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B d and B s mixing at D Ø

B d and B s mixing at D Ø. BEAUTY 2005, Assisi, Perugia Tania Moulik , University of Kansas (For the DØ Collaboration). Outline. Introduction Data taking, Triggers Bd mixing measurement Reconstruction Flavor Tagging Bs mixing measurement Decay modes Amplitude scan

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B d and B s mixing at D Ø

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  1. Bd and Bs mixing at DØ BEAUTY 2005, Assisi, Perugia Tania Moulik, University of Kansas (For the DØ Collaboration) Beauty 2005, Tania Moulik (KU)

  2. Outline • Introduction • Data taking, Triggers • Bd mixing measurement • Reconstruction • Flavor Tagging • Bs mixing measurement • Decay modes • Amplitude scan • Sensitivity studies. Beauty 2005, Tania Moulik (KU)

  3. Introduction • Oscillations in the B0-B0 system first observed by ARGUS in 1987 (18 years since then!) • Signalled a large top mass • CP violation in B decays. • Many measurements on Bd mixing – LEP, SLD, CDF, DØ, Belle, Babar • Tevatron has unique opportunity to measure Bs mixing in 2 complementary analyses. Dms (This talk) and DGs/Gs (Alberto Sanchez’s talk) Beauty 2005, Tania Moulik (KU)

  4. Bd and Bs Mixing • B mixing implies a B0 transition to B0 (second order weak interactions) • Light and heavy B meson mass eigenstates differ from flavor eigenstates: Vtb Vtb t Vtb Vtb b b W b b W W t t d(s) d(s) d(s) Vtd t Vtd(s) d(s) Vtd W Vtd(s) Time evolution follows the Schrodinger equation Beauty 2005, Tania Moulik (KU)

  5. Bd, Bs mixing • The case with DG0, mixed and unmixed decay probabilities become, • Extract mixing parameter Dm from asymmetry Time evolution of B0 and B0 states, Beauty 2005, Tania Moulik (KU)

  6. Ultimate Goal – Constraing the CKM matrix - complex phase in the CKM matrix (CP violation). Wolfenstein parametrisation - expansion in l ~ 0.22 complex Beauty 2005, Tania Moulik (KU)

  7. (r,h) a g b (1,0) Dmd, Dms, and CKM x2 (x = 1.24 0.040.06) Beauty 2005, Tania Moulik (KU)

  8. Data Taking 1.8 TeV 1.96 TeV 460 pb-1 200 pb-1 Data taking e = 80 - 88% Beauty 2005, Tania Moulik (KU)

  9. m n K Ds K Bs B physics triggers p • Single muon  Muon + track match at Level 1 and a muon at L2 • Unbiased single muon triggers(PT>3,4,5) – Bd and Bs mixing, prescaled or turned off depending on luminosity. • Impact parameter biased triggers – Hadronic decays (Not being used yet). Muon system  Layers of drift chambers and scintillators. Trigger (B mixing)  Single inclusive muon trigger with |h |< 2.0, PT > 3,4,5 GeV, Dimuon trigger (second muon for tagging) Toroid Beauty 2005, Tania Moulik (KU)

  10. High statistics sample m- determines charge of the B on reconstruction side. Flavor tagging – determine charge of opposite B Sample composition – Other B decays contribute to the same final state. Validate flavor tagging to be used for main analysis, Bs mixing. n b c D0 (D*) B-(B0) u(d) u(d) Bd mixing – Motivation and Main ingredients m- W D0 K p, D*  D0ps Beauty 2005, Tania Moulik (KU)

  11. D0 and B+ selection 92 K total in 200 pb-1 • D0 selection: • 2 tracks, opposite charge, • Pt>0.7, |h|<2.0 • Displaced vertex: • d0/s(d0) of tracks > 2 • Lxy/s(lxy) > 4, • cos(a)> 0.9 • Good vertex fit. • D0m (B+) selection: • If lxyB/s(lxyB) > 4, then cos(aB ) > 0.95 • lxyB < lxyD within 3s • Does not form a D* with a soft pion. Beauty 2005, Tania Moulik (KU)

  12. B vertex Primary vtx X Lxy Bd mixing measurement • Fit the c2 in VPDL bins to extract Dm and purity of tag Measured Expected PT(B) Visible Proper Decay Length: Charge of B determined from m charge on reconstructed side Opposite B charge from Flavor Tag Beauty 2005, Tania Moulik (KU)

  13. Expected Asymmetry • Distribution of oscillated and non-oscillated events are function of K-factor,h, Dm • B not fully reconstructed. Measure average k-factor K = Pt(mD0)/Pt(B) K-factor Reconstruction efficiency of jth channel VPDL resolution Beauty 2005, Tania Moulik (KU)

  14. Bd mixing – Decay length resolution 793 K readout channels F-Disks Barrel H-disks • 6 Barrels – 4 layers, Double sided except for layers 1 and 3 of the outermost barrels. • Interspersed F disks – double sided • H disks – single sided, 24 wedges per h-disk 22.1+-1.7mm 50.5+-3.1mm Beauty 2005, Tania Moulik (KU)

  15. Flavor Tagging ----We have explored --- Jet charge, Soft muon, Same side tagging Beauty 2005, Tania Moulik (KU)

  16. Flavor tagging merit (eD2) Flavor Tagging Definitions Same side Tagging B meson PB+Ptrk Jet Charge Ptrel Candidate track Ptrk Beauty 2005, Tania Moulik (KU)

  17. Fitted asymmetry • Simultaneous fit to D* and D0 sample to extract Dm. Muon Tagger B+D0m X JetQ+SST Dm = 0.4560.0340.025 ps-1 (D*) – Bd contribution ~83% (D0) – B+ contribution ~76% Beauty 2005, Tania Moulik (KU)

  18. Bs Mixing • Very similar analysis to the Bd mixing. Decay mode used: Bs  Ds m n, Dsfp, fK+K- 675±43 133329277 Beauty 2005, Tania Moulik (KU)

  19. For…Bs mixing observation S = signal events eD2 = tagging power S/B = signal/background st = proper time resolution Beauty 2005, Tania Moulik (KU)

  20. b Significant Improvements to flavor tagging Add Secondary Vertex Charge Tagging Likelihood ratios for variables discriminating between b and b  ptrel.q, svcharge,jetcharge Normalized Tagging variable d  Monotonic function between (-1,1) d>0 (b) , d<0(b) Beauty 2005, Tania Moulik (KU)

  21. “Proof of principle” – Dmd measurement Dmd = 0.558+-0.048(stat.) ps-1 eD2 = 1.0% (OST Tagging only) Beauty 2005, Tania Moulik (KU)

  22. Bs mixing limit – Amplitude fit method Ideal non-osc/osc number of events as a function of VPDL (x)  Fit for Amplitude A Fit for A as a function of Dms ( in steps of 1 ps-1) Beauty 2005, Tania Moulik (KU)

  23. Impact parameter resolution and tuning. Variable scale factor for VPDL resolution (s.s)– Overall scale factor = 1.10 Tune track errors for data and MC taking taking into account dependence on: • Track momentum • Track angles • Silicon detector hit configuration • Silicon cluster width Beauty 2005, Tania Moulik (KU)

  24. Sample composition Beauty 2005, Tania Moulik (KU)

  25. Bs mixing Limit (460 pb-1) • Expect A=1, for freq = trueDms, A=0 for freq trueDms • 95% C.L • smallest value of Dms at which, A+1.645sA = 1 • Sensitivity: • Dms value with1.645sA = 1 Dms > 5.0 ps-1 Sensitivity = 4.6 ps-1 Beauty 2005, Tania Moulik (KU)

  26. To be Added… • Reconstructed candidates = 4933 376 Beauty 2005, Tania Moulik (KU)

  27. World averages for Dmd world Bs mixing limit Dms > 14.5 ps-1 Sensitivity = 18.2 ps-1 0.5020.006 ps-1 Beauty 2005, Tania Moulik (KU)

  28. Future Perspectives With additional Channels and Improvements In flavor tagging Dms upto 11 ps-1 Within reach at 3.5 fb-1 Beauty 2005, Tania Moulik (KU)

  29. Future perspectives With increase in bandwidth Dms upto 18 ps-1 Addition of hadronic decay Modes and Layer0 + 50 Hz Bandwidth Dms upto 26 ps-1 Beauty 2005, Tania Moulik (KU)

  30. Conclusions and Summary • Bd mixing measurement • We can contribute to the Bd mixing measurement in a small way and an important cross check of the measurement in a hadron collider environment. It is mainly important as a validation tool for our flavor tagging. • Bs mixing measurement • More statistics • Improvements in flavor tagging, introduction of electron tagging (Almost ready!), Unbinned likelihood fit • More decay modes, • BsD s e n X • Addition of Ds  K*K • Addition of hadronic decay modes • Addition of Layer0  improvements in impact parameter resolution • We are excited…. Lots more to come…. Beauty 2005, Tania Moulik (KU)

  31. BACKUP Beauty 2005, Tania Moulik (KU)

  32. Inner Tracker Beauty 2005, Tania Moulik (KU)

  33. D0 Silicon – RunIIa disks Beauty 2005, Tania Moulik (KU)

  34. Silicon Alignment Beauty 2005, Tania Moulik (KU)

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