CP Violation

1. CP Violation Recent results and perspectives João R. T. de Mello Neto Instituto de Física Universidade Federal do Rio de Janeiro IF – UFRJ, July/2003

2. Outline • Introduction • CP Violation in the SM • Measurement of β • B Factories results • Other measurements • Hadron colliders (LHCb) • New physics • 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. D0 2001 BTEV ATLAS BELLE CLEO 3 1999 ? 2008 1999 Huge experimental effort Plus hundreds of experimental groups around the World.

6. Matter – antimatter oscillations ΔB=2 ordinary ΔB=1 interactions exchange of virtual q (2/3) t : dominant amplitude 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. S C General time-dependent formalism Interfering amplitudes with different CP-violating (weak) phases can give a non-zero CP asymmetry. For B0 → fCP: Then, when one of the interfering amplitudes is B-mixing with Only one decay amplitude (or all decay amp. same CKM phase): C=0 and S gives clean CKM phase information

11. Measuring β • Golden modes: • clean theory • “relatively easy” experiment • Tree and leading penguin have same phase • sinDmDt coeff. measures sin2b cleanly • Not just J/y KS: • Also y’ KS, cc1 KS, hc KS (CP=-1) • J/y KL (CP=+1) • J/y K*0 (Mixed CP)

12. Measuring β

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

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

15. Babar detector

16. 8K events 12K events Mixing and lifetimes Results based on large samples of • Fully or partially reco. hadronic decays • Fully or partially reco. D* l n • Dileptons 29 fb-1

17. Δt Distributions  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

18. 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

19. Adding Tagging Information Dmd = 0.516  0.016  0.010 ps -1 30 fb-1

20. Event samples Clean ~2K KS sample + ~ 500 KL events with ~ 60% purity 1.6K events ~500 signal ev.

21. Events with KS Events with KL Δt distributions and asymmetries CP=+1 CP=-1

22. Δt distributions and asymmetries

23. Summary of sin2b in b  ccs 7.5% precision

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

25. , f Measuring β in b→sss B →f KS B →h‘ KS • Same CKM structure • as J/ψ KS • u-penguin down by ~1/50 • Expect S=sin2β to 5% • Like ϕKS but also u-tree • Still, S~sin2b

26. Measuring β in b→sss

27. 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

28. 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.

29. 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| ;

30. 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.

31. 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

32. 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

33. One event!

34. 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+ KKπ S. Amato C. Nunes JTMN

35. 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%

36. 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 % M. Gandelman JTMN

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

38. Measuring β S. Amato C. Nunes JTMN

39. Measuring β S. Amato C. Nunes JTMN

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

41. experimental: • background with • similar topologies • theoretical: penguin diagrams make it harder to interpret • observables in term of

42. CP conserving strong phase |P/T|=0.1 0.05 0.02 approximately

43. SM : BR ~ • observation of the decay • measurement of its BR width MeV/c2 signal backg LHCb 26 33 10 Rare B decays • flavour changing neutral currents • only at loop level • very small BR ~ or smaller In the SM: Excellent probe of indirect effects of new physics! Franciole S. Amato

44. Rare B decays Forward-backward asymmetry can be calculated in SM and other models (1y) LHCb A. Ali et al., Phys. Rev. D61 074024 (2000) H. Lopes LHC Physics – Praga (B. de Paula)

45. Measuring γ Amplitudes of the charge conjugated process are obtained from the above ones just changing the signal from weak phase.

46. Measuring γ M. Gandelman K. Akiba

47. LHCb reach in one year (2 fb-1) Numbers being updated for the Physics TDR .

48. Conclusions CP violation is a cool research topic!! B factories established CP violation in the B sector and are making interesting measurements; LHCb is a second generation beauty CP violation experiment; It is 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.

49. SM is alive and being poked !