1. CP Violation: Recent Measurements and Perspectives for Dedicated Experiments LAFEX/CBPF March, 2001 Outline Introduction CP violation in the B sector BaBar and Belle Future experiments: BTeV and LHCb Strategies to measure the CP viol. parameters Conclusions João R. T. de Mello Neto Instituto de Física

2. SM with 3 generations and the CKM ansatz can accomodate CP CP is one of the less experimentally constrained parts of SM 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 Motivations CP violation is one of the fundamental phenomena in particle physics CP asymmetries in the B system are expected to be large.

3. The symmetry, or invariance, of the physical laws describing a system undergoing some operation is one of the most important concepts in physics. Symmetries are closely linked to the dynamics of the system Different classes of symmetries: Symmetry in Physics Translation in Space Translation in Time Rotation in Space Lorentz Transformation Reflection of Space (P) Charge Conjugation (C) Reversal of Time (T) Interchange of Identical Particles Gauge Transformations Examples of Symmetry Operations Lagrangian invariant under an operation limits the possible functional form it can take. continuous X discrete, global X local, etc.

4. Three Discrete Symmetries Parity, P x   xL  L Charge Conjugation, C e   e  K   K   Time Reversal, T t  t CPT Theorem –One of the most important and generally valid theorems in quantum field theory. –All interactions are invariant under combined C, P and T –Only assumptions are local interactions which are Lorentz invariant, and Pauli spin-statistics theorem –Implies particle and anti-particle have equal masses and lifetimes  

5. Current understanding of Matter: The Standard Model Quarks Leptons Three generations of fermions Q = +2/3 Q = -1/3 Q = -1 Q = 0 Interactions (bosons) Z W g (QED) Weak Strong Eletroweak (QCD) HHiggs Very successful when compared to experimental data! especified by gauge symmetries SU(3) C  SU(2) L  U(1) Y

6. SM at work neutral currents, charm, W and Z bosons;

7. Weak Interactions can change the flavour of leptons and quarks b WW c gV cb ee WW e g g: universal weak coupling matrix rotates the quark states from a basis in which they are mass eigenstates to one in which they are weak eigenstates V CKM : 3  3 complex unitary matrix four independent parameters (3 numbers, 1 complex phase) effects due to complex phase: CP violating observables result of interference between different amplitude all CP violating observables are dependent upon one parameter

8. Despite the maximal violation of C and P symmetry, the combined operation, CP, is almost exactly conserved Symmetry and Interactions CP Symmetry and the Weak Interaction L R L R C C P P CPCP Exists Doesn’t Exist Doesn’t Exist

9. Standard Model: CKM matrix = The quark electroweak eigenstates are connected to the mass eigenstates by the CKM matrix : = mixing phase Weak decay phase mixing phase phenomenological applications: Wolfenstein parameterization

10. In SM: (0,0)     V ub   V cb  V td (,)(,) (1,0) V td V tb  +V cd V cb  +V ud V ub  = 0 Unitarity triangles V td V ud  +V ts V us  +V tb V ub  = 0  V ub   V td  V ts  

11. CP Violation in B Decays d b WW d u u d   B0B0 Decay Diagram B0B0 B0B0 b bd d u,c,tu,c,t u,c,tu,c,t WW WW Mixing Diagram In order to generate a CP violating observable, we must have interference between at least two different amplitudes B decays: two different types of amplitudes decay mixing 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 interference between mixed and unmixed decays

12. CP Violation in B Decays Direct CP Violation –Can occur in both neutral and charged B decays –Total amplitude for a decay and its CP conjugate have different magnitudes –Difficult to relate measurements to CKM matrix elements due to hadronic uncertainties –Relatively small asymmetries expected in B decays Indirect CP Violation –Only in neutral B decays –Would give rise to a charge asymmetry in semi-leptonic decays (like  in K decays) –Expected to be small in Standard Model CP Violation in the interference of mixed and unmixed decays –Typically use a final state that is a CP eigenstate (f CP ) –Large time dependent asymmetries expected in Standard Model –Asymmetries can be directly related to CKM parameters in many cases, without hadronic uncertainties B0B0 B0B0 f CP

13. CP Assymmetry in B decays To observe C P violation in the interference between mixed and unmixed decays, one can measure the time dependent asymmetry: For decays to CP eigenstates where one decay diagram dominates, this asymmetry simplifies to: Requires a time-dependent measurement Peak asymmetry is at t = 2.3   M  0.7 for B 0

14. Experimental bounds on the Unitarity Triangle B d mixing:  m d B s mixing:  m s /  m d b  ul, B  l :V ub Kaon mixing & B K decays:  K

15. B factories e + e -  (4s)  = 0.56 B 0 z CP B 0 z tag

16. Measurements of sin(2  )

17. theory well measured Measurements before 2005 Constraints from the unitarity triangle: consistency with the SM (within errors) inconsistency with the SM ( not well understood) Next generation of experiments : precise measurements in several channels constrain the CKM matrix in several ways look for New Physics theory low statistics mixing no precise/direct measurement BaBar, Belle CDF, D0 HERA-B Will establish significant evidence for CP violation in the B sector V td no access to  V ub  V cb well measured

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

19. LHC and Tevatron experiments

20. Generic experimental issues p (p) p B B triggering flavour tagging particle ID 1 cm f decay time resolution neutrals detection systematic effects

21. u Flavour tagging For a given decay channel signal B other B SS: look directly at particles accompanying the signal B OS: deduce the initial flavour of the signal meson by identifying the other b hadron b s s u semileptonic decay kaon tag jet charge

22. Flavour tagging w: wrong tag fraction  : tagging efficiency N: total untagged

23. The BTeV detector Central pixel vertex detector in dipole magnetic field (1.6 T) Each of two arms: –tracking stations (silicon strips + straws) –hadron identification by RICH –  0 detection and e identification in lead-tungsten crystal calorimeter –  triggering and identification in muon system with toroidal magnetic field Designed for luminosity 2 x 10 32 cm -2 s -1 ( 2 x 10 11 bb events per 10 7 s ) Trigger strategy (three levels) pioneering pixel vertex trigger software triggers

24. 17 silicon vertex detectors 11 tracking stations two RICH for hadron identification a normal conductor magnet (4 Tm) hadronic and eletromagnetic calorimeters muon detectors The LHCb Detector Trigger strategy (four levels) “high” p t, e,, h secondary vertex software triggers

25. Calorimetry Important final states with and Use 2x11,850 lead-tungsten crystals (PbWO 4 ) technology developed for LHC by CMS radiation hard fast scintillation (99% of light in <100 ns) Excellent energy, angular resolution and photon efficiency Pions with 10 GeV

26. Particle Id Essential for hadronic PID Aerogel flavour tag with kaons (b  c  K) background suppression two body B decay products

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

28. Penguins: expected to be small same weak phase as tree amplitude dilution factor: tagging background Standard Model: Observation of direct asymmetries (10% level): strong indication of New Physics! 80.5k 9.3 180.017 BTeV LHCb events /1y 88k  (M) / MeV/c 2 7 0.025 0.021 ATLAS165k CMS 433k160.015

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

30. experimental: background with similar topologies theoretical: penguin diagrams make it harder to interpret observables in term of BTeV LHCb events/10 7 s 23.7 k 12.3 k (MeV) 29 17 0.024 -- 0.090.07 C -- -0.49

31. CP conserving strong phase approximately 4-fold discrete ambiguity in    (degrees )  (degrees) |P/T|=0.1 0.05 0.02 1 year 5 year

32. Time dependent Dalitz plot analysis Tree terms Penguins Helicity effects: corners Cuts: lower corner eliminated Unbinned loglikelihood analysis: 9 parameters Under investigation: background Dalitz plot acceptance other resonances EW penguins BTeV LHCb events/1y cos(2  ) and sin(2  ) no ambiguity 10.8k 3.3k  (MeV) 28 503 o -6 o ~10

33. color allowed doubly Cabibbo suppressed color suppressed Cabibbo allowed comparable decay amplitudes unknows:  =65 o (1.13 rad) b=2.2x10 -6  (  )=10 o

34. four time dependent decay rates: no penguin diagrams: clean det. of two asymmetries weak phase strong phase difference between tree diagrams exclusive reconstruction ~ 83k / year S/B ~ 12 inclusive reconstruction ~ 260k / year S/B ~ 3 V ud V cb * V ub V cd * 22  V tb * * V td small asymmetry: suppressed V ub

35. uncertainty due to: ~ 360k / year requires full angular analysis addition of channel:

36. Mixing very important for flavour dynamics future hadron experiments: fully explore the B s mixing SM: flavour specific state untagged: fit proper time distributions for tagged: BTeV LHCb tagged 34.5k 72k 43fs

37. Mixing Amplitude fit method: A,  A determined for each by a ML fit

38. Theoretically clean (no pinguins) Hadron identification: background Interference of direct and mixing induced decays V us V cb * V tb * * V ts V ub V cs * amplitudes about same magnitude four rates two asymmetries

39. BTeV LHCb Sensitivity to: events/1y 13.1k 6k

40. dominated by one phase only very small CP violating effects (SM) sensitive probe for CP violating effects beyond the SM CP eigenstate direct extraction of BTeV events/1y 9.2k 0.033 (x S =40) CP admixture clean experimental signature full angular analysis LHCb CMS events 370k (5y) 600k (3y) (x S =40) 0.03

41. Sensitivity to New Physics Transversity analysis A. Dighe hep-ph/0102159 (CERN-TH/2001-034) simpler angular analysis with the transversity angle accuracy similar for same number of events if is large the advantage of is lost

42. related by U-spin symmetry makes use of penguins (sensitive to new physics...) four observables: seven unknowns: U-spin symmetry: input and contour plots in the and planes BTeV LHCb events/1y 32.9k 9.5k -- 0.034 -- d()d() (5y)

43. 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! SM : BR ~ observation of the decay measurement of its BR LHCb ATLAS CMS width MeV/c 2 signal backg 26 62 33 27 21 10 93 3 SM : BR ~ high sensitivity search measure branching ratios study decay kinematics events/1y BTeV LHCb 2.2k S/B 11 4.5k 16 (3y)

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

45. Physics summary (partial) ParameterChannels BTeV LHCb sin(2  )B d  J/  K s 0.025 0.021  B d  A(t) 0.024-- A mix --0.07 A dir --0.09 sin(2  )B d  10  3  - 6  2  +  B d  D   --> 5   -2  B s  D s K 6  -15  3  -14   B d  DK  --10  B -  D  K - 10  -- sin(2  )B s  J/  --0.03 (5y) B s  J/   0.033-- Bs oscil. x s B s  D s  (up to) 75 (up to) 75 Rare Decays B s   --11(3.3) B d  K   2.2k (0.2k) 22.4k(1.4k) Other physics topics: B c mesons, baryons, charm, tau, b production, etc

46. References CERN yellow report, Proc. of the Workshop on Standard Model Physics (and more) at the LHC, May 2000, CERN 2000-004; BTeV Proposal, May 2000; LHCb Proposal, February 98;

47. Conclusions BTeV and LHCb are second generation beauty CP violation experiments; Both are well prepared to make crucial measurements in flavour physics with huge amount of statistics; Impressive number of different strategies for measurements of SM parameters and search of New Physics; Exciting times: understanding the origin of CP violation in the SM and beyond. CP violation is one of the most active and interesting topics in today’s particle physics; The precision beauty CP measurements era already started - Belle and BaBar;