The Observation of B 0 s Oscillations at the Tevatron

1. The Observation of B0s Oscillations at the Tevatron Matthew Jones Purdue University/CDF CIPANP06

2. Fermion Masses • Gauge sector with massless fermions: • Higgs sector: • General Higgs-quark couplings: • Spontaneous symmetry breaking: diagonalize

3. CKM Sector of the Standard Model • One of several explanations for CP violation observed in • If this was the source of CP violation in the kaon system, then large effects should be observed in B decays.

4. The CKM Matrix • Unitary 3x3 matrix  4 parameters: • λ = 0.2272±0.0010 A = 0.809±0.014 • CP violation  η≠0 • Need a precise determination of Vtd Magnitude proportional to the area of this little square... Already well measured (most recent results from CKMFitter)

5. The Unitary Triangle (ρ,η) • Try to over-constrain its shape: • ACP in B0J/ψK0S: sin 2β=0.72±0.02 • Length of one side from • Length of other side from Δmd/Δms... a  b (0,0) (1,0)

6. a  b (0,0) (1,0) Last Year’s Unitary Triangle • Next strong constraint will come from Δms.

7. Mixing • Quark flavor eigenstates: • Time dependence: • CP eigenstates: • Mass difference: Δm = MH – M L

8. Time Evolution • QCD produces flavor eigenstates: • Interference between CP eigenstates • Decay identifies final quark flavor: • Fit for Δms using this model, taking into account several experimental limitations.

9. Mixing Δmd and masses are well measured From lattice QCD (hep-lat/0510113)

10. Contributions from New Physics? • FCNC suppressed in Standard Model • Contribution from new physics scenarios: • Also affects

11. Search for Bs Oscillations • Four steps: • Reconstruct decays • Measure proper decay time precisely • Identify initial flavor state • Is the data consistent with oscillations at a given mixing frequency? • Significance of an observation: Statistical power reduced by efficiency and mistag fraction (εD2)

12. (2003) Amplitude Scans and Likelihood Significance from depth of log-likelihood ratio Expect A=1 at true Δms

13. Result from the DØ Experiment • March 12, Moriond EW 2006 • Result from DØ: 17<Δms<21 ps-1 (90% CL)

14. Result from the DØ Experiment • March 12, Moriond EW 2006 • Result from DØ: 17<Δms<21 ps-1 (90% CL)

15. The CDF Detector Muon systems: CMP CMX CMU Hadronic EM Calorimeter TOF SVX-II COT

16. Signal Reconstruction • Trigger on displaced tracks and look for: 3,700 fully reconstructed 53,000 partially reconstructed

17. Limited number of patterns Cut at |d0|>120 μm Proper Decay Time • Proper decay time: ct = Lxy M/pT • Impact parameter trigger  lifetime bias • Efficiency calculated using B Monte Carlo and an emulation of the trigger • Checked using B+J/ψK+ lifetime resolution

18. Lifetime Measurements Still dominated by statistical uncertainty World Averages: hep-ex/0603003

19. Two techniques used: Opposite Side Tag QCD produces pairs Look for decay products of the other B hadron (eg, leptons) Combined effectiveness: εD2 = 1.5% Same Side Tag Initial State Flavor Tagging π Ds Same Side D decay B decay primary vertex Opposite Side Other B decay

20. Cross Checks with B0/B± Δmd=0.503±0.065 ps-1 (hadronic) Δmd=0.497±0.032 ps-1 (semi-leptonic) Δmd=0.507±0.004 ps-1 (World average) • Account for any difference between signal and calibration samples.

21. Two techniques used: Opposite Side Tag QCD produces pairs Look for decay products of the other B hadron (eg, leptons) Combined effectiveness: εD2 = 1.5% Same Side Tag Look for particles produced in association with the Bs Initial State Flavor Tagging π Ds Same Side D decay B decay primary vertex Opposite Side Other B decay

22. Same Side Kaon Tag • Local quark flavor conservation in QCD • Expect more kaons with Bs mesons • Kaon charge identifies the initial Bs flavor • A primary motivation for building TOF detector. Original estimates based on Pythia (Lund string model):

23. CDF Run II Preliminary K± around Bs K± around B0/B± CDF Data Pythia Monte Carlo Same Side Kaon Tag • Count charged kaonsaround B0, B+, Bs: • Find more kaons produced in association with Bs • Qualitative agreement with Monte Carlo

24. An Exciting Spring: • March 12: DØ result released at Moriond • March 14: CDF unblinded an analysis of about 1/3 of the hadronic decay data • Observed evidence for oscillations • Next few weeks: • Validation of remaining data • Inclusion of semi-leptonic analysis • Establish criteria for quoting a limit or a measurement

25. Unblinded CDF Analysis evidence of oscillations Released April 11, presented at FPCP 2006 on April 12.

26. Limit or Measurement? • Probability of statistical fluctuation: 0.5% • Measure -6.06

27. Constraints on CKM matrix

28. (3.8%) Future Prospects • Already limited by input from Lattice QCD • Contributes 2.9% to ξ From JLQCD Collab. (hep-ph/0307039)

29. Lattice Input from HPQCD+MILC hep-lat/0507015 mq/ms=0.036 All other uncertainties Statistical uncertainty and extrapolation to small mq/ms

30. Constraints on New Physics • Several different assumptions about flavor structure of SUSY models • Parameters in some models are constrained • Others are not... • Correlated with other experimental results on FCNC

31. Example: Impact on MFV Scenarios (2006 CDF result) (destructive ±/W± interference) Theory error on 10 Lunghi, Porod, Vives: hep-ph/0605177

32. Summary • Unlikely to be a statistical fluctuation • Next improvements from lattice results... • Long term future uncertainty: ~1%? • A milestone has been reached in the world-wide heavy flavor physics program! • But there are still many more measured to few % at CLEO-c and BES-III

33. Backup Material

34. Fully Reconstructed Bs Yields in 1 fb-1 • All decays contribute but ones with larger S/B contribute more

35. Semi-leptonic Lifetimes • Correct for unreconstructed momentum

36. Lepton-Ds Mass Distribution

37. Lifetime Resolution • Measure σct using “prompt B0s” decays: π+ φK+K- prompt track prompt Ds error propagation scale factor

38. Estimate σ*ct using event-by-event error propagation Apply scale factor Resolution is still small compared with expected period of oscillations (100 μm) Lifetime Resolution (for Δms = 18 ps-1)

39. Systematic Uncertainties on the Amplitude Hadronic Semi-leptonic • Small compared with statistical uncertainty

40. Systematic Uncertainty on Δms • Many ways to bias amplitude • Much harder to bias Δms

41. |Vtd| / |Vts| via Penguin Decays • Compare Br(Bρ) with Br(BK*) • Small branching fractions • Recent result from Belle (hep-ex/0506079): ,s ,Vts*

42. B+ produced in association with π- or K- B0 produced in association with π- or K+ Particle identification improves same side tag for B0 sample Agrees with Monte Carlo Kaons affect SST on B0/B+

43. Flavor Tagging Performance • Rank opposite side tags (no correlations) • Assume same-side and opposite-side are uncorrelated  compute combined Opposite side tags (stat. error) Same side (syst. error)

44. Dilution Scale Factor Analysis

45. Same Side Kaon Tag • Count K±, π±, p/p around B0, B+, Bs: • Find more kaons produced in association with Bs • Qualitative agreement with Monte Carlo

46. Compare predicted dilution on B+ and B0 samples Combine TOF+dE/dx Re-weight Monte Carlo to assess impact of: production mechanisms fragmentation functions observed K/π around B P-wave B mesons TOF + dE/dx modeling Luminosity dependence Same Side Kaon Tag

47. Constraints on New Physics • In context of Minimal Flavor Violation scenarios, limited by theory uncertainty • Some constraints when considering single mass insertion parameters • Weaker constraints with multiple mass insertions • These are only a few examples... see also • Carena, et al.: hep-ph/0603106 • Ball & Fleischer: hep-ph/0604249 • But there are many others Lunghi, Porod, Vives: hep-ph/0605177 Foster, Okumura, Roszkowski: hep-ph/0604121

48. GFM Single Mass Insertion Parameters Foster, Okumura, Roszkowski: hep-ph/0604121