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Md. Naimuddin (on behalf of CDF and D0 collaboration) University of Delhi Recontres de Moriond

Md. Naimuddin (on behalf of CDF and D0 collaboration) University of Delhi Recontres de Moriond 19 th March, 2006. B s Mixing at the Tevatron. OUTLINE. Introduction to Mixing Why study Mixing Fermilab Tevatron Data Taking CDF and D0 Detectors Analysis strategy

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Md. Naimuddin (on behalf of CDF and D0 collaboration) University of Delhi Recontres de Moriond

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  1. Md. Naimuddin (on behalf of CDF and D0 collaboration) University of Delhi Recontres de Moriond 19th March, 2006 Bs Mixing at the Tevatron Md. Naimuddin

  2. OUTLINE • Introduction to Mixing • Why study Mixing • Fermilab Tevatron • Data Taking • CDF and D0 Detectors • Analysis strategy • Bs mixing at CDF • Bs mixing at D0 • Results and Conclusions Md. Naimuddin

  3. Introduction Mixing: The transition of neutral particle into it's anti-particle, and vice-versa First observed in the K meson system. In the B meson system, first observed in an admixture of B0 and Bs0 by UA1 and then in B0 mesons by ARGUS in 1987. These oscillations are possible because of the flavor-changing term of the Standard Model Lagrangian, Md. Naimuddin

  4. Introduction Where VCKM is the CKM matrix; Wolfenstein parametrisation- expansion in  ~ 0.22 CP violation in the Standard Model originates due to a complex phase in the CKM matrix (quark mixing). Md. Naimuddin

  5. 1 ( ) ( ) - G = G ± D e t P t 1 cos mt u , m Mixing in B mesons Light and Heavy B mesons mass eigenstates differ from flavor eigenstates: Time evolution of B0 and states In case  0, 2 Md. Naimuddin

  6. Why Bs mixing is important standard model Expectation: Δms= 14 - 28ps-1 Δmd= 0.5ps-1 measurement of Δms/Δmd  Vts/Vtd constrain unitary triangle f2BdBBd = (228+30+10 MeV)2 |Vtd| from md limited by ~15%  consider ratio Determine |Vts|/|Vtd| ~ 5% precision K mixing  direct & indirect CPV Bd mixing  heavy top mass  mixing  neutrino mass  0 Bs mixing  ???? Md. Naimuddin

  7. Fermilab Tevatron Highest Luminosity achieved: 1.7x1032 cm/s2 Expected: 2 – 3 x 1032 cm/s2 Md. Naimuddin

  8. Data Taking Excellent performance by the Tevatron and we are doubling our data set every year. Data taking efficiency is ~ 85%. Pb-1 We already have collected about 10 times of run 1 data. Md. Naimuddin

  9. CDF Detector • Solenoid 1.4T • Silicon Tracker SVX • up to |h|<2.0 • SVX fast r- readout for trigger • Drift Chamber • 96 layers in ||<1 • particle ID with dE/dx • r- readout for trigger • Time of Flight • →particle ID Md. Naimuddin

  10. D0 Detector • 2T solenoid • Fiber Tracker • 8 double layers • Silicon Detector • up to |h|~3 • forward Muon + Central Muon detectors • excellent coverage ||<2 • Robust Muon triggers. Md. Naimuddin

  11. Reconst- ruction Flavor tagging Proper time Analysis strategy • Measuring Bs oscillations is much more difficult than Bd oscillations because of the fast mixing frequency. In order to measure, We need to: Reconstruct the Bs signal. Know the flavor of the meson at it’s production time (Flavor tagging) and get D2 Proper decay length resolution Md. Naimuddin

  12. Reconst- ruction Flavor tagging Proper time • Semileptonic modes collected by the two track trigger Md. Naimuddin

  13. Reconst- ruction Flavor tagging Proper time • More than 2300 Bs signal candidates in 765 pb-1 BsDs-()+ Md. Naimuddin

  14. Reconst- ruction Flavor tagging Proper time 26,710±560 7,422±281 5,601±102 1,519±96 • Currently using only semileptonic decay of the Bs Bs Ds X (Ds) ( K+K-) Untagged Tagged Md. Naimuddin

  15. Reconst- ruction Flavor tagging b-hadron neutrino Jet charge Trigger lepton Fragmentation pion Proper time  B D PV Soft lepton Lxy e or  • Soft Lepton Tagging ( or e): • Charge of the leptons provides the flavor of b. • Jet Charge Tagging: • Sign of the weighted average charge of opposite B jet provides the • flavor of b. • Same Side(Kaon) Tagging (New at CDF) • B meson is likely to be accompanied by a close K/ • particle Id helps Opposite side Same side Md. Naimuddin

  16. Reconst- ruction Flavor tagging Proper time Opposite side Tagging: Same side Kaon Tagging: Md. Naimuddin

  17. Reconst- ruction Flavor tagging Proper time • Using only Opposite side e, , secondary vertex or jet charge for tagging Tagger tuned using Bd mixing measurement md = 0.506±0.020±0.014 ps-1 Md. Naimuddin

  18. Reconst- ruction Flavor tagging Proper time Easier to calculate for Hadronic decays Proper decay time given as : Distance from PV to SV in transverse plane Due to missing neutrino, it becomes little tricky in semileptonic sample Missing momentum  increased ct error ( ct) Proper decay time given as: Boost meson back to its rest frame where from MC Md. Naimuddin

  19. Reconst- ruction Flavor tagging Proper time Scale factor = 1.17 +/- 0.02(largest systematic) Best estimate of errors used in track fitting, any additional scaling determined from data Pull of J/y vertex from the primary vertex for prompt J/ s Md. Naimuddin

  20. Fitting procedure • Amplitude Fitting approach: • Introduce amplitude • Fit for A at different ms • Traditionally used for Bs mixing search • Easy to combine experiments • Likelihood approach: • Search for min, which minimizes the –ln(L), • where minis the estimator of the true frequency. • Difficult to combine the results from different experiments. Md. Naimuddin

  21. Amplitude fit method • Fit to data - free parameter • Obtain as a function of • Measurement of gives and otherwise • At 95% CL • sensitivity • excluded • Systematics is given by Md. Naimuddin

  22. Bs mixing limit Limit: ms > 8.6 ps-1 @ 95% confidence Sensitivity: 13.0 ps-1 @ 95% confidence Md. Naimuddin

  23. Bs mixing limit Limit: ms > 14.8 ps-1 @ 95% confidence Expected Limit: 14.1 ps-1 @ 95% confidence A clear deviation of 2.5  from 0 can be seen at ms~19 ps-1 Dominant sources of systematic uncertainty: Scale factor, K factors and Sample composition Md. Naimuddin

  24. Likelihood scan • Resolution • K-factor variation by 2% • BR (BsDsX) • ccbar contamination • BR (BsDsDs) Syetematics 17 < Dms < 21 ps-1 @ 90% CL Most probable value of Dms = 19 ps-1 Md. Naimuddin

  25. Significance Test Probability for this measurement to lie in the range 16 < Dms < 22ps-1 Given a true value: Dms > 22 ps-1: 5.0% Dms = 19 ps-1: 15% Simulate Dms = infinity by randomizing flavor tagging variable Consistent results from parameterized MC studies Md. Naimuddin

  26. CKM fit without new D0 result Md. Naimuddin

  27. CKM fit with new D0 result Disclaimer: Produced only yesterday by CKM group so I don’t have much information about the inputs. Md. Naimuddin

  28. CONCLUSIONS Limit: ms > 8.6 ps-1 @ 95% confidence Sensitivity: 13.0 ps-1 @ 95% confidence Limit: ms > 14.8 ps-1 @ 95% confidence Expected Limit: 14.1 ps-1 @ 95% confidence • Excellent performance of the Tevatron. • Development of Same Side Kaon Tagger which will ease the total tagging power by about 2.5 (CDF) • D0 has excellent opposite side tagger performance. • CDF preliminary: • D0 Final (hep-ex/0603029, submitted to PRL): • We are on the edge of Bs mixing measurement and entering into the precision era. Amplitude Scan Likelihood scan 17 < Dms < 21 ps-1 @ 90% CL Most probable value of Dms = 19 ps-1 Md. Naimuddin

  29. FUTURE IMPROVEMENTS Several major improvements are expected in the future: • CDF: • Improved selection in hadronic modes using Neural Networks • Use semileptonic events from other triggers. • Improve vertex resolution. • Use same side Kaon tagger. • D0: • More decay modes (DsK*K, 3, Ks, Bse Ds X ) • Use of same side tagging. • Use of hadronic modes. • Additional Layer of silicon. • Proposal to increase the bandwidth. More data: On track for 4-8 fb-1 of data by 2009. Md. Naimuddin

  30. Back-up slides Md. Naimuddin

  31. Backup-1 Time evolution follows from a simple perturbative solution to the schrondinger’s equation Eigenvalues are, In case  0, Measure of the amount by which |BL> and |BH> differ from CP eigenstates Md. Naimuddin

  32. Backup-2 1 ( ) ( ) - G = G ± D e t P t 1 cos mt u , m In the limit of no CP violation in mixing (q/p =1), unmixed and mixed decay probabilities become These oscillations can be used to measure the fundamental parameters of the standard Model and have other far reaching effects such as breaking the matter anti-matter symmetry of the Universe. Constraining the CKM matrix redundantly using different measurements of the angles/sides is a sensitive probe of New Physics Md. Naimuddin

  33. Backup-3 Md. Naimuddin

  34. Backup-4 Md. Naimuddin

  35. Backup-5 Md. Naimuddin

  36. Backup-6 Md. Naimuddin

  37. Backup-7 WA+CDF+D0 Md. Naimuddin

  38. Backup-8 Comparison with other experiments at ms=15 ps-1 Md. Naimuddin

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