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B s  D s - p + Mixing at CDF

LPNHE Paris. B s  D s - p + Mixing at CDF. Jónatan Piedra. September 7 2005 The Third Generation as a Probe for New Physics Experimental and Technological Approach Corfu, Greece. Outline. B s Mixing Analysis Components Absolute Dilution Calibration

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B s  D s - p + Mixing at CDF

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  1. LPNHE Paris Bs Ds-p+ Mixing at CDF Jónatan Piedra September 7 2005 The Third Generation as a Probe for New Physics Experimental and Technological Approach Corfu, Greece

  2. Outline • Bs Mixing • Analysis Components • Absolute Dilution Calibration • Dmd and Dms Amplitude Analysis • Results & Conclusions Jónatan Piedra

  3. Bs Mixing • In the SM transitions between the two Bd,s flavor eigenstates are caused by fourth order flavor-changing weak interactions • The relationship between Dmd,sand Vtd,s (CKM matrix elements) is • Bd,s oscillations are also a probe for New Physics

  4. Roadmap for Dms in Bs0 Ds-p+ Dms challenge, fast oscillations fit directly Dms is not yet possible Dmd = 0.5 ps-1 Dms 14.4 ps-1 improve world average limit event-by-event dilution amplitude scan normalization of Opposite Side Flavor Taggers dilution in samples similar to the Bs0 dilution scale factorsSD dilution calibration sample  Bs0 analysis sample dilution calibration of Opposite Side Taggers ct in ct-biased sample Di-Muon Trigger Two-Track Trigger Lepton-Track Trigger

  5. Ingredients Opposite Side Trigger Side

  6. 1. Opposite Side Trigger Side 1. Final State Reconstruction B signals from two-track and di-muon triggers

  7. Fully Reconstructed Decays • no neutrino, much better ct resolution • smaller yield than semileptonic decays

  8. Online Selection

  9. Offline Selection cut values obtained by optimizing Online and offline cuts in d0 and Lxy bias ct distribution of Dp decay modes

  10. Yields for L 355 pb-1 5300 5600 526  33 2200 115  18 6200 254  21 calibration sample Bs sample

  11. 2. Opposite Side Trigger Side 2. Proper Decay-Length Sct determined in J/ K SVT+cuts modify ct distribution in Dp

  12. Lifetime Likelihood • Use unbinned maximum likelihood fitting method • Pi is the Probability Density Function of the event i • S = true signal and misreconstructed b-hadron decays • B = combinatorial background • LctS for B  J/ K and B  Dp decay modes • Sct accounts for the underestimation of the ct resolution efficiency curve

  13. Decay-Length Efficiency Curve • SVT trigger and selection cuts sculpt the proper decay-length distribution of B  D decays • Correct with an efficiency function (ct) determined in MC

  14. Lifetime Results PDG B+ 501  5 lifetime Bd0 461  4 [mm] Bs0 438  17 lifetime [mm] 489  8 lifetime [mm] 494  11 456  27 459  11 465  39 457  10 413  56 calibration sample Bs sample

  15. 3a. Opposite Side Trigger Side 3. b-Flavor Tagging Parameterize dilution in lepton+track sample Absolute calibration in fully reconstructed Bu,d

  16. b-Flavor Tagging • A flavor tagger determines the b-flavor at production time • b quark pair production  tagging on the Trigger Side or the Opposite Side Trigger Side Opposite Side

  17. Tagging Definitions • A flavor tagger not always can be applied • It can give a wrong answer. The dilution D is a measurement of the purity of the tagger  a random (perfect) tagger has D= 0 (1) • The measured oscillation amplitude comes attenuated by D • The error on the measured amplitude depends on eD2

  18. Tagging Strategy • The Opposite Side Taggers are calibrated in the lepton+track sample • rich inclusive B meson sample • sign of the trigger lepton  decay b-flavor • The amplitude analysis needs as input an event-by-event dilution • Parameterize dilution as a function of relevant characteristics of the event The absolute dilution calibration is obtained from Bd,u J/, Dp

  19. 3b. Opposite Side Trigger Side 3. b-Flavor Tagging Parameterize dilution in lepton+track sample Absolute calibration in fully reconstructed Bu,d

  20. New likelihood • Additional input variables per event • tag decision = 0, 1 • Dilution • Additional fit parameters, related to flavor taggers • e, eB, SD, DB, Dmd • The mass PDFs remain unchanged • The decay-length PDF is different for B+ and Bd0

  21. Scale Factors Results tagger SD SMT 0.83 ± 0.10± 0.03 SET 0.79 ± 0.14± 0.04 JVX 0.78 ± 0.19± 0.05 JJP 0.76 ± 0.21± 0.03 JPT 1.35 ± 0.26± 0.02 0.85 ± 0.07± 0.01 Dmd [ps-1] CDF 0.503 ± 0.063 ± 0.015 PDG 0.510 ± 0.005 First error is statistical, second error is systematic

  22. 4. 4. Amplitude Scan for Bs Mixing Opposite Side Trigger Side

  23. Amplitude Scan on Dmd • Add an amplitude A in the likelihood, • Fit A for different values of Dm, obtaining A(Dm) and sA(Dm) • With flavor taggers calibrated, A = 1for the true mixing frequency • Exclude at 95% CL A(Dm) + 1.645sA(Dm) < 1 • Test with a simultaneous amplitude • scan of Bd D_ + and Bd J/ K*0 • A = 1 around Dmd = 0.5 ps-1 • A ~ 0 away from Dmd = 0.5 ps-1 • Compare with fit for Dmd (blue band)

  24. Amplitude Scan on Dms • Measured sensitivity, 1.645sA(Dms = 0.4 ps-1) = 1 • 95% CL limit, 0.0 ps-1 • Semileptonic + hadronic • Sensitivity • 7.4 g 8.4 ps-15.1 ps-1 in Run I • 95% CL limit • 7.7 g 7.9 ps-16.0 ps-1 in Run I • Analytical significance

  25. Results The Dms world average limit is Dms> 14.4 ps-1@ 95% CL 14.4 ps-1+ CDF II The Dms world average sensitivity is 18.5 ps-118.2 ps-1+ CDF II • Lifetime / mixing measurements in ct-biased samples • Amplitude scan performed on Bs Ds p and Bs Ds ln • Absolute calibration of the Opposite Side Flavor Taggers • Results presented at Winter Conferences • Measure Δms if close to 20 ps-1 Conclusions

  26. In Progress • Repeat Bs mixing analysis for Bs Ds p • Use SST in absolute dilution calibration • 6 additional channels in absolute dilution calibration • Perform Bs mixing analysis forBs Ds ln in TTT • Two-Track Trigger provides larger yield than lepton+SVT • New Jet Charge Tagger (NeuroBayes!) • Aim for a new Dms limit at PANIC05 (October 2005) Jónatan Piedra

  27. Back Up Slides Jónatan Piedra

  28. Why B Physics? • Improves the Standard Model (SM) knowledge by constraining CKM matrix elements • New Physics probe, by additional contributions in tree/loop diagrams • Rare decays in the SM (tree-level suppressed) • Penguin decays of B mesons • Bs0 mixing • We observe hadrons, not free quarks • Strong interaction is non-perturbative at low energy scale • Validation of theoretical methods applied on non-perturbative calculations • Measurement of masses and lifetimes • QCD probe at low energy scale

  29. Why B Physics at Tevatron? • Production rates are orders of magnitude higher than at e+e-  (4S) • Tevatron s(bb) ~ 100 mb (10 kHz, L~ 1032) • s(B+, |y|< 1, pT > 6) ~ 3 mb(300 Hz, L~ 1032) • (4S) s(bb) ~ 1 nb (5 Hz, L~ 5 x 1033) • Heavy hadron states produced (unlike B factories) • Bu, Bd0, Bs0, Lb0, Bc, b • Proton-antiproton collision  parton energy is unknown • The other b-hadron is often out of the fiducial volume • Contamination from the underlying event • Backgrounds are 3 orders of magnitude higher • Huge inelastic cross section ~ 100 mb 1 B decay ~ 103 QCD A dedicated selective trigger is needed - efficiency < O(1%)

  30. The CDF II Detector Inherited from Run I • 1.4 T Solenoid Partially new • Muon system (up to || ~ 1.5) New • Tracking System • Silicon Tracker (up to || ~ 2) • Faster Drift Chamber • Time-of-Flight (particle ID) • DAQ system, front end electronics • Trigger system (new trigger on displaced vertices)

  31. Sample Composition • partially reconstructed b-hadrons • decays with particles lost by the tracking • Normalization from real data • Shape from Monte Carlo • misreconstructed b-hadrons • when a particle has been wrongly identified • Normalization from real data • Shape from Monte Carlo • combinatorial background • at least one track isn’t from a b-hadron decay • Determined with real data signal

  32. Dilution PDF • LDS,B(D) is the PDF of observing a signal,background event with dilution D • LDS,B(D) is based on theD parameterization from the lepton+track sample for each Opposite Side Flavor Tagger two histograms are filled • Signal histograms are obtained by sideband subtraction • The histograms have not smooth shapes  no parameterization attempt

  33. D and CDF II • D • 610 pb-1 (all available up to June 2005) • Bs Ds ln, withDsp and Ds K*K • 95% CL limit = 7.3 ps-1, sensitivity 9.5 ps-1 • D and CDF II • 95% CL limit = 8.2 ps-1, sensitivity 12.2 ps-1 • Comparable to the best single measurement Jónatan Piedra

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