ks modes) is included in the fit. Confidence levels in the large (rhobar,etabar) plane obtained from the global fit. The constraint from the WA sin2beta (from psi Ks modes) is overlaid.

  30. 2007 • More data close to theory limit from penguin pollution; • Measurement of ΔmS improve |Vtd/Vcb| from near cancellation of Bd and Bs form factor; • More data from B→hulν and B→hcX together with improvement in theory will give some improvement in |Vtd/Vcb| ;

  31. 1 yr LHCb 2007 now Bdpp BdJ/yKS BsJ/yf BsDsK Strategy: new physics! Goal: Physics beyond the Standard model statistics!! • Measurements which provide a • reference case for SM effects; • Compare this to channels that • might be affected by New Physics; • Understand experimental and • theoretical systematics to a level • where we can draw conclusions.

  32. for larger the B boost increses rapidly Hadronic b production B hadrons at Tevatron • b quark pair produced preferentially at low  • highly correlated tagging low pt cuts

  33. LHCb Experiment • Dedicated B physics Experiment at the LHC • pp collisions at 14TeV Muon System Z ~ 15.0-20.0 m • Acceptance : • 15-300mrad (bending) • 15-250mrad (non-bending) • Particle ID • RICH detectors • Calorimeters • Muon Detectors RICH2 Z ~ 9.5-11.9 m Calorimeters Z ~ 12.5-15.0 m RICH1 Z ~ 1.0-2.2 m

  34. One event!

  35. Tracking performance Average efficiency = 92 % Efficiency for p>5GeV >95% Momentum resolution: Dp/p=0.38% Ghost rate pT>0.5 GeV~ 7%. <N> = 27 tracks/event Mass resolution (~13 MeV) Proper time resolution (42 fs) for the decay channel Bs Dsp+ Ds KKπ

  36. No RICH With RICH Hadron ID : Physics Performance • RICH essential for hadronic decays • Example :BsK+K- • Sensitive to CKM angle  • Signal Purity improved from 13% to 84% with RICH • Signal Efficiency 79%

  37. Muon Identification Muons selected by searching for muon stations hits compatible with reconstructed track extrapolations • Compare track slopes and distance of muon station hits from track extrapolation For P>3GeV/c eff = 96.7  0.2 % misid = 2.50  0.04 %

  38. BTeV detector

  39. Calorimetry Important final states with and • Use 2x11,850 lead-tungsten crystals (PbWO4) • technology developed for LHC by CMS • radiation hard • fast scintillation (99% of light in <100 ns) Excellent energy, angular resolution and photon efficiency

  40. Strategies for measurements of CKM angles and rare decays Rare

  41. “gold-plated” decay channel at B-factories for measuring the Bd- Bd mixing phase • needed for extracting γ from Bdππand Bs  K K • in SM Adir=0, non-vanishing value (~0.01) could be a signal of Physics Beyond SM • precision measurement important Measuring β ACP(t) Inputs: 220 k/year signal 194 k/year back. Amix=sin(2β)=0.73 Adir = 0 ps

  42. Systematic errors in CP measurements • ratios • robust asymmetries high statistical precision • tagging efficiencies • production asymmetries • final state acceptance • mistag rate Control channels CP eigenstates Detector cross-checks Monte Carlo

  43. from Bs J/ψϕ • “gold-plated” decay channel for hadron machines, measuring the Bs- Bs phase • in SM expected to be ~0.03 • large CP asymmetry would signal Physics Beyond SM • also needed for extracting from Bs →ππand Bs  K K, or from Bs  Ds K • J/ψϕis not a pure CP eigenstate • 2 CP even, 1 CP odd amplitudes contributing • need to fit angular distributions of decay final states as function of proper time • requires very good proper time resolution with input values: εtag= 30% , ωtag= 30% , Δms=20/ps = 1.5 ps , , A = sin(-) = 0.03 σt = 38 fs in 1 year:σ 3.50

  44. Measuring a Using Borp  p+p-po • A Dalitz Plot analysisgives both sin(2a) and cos(2a)(Snyder & Quinn) • Measured branching ratios are: • B(B-rop-) = ~10-5 • B(Bor-p+ + r+p-) = ~3x10-5 • B(Boropo) <0.5x10-5 • Snyder & Quinn showed that 1000-2000 tagged events are sufficient • Not easy to measure • p0 reconstruction • Not easy to analyze • 9 parameter likelihood fit

  45. Measuring a Using Borp  p+p-po • Based 9.9x106 background events • Bor+p- 5400 events, S/B = 4.1 • Boropo 780 events, S/B = 0.3 Depending of assumptions on background and value of α : (from K. Honscheid)

  46. with Bd →ππ, Bs→KK • relies on “U-spin” symmetry assumption (ds), which is the only source of theoretical uncertainty • determination of and test of U-spin symmetry using measurements of from Bs J/ψϕ and β from B J/ψ KS • sensitive to New Physics contribution by comparing with obtained from Bs Ds K sensitivity in 1 year BS K K B  

  47. d,(d’,’)parametrize P over T amplitude ratio • from BdJ/ψ KS , from Bs  J/ψϕ • exact U-spin symmetry =>d = d’ ; = ’ • 3 unknowns and 4 measurements 1 year 2 years 3 years 4 years with Bd →ππ, Bs→KK 95% confidence region for d and  σγafter 4 years: 2.2º (for  = ~60º)

  48. SM : BR ~ • observation of the decay • measurement of its BR Rare B decays In the SM: Excellent probe of indirect effects of new physics! • flavour changing neutral currents • only at loop level • very small BR ~ or smaller l+l- , LHCb : 2 fb-1 ~ 33 signal events ~ 10 events background σM = 38 MeV CMS : 100 fb-1 (107s at 1034 cm-2s-1) ~ 26 signal events 6.4 events background

  49. Rare B decays A. Ali et al., Phys. Rev. D61 074024 (2000) Forward-backward asymmetry can be calculated in SM and other models BTeV data compared to Burdman et al calculation

  50. Conclusions CP violation is a cool research topic!! B factories established CP violation in the B sector and are making interesting measurements; LHCb and BTeV are second generation beauty CP violation experiments; They are well prepared to make crucial measurements in flavour physics with huge amount of statistics; Impressive number of different strategies for measurements of SMparameters and search of New Physics; Exciting times: understanding the origin of CP violation in the SM and beyond.

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