1. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 1 B s Mixing at CDF Frontiers in Contemporary Physics Nashville, May 24 2005 Gavril Giurgiu – for CDF Collaboration Carnegie Mellon University

2. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 2 Introduction - Motivation: Constrain the CKM matrix elements - Within the Standard Model, B d/s mixing provides information on V td/s - Although  m d is well measured (0.502  0.007ps -1 ) determination of V td is affected by 15% error

3. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 3 Unitarity Triangle - Unitarity of CKM matrix: - Knowledge of both B d and B s mixing frequencies would provide better constraints on one side of unitarity triangle:  =1.15  0.05 from Lattice QCD

4. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 4 Current B s Status - B s mixing not observed yet - B s oscillates more than 30 times faster than B d  experimental challenge - At 95% CL lower limit  m s > 14.4 ps -1 with sensitivity of 17.8 ps -1

5. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 5 B Mixing Phenomenology - Neutral B system: - Mass eigenstates: - Oscillation frequency of B q mesons given by  m q = M H -M L - Lifetime difference  H  L - Neglecting , mixing probability after time t is give by:

6. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 6 CDF Detector

7. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 7 CDF Detector – Schematic View Plug Calorimeter 1.3 < |  | < 3.5 Central Tracker (COT) |  | < 1.0 dE/dx for PID Time of Flight for K/p separation placed before 1.4 Tesla Solenoid Electromagnetic and Hadronic calorimeters Silicon Detector |  | < 2.0 Muon Detectors |  | < 1.0

8. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 8 Silicon Vertex Trigger (SVT) - Silicon Vertex Trigger implemented at Level 2 -Uses silicon detector information and beamline position to determine the track impact parameter -Good impact parameter resolution ~ 47  m: ~33  m beam size  ~30  m intrinsic SVT resolution -Trigger on displaced track

9. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 9 Mixing Analysis Overview - Mixing analysis ingredients: - Signal reconstruction - Decay time - B flavor at decay - B flavor at production inferred through flavor tagging: - lepton tags - jet charge tags - Statistical significance of  m s measurement: Tagging Signal Reconstruction Decay time resolution

10. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 10 SVT Triggers for B Physics Semileptonic (partially reconstructed) decays: B s  lepton D s X - large number of events - decay time resolution degraded due to missing neutrino - triggered by 4 GeV lepton and displaced track with impact parameter |d 0 |>120  m and |d 0 |<1 mm Hadronic (fully reconstructed) decays: B s   D s - smaller number of events - good decay time resolution - triggered by two displaced tracks with impact parameter |d 0 |> 120  m and |d0|<1 mm d0d0 d0d0 d0d0

11. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 11 Semileptonic B s Signals - Missing neutrino  cannot see B s mass peak - Use D s mass peak and (lepton, D s ) charge correlation: l + D - - right sign combination l - D - - wrong sign combination - Decay modes: D s    ( 4355  94 ) D s  K*K ( 1750  83 ) D s  3  ( 1573  88 ) - Total of 7000 B s candidates but ~20% come from “Physics backgrounds”: B 0/+  D s D B s  D s   (D /  D (s)  lepton X) B s  D s D (s)

12. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 12 Semileptonic B s Signals (cont) D s  K*K ( 1750  83 )D s  3  ( 1573  88 )

13. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 13 Hadronic B s Signals - All final state particles reconstructed  observe B s mass peak - Decay modes: D s    ( 526  33 ) D s  K*K ( 254  21 ) D s  3  ( 116  18 ) - Total of 900 B s candidates - Satellite peak: B s  D s *  (D s *  D s X)

14. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 14 Hadronic B s Signals (cont) D s  K*K ( 254  21 )D s  3  ( 116  18 )

15. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 15 Decay Time - Decay time: - In semileptonic modes missing neutrino is statistically corrected by: - Hadronic decays do not need correction - Decay time resolution: Hadronic: Semileptonic:

16. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 16 Decay Time Bias - Because: (1) In both hadronic and semileptonic decays the triggers require displaced tracks (2) B s events are selected based on decay distance cuts the B s decay time distribution is biased - Efficiency as function of decay time obtained from Monte Carlo:

17. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 17 Flavor Tagging - For B s mixing analysis CDF used 5 opposite side flavor taggers - Tag inferred from opposite side B in event: - muon and electron tag (semileptonic decay of opposite B) - three jet charge tag types: - displaced vertex - displaced tracks - high p T - Tagging power given by  D 2 where  is the tagging efficiency D = 1 – 2 P mistag is the tagging dilution P mistag – mistag probability - Large dilution (D) means high tagging power Trigger B meson

18. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 18 Flavor Tagging (cont) - Dependence of dilution on different quantities enhances tagging power - Dilution of lepton taggers is calculated as function of: - lepton likelihood (probability that lepton is real) - (transverse momentum of lepton w.r.t jet axis) - Dilution of jet charge tagger is calculated as function of - the jet charge: d i - displacement of track i w.r.t the primary vertex - Total  D 2  1.6 % calculated on an inclusive lepton+SVT sample Electron tagMuon tag Jet charge tag

19. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 19 Tagger Calibration and Measurement of  m d - Perform measurement of  m d - Since we observe B 0 oscillations, we can also measure tag dilutions - Analyze hadronic and semileptonic decays of B 0 and B + : B 0  D +   B +  D 0   B 0  J/  K *0 B +  J/  K + B 0 /+  D - l + X B 0 /+  D -* l + X B + /0  D 0 l + X - Event by event predicted dilution (D) - Fit the dilution calibration factor (S) for each of 5 tag types - Dilution calibration factors are used for the B s mixing analysis Event by event dilution Dilution Calibration Factor

20. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 20  m d Results - Hadronic:  m d = (0.503±0.063±0.015) ps -1 - Dilution calibration factors: S(muon) = 0.83±0.10±0.03 S(electron) = 0.79±0.14±0.04 S(vertex) = 0.78±0.19±0.05 S(track) = 0.76±0.21±0.03 S(high p T ) = 1.35±0.26±0.02 - Total  D 2 ~ 1.1% - Semileptonic:  m d = (0.498±0.028±0.015) ps -1 - Dilution calibration factors: S(muon) = 0.93±0.04±0.03 S(electron) = 0.98±0.06±0.03 S(vertex) = 0.97±0.06±0.04 S(track) = 0.90±0.08±0.05 S(high p T ) = 1.08±0.09±0.09 - Total  D 2 ~ 1.4% Muon Tags World average:  m d = 0.502  0.007 ps -1

21. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 21 Lifetime Measurement - As a cross check of analysis framework measure B s lifetime - Lifetime fit projections in both hadronic and semileptonic modes - Semileptonic: c  (B s ) = 443  10 (stat)  xxx (syst)  m - Hadronic: c  (B s ) = 479  29 (stat)  5 (syst)  m - Good agreement with PDG 2004: c  (B s ) = 438  17  m

22. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 22 Amplitude Scan Method - Introduce Fourier coefficient A (amplitude) - Fix  m at different test values and fit for A: (Moser et.al., NIMA 384 491) A  1 for true value of  m A  0 away from true value - Test amplitude method on B 0 oscillations by scanning for  m d in hadronic modes - points: A  1  - yellow band: A  1.645  - dotted line: 1.645  - Yellow band bellow 1  exclusion at 95% CL zoom in

23. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 23 B s Analysis - Performed “blind” analysis by randomizing the tag decision: tag = tag  (-1) event number - Evaluate sensitivity and systematic uncertainties from “blind” analysis - Systematic errors evaluated using pseudo-experiments: - include all variables and distributions determined from data - fit the toy sample with different Likelihood configurations - use variations in Amplitude (  A) and statistical error (  A ) to derive the systematic error:

24. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 24 Semileptonic Amplitude Scan - Measurement is statistics dominated - Main systematic uncertainties from prompt background and from Physics background Sensitivity: 7.4 ps -1 Limit:  m s > 7.7 ps -1

25. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 25 Hadronic Amplitude Scan - Measurement is statistics dominated - Main systematic errors come from tagger calibration Sensitivity: 0.4 ps -1 Limit:  m s > 0.0 ps -1

26. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 26 Combined CDF result on  m s - After combining semileptonic and hadronic modes: Sensitivity: 8.4 ps -1 Limit:  m s > 7.9 ps -1 - With full B s momentum reconstruction, hadronic mode will dominate the measurement at high  m s

27. Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 27 Conclusions  m s limits from CDF: Semileptonic: 7.4 ps -1 Hadronic: 0.0 ps -1 (will become important at high  m s with more statistics) Combined limit: 7.9 ps -1, sensitivity: 8.4 ps -1 Results will substantially improve soon: - Same side Kaon tagger - Improve decay time resolution in hadronic modes - Add more data Updated analyses expected soon