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New Bs Mixing Result from DØ

New Bs Mixing Result from DØ . Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor. Bs mixing with B s  D s μ X, D s   π , K * K and opposite-side flavor tagging. DØ conference notes 4878 & 4881 ∫ L d t =610pb -1 ( All available statistics up to June 2005 )

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New Bs Mixing Result from DØ

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  1. New Bs Mixing Result from DØ Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor

  2. Bs mixing with Bs DsμX,Ds π, K*Kand opposite-side flavor tagging • DØ conference notes 4878 & 4881 • ∫Ldt=610pb-1 (All available statistics up to June 2005) • Many people contributed to this work S.Burdin /FNAL/ @ CF

  3. History: from Simple to Complex • 2003 • Reconstruction of semileptonic B decays: μD0, μD*±, μD±, μDs • Understanding of sample composition, resolution, K-factor (momentum of non-reconstructed particles) • Precise measurement: B+/B0 lifetime ratio (PRL 94, 182001 (2005)) • 2004 • Bd mixing measurements • Opposite-side muon tagging • Same-side tagging • 2005 • Bs mixing measurements • First result for Moriond 2005 • Update for EPS 2005 • Considerable improvement S.Burdin /FNAL/ @ CF

  4. B Mixing Analyses • Signal Selection • Initial and final state flavor tagging • Study of time evolution of tagged B signal • Use Visible Proper Decay Length for semileptonic decays • Use special variable “Asymmetry” • Fit • Comparison with expected asymmetry gives Δm S.Burdin /FNAL/ @ CF

  5. Bs data sample @ DØ Charge of muon gives the final state tagging • World largest sample • Data up to end of May 2005 (~610pb-1) 18780±782 3233±208 14112±910 4349±152 D±π 15640±190 Dsπ S.Burdin /FNAL/ @ CF

  6. Signal Selection • A set of discriminating variables is constructed for a given event • Cut on combined variable • fs(xi) and fb(xi) --- pdf for signal and background S.Burdin /FNAL/ @ CF

  7. Improvement wrt Moriond S.Burdin /FNAL/ @ CF

  8. Analyses road map • Binned asymmetry • Asymmetry fitting procedure • Essentially the same as for the lifetime ratio and Bd mixing analyses • Inputs to the fitting procedure • MC • sample composition • K-factor taking into account non-reconstructed particles • Efficiencies • Visible Proper Decay Length (VPDL) resolution • Scale factor for VPDL resolution from tuning procedure • Tagging algorithm tested and its dilution determined from Bd and Bu semileptonic samples S.Burdin /FNAL/ @ CF

  9. Initial State Tagging • Initially bb pair is produced – use decays of b to tag flavor of b • Flavor at production moment determined by sign of opposite side muon (electron), tracks from Secondary Vertex and Jet Charge • For example • m+ m-  no oscillation • m+ m+ or m- m-  oscillation • Beware: Additional dilution from oscillations on the opposite side S.Burdin /FNAL/ @ CF

  10. Initial state flavour tagging For this analysis, we use opposite-side flavour tagging to determine the flavour of a given B meson at production. b quarks are produced in pairs (b-b); we use the decay products of the “other b” to infer the initial flavour of the B. A method based on likelihood ratios is used to combine different discriminating variables into one continuous tagging variable d (b-like: d>0 ; b-like: d<0). We distinguish different categories of events, and use the following discriminating variables: If an opposite muon [cos (p,pB) < 0.8] is found: Muon jet charge: constructed from pT and charge of muon and tracks within R < 0.5 of muon. Muon pTrel: transverse momentum of muon w.r.t. nearest track-jet. If secondary vertex is found (e.g. from B decay): Secondary vertex jet charge constructed from charge and momenta of tracks from vertex. If an opposite electron [cos (pe, pB) < 0.5] is found: Charge of the electron Otherwise: Secondary vertex jet charge pT of secondary vertex Event jet charge: constructed from charge and momenta of all tracks at R > 1.5 from B. Distribution of combined variable in data samples enriched in B0 and in B0: B0-enriched B0-enriched S.Burdin /FNAL/ @ CF

  11. Dilution from Δmd measurement • Bd oscillation measurement with the same opposite-side tagger as for Bs • Dmd= 0.5010.030±0.016ps-1 • Dilutions • D(Bd)=0.4140.023±0.017 • D(Bu)=0.3680.016±0.008  Used for systematic error • MC shows that dilutions for Bs and Bd are in agreement • Dilution for Bd agrees in data and MC • Better use of tag variables  εD2=2.17±0.13±0.09 % Combined dilution: D=0.384±0.013±0.008 εD2=1.94±0.14±0.09 % S.Burdin /FNAL/ @ CF

  12. Tagged Bs→DsμX events 566±55 D±π candidates • Tagging efficiency --- 12.3% • In agreement with Bd and Bu 1917± 66 Dsπ candidates S.Burdin /FNAL/ @ CF

  13. Measurement of Bs Oscillation Frequency Amplitude fit = Fourier analysis + Maximum likelihood fit can be used for the Δms measurements Need to know dilution (from Δmd analysis) If A=1, the Δm’s is a measurement of Bs oscillation frequency, otherwise A=0 • Amplitude fit for Bd mixing • Is not the best method to determine the oscillation frequency • Good to establish the oscillation frequency range S.Burdin /FNAL/ @ CF

  14. Asymmetry in μDs sample (πmode) • Expected curve is affected by bin width, resolution and K-factor S.Burdin /FNAL/ @ CF

  15. Asymmetry for K*K decay mode S.Burdin /FNAL/ @ CF

  16. Asymmetries in μDs and μD± samples (large bin) • See oscillations in μD± (D±π) sample S.Burdin /FNAL/ @ CF

  17. Asymmetry Fitting Procedure Use amplitude method to set a limit on the Bs oscillation frequency S.Burdin /FNAL/ @ CF

  18. Asymmetry Fitting Procedure • For given decay mode j: • For given VPDL interval i: • Minimize χ2 for given Δms in range from 1 to 20 ps-1 with step 1 ps-1 S.Burdin /FNAL/ @ CF

  19. Sample Composition • Inputs from MC • Sample composition for signal peak • + 3.5±2.5% contribution of from gluon splitting Useful signal — 88.3% S.Burdin /FNAL/ @ CF

  20. contamination • From MC: • tagging suppresses the ccbar by factor of ~3 • From lifetime ratio analysis: • 10±7% contamination • Result: • 3.5±2.5% contribution • VPDL distribution from MC S.Burdin /FNAL/ @ CF

  21. K-factors S.Burdin /FNAL/ @ CF

  22. Efficiency vs VPDL • Use MC • Have lifetime cuts in the analysis → efficiency (VPDL) • In the Bs oscillation analysis the asymmetry in the range [-0.01, 0.06] cm is the most important → efficiency shape is a large effect over all sensitivity region • Would cancel out if not the sample composition • Good news : same turn-on shape for different processes Signal Background S.Burdin /FNAL/ @ CF

  23. VPDL Resolution • Understanding of resolution is crucial for Δms measurement • Measured andtuned tracking errors in data and MC • Tracking errors depend on • Track momentum and angles • Silicon detector hit configuration and cluster width • ~150 configurations are being considered S.Burdin /FNAL/ @ CF

  24. Tuning VPDL resolution Data before tuning MC before tuning ln(σ2IP) ln(σ2IP) IP resolution Track IP errors ln(σ2IP) Data after tuning MC after tuning ln(σ2IP) -ln(p2sin3θ) S.Burdin /FNAL/ @ CF

  25. VPDL Resolution Dependence of resolution from VPDL MC • Resolution described by 3 gaussians • One scale factor for all 3 gaussians: 1.142±0.020 • Tuning is crucial for event by event fit Before tuning After tuning MC S.Burdin /FNAL/ @ CF

  26. Result on Bs oscillations in πmode • 1.7 times better than our Moriond result S.Burdin /FNAL/ @ CF

  27. Result on Bs oscillations in K*Kmode • New Result S.Burdin /FNAL/ @ CF

  28. Systematic Errors Tagging Purity Br(BsDsμX) Resolution S.Burdin /FNAL/ @ CF

  29. Combined DØ result in πand K*K modes S.Burdin /FNAL/ @ CF

  30. Sensitivity in Comparison (prior to this conference, 355 pb-1) (this analysis, 610 pb-1) Jan Stark, EPS 2005 S.Burdin /FNAL/ @ CF

  31. Bs Mixing Projections We are here No upgrades Layer0 + L3 BW upgrades Analysis improvement • event by event fit • better tagging • Improved OST • Same-Side Tagging Planned hardware improvement • L3 bandwidth increase from 50 to 100 Hz • Expect considerable increase in signal yield • Tests are successful ! • Layer0 • Improvement in decay length resolution S.Burdin /FNAL/ @ CF

  32. New Tevatron Combination • Combined Tevatron average comparable to the best single measurement S.Burdin /FNAL/ @ CF

  33. New World Combination S.Burdin /FNAL/ @ CF

  34. Experimental Status of Unitarity Triangle • [ CKM constraint dominated by theory error ] • CKM fit predicts : Δmd = 0.47 ps–1 + 0.23 – 0.12 • CKM fit predicts : Δms = 18.3 ps–1 + 6.5 – 2.3 Δms measured Δms • Present and future experiments to improve our knowledge of the Unitarity Triangle • B-factories • Access to Bd mesons • Δmd = (0.510 ± 0.005) ps–1 • Tevatron and LHC • Access to all B hadrons (Bd, Bs, Bc, Lb etc) • Measurement of Dms/Dmd • Strong constraint on one of the triangle's sides HFAG – Winter 2005 S.Burdin /FNAL/ @ CF

  35. Conclusion • We are entering era when Bs mixing will be defined by the Tevatron results • Our result has the second best sensitivity (after ALEPH inclusive lepton analysis) • Impressive team work of many people • Good prospects • 10-fold increase statistics during next 3 years (more lumi + increased bandwidth) • Layer 0 • Now it is clear that we will push the sensitivity well beyond 20 ps-1 • measure Δms if it is close to 20 ps-1 S.Burdin /FNAL/ @ CF

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