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Some New Results in Heavy Flavor Physics

Some New Results in Heavy Flavor Physics. G.Borissov, Lancaster University, UK representing DØ Collaboration. Many new results in heavy flavors physics:. in this talk. Properties of top quark B s lifetime from B s J/ ψ φ; Br(B s  μ + μ - ); B d oscillations;

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Some New Results in Heavy Flavor Physics

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  1. Some New Results in Heavy Flavor Physics G.Borissov, Lancaster University, UK representing DØ Collaboration

  2. Many new results in heavy flavors physics: in this talk • Properties of top quark • Bs lifetime from BsJ/ψ φ; • Br(Bs μ+μ-); • Bd oscillations; • Signals in Bs  μ νDs; • Λb lifetime; • B** masses; • Properties of X(3872); • Bc lifetime; talk of A.Nomerotski Thanks to excellent performance of Tevatron accelerator and DØ detector G.Borissov, Dzero Hot Topics, FPCP-2004

  3. Tevatron Performance • Peak luminosity above 1·1032 cm-2sec-1 achieved; • Reliable operation of accelerator: in stores ~120 hours/week; • Expected peak luminosity 3·1032 cm-2sec-1 by 2007; • delivered luminosity to each experiment ~4-8 fb-1 by the end of 2009; G.Borissov, Dzero Hot Topics, FPCP-2004

  4. G.Borissov, Dzero Hot Topics, FPCP-2004

  5. Integrated Luminosity • Almost 0.5 fb-1 recorded in DØ; • Most of analyses use only 30-50% of this statistics more events available  big room for improvement. G.Borissov, Dzero Hot Topics, FPCP-2004

  6. Top quark Studies Provide important constraints on the SM Higgs mass and new physics contribution G.Borissov, Dzero Hot Topics, FPCP-2004

  7. Top Quark Mass Measurement • New statistics from Run II (~160 pb-1); • 191 events with lepton + 4 jets selected; • 4 topological variables used to separate ttbar and W+jets background. They are combined into a single discriminant. G.Borissov, Dzero Hot Topics, FPCP-2004

  8. Measurement Methods • 4 Jets and W can be combined into 2 top quarks in 12 possible ways; • Two alternative measurement methods used; • Template method: • apply cut on discriminant; • select best mass hypothesis among all jet permutations; • Ideogram method: • discriminant is used to compute the purity of ttbar candidate on event by event basis; • use all jet permutations with weight depending on the χ2 of each combination hypothesis. G.Borissov, Dzero Hot Topics, FPCP-2004

  9. Top Quark Mass Results • Consistent preliminary results are obtained (160 pb-1): • Leading systematic uncertainty is from ttbar modeling, can be improved in the futre; • In addition, new result published (Nature (429), 638 (2004)) using Run I data (single most precise mass measurement): G.Borissov, Dzero Hot Topics, FPCP-2004

  10. Br(tWb)/Br(t Wq) • This ratio should be close to 1 in the SM, assuming unitarity of CKM matrix; • Should be verified experimentally; • Measurement is performed using a double tagging technique with b-tagging applied to the t-tbar sample (lepton plus jets). G.Borissov, Dzero Hot Topics, FPCP-2004

  11. R=Br(tWb)/Br(t Wq) Result • Two b-tagging methods are used: • Counting signed impact parameter; • Secondary vertex Tagger; • Consistent preliminary results are obtained: • This result is consistent with R=1. G.Borissov, Dzero Hot Topics, FPCP-2004

  12. Bs Studies • Properties of Bs are not well known yet; • This particle is not accessible at Υ(4s); • Have many interesting features: • Bs oscillation; • Lifetime difference of CP-even and CP-odd state; • CP violation – very small in SM, thus can be sensitive to the new physics; • Rare decays may be enhanced; • Bs is abundantly produced at Tevatron and can be reconstructed in both semileptonic and exclusive decays; G.Borissov, Dzero Hot Topics, FPCP-2004

  13. Bs lifetime measurement • In this measurement the decay Bs J/ψ φ is used; • In parallel, the lifetime of Bd in Bd J/ψ K* is measured – very similar topology; • Simultaneous measurement of Bd and Bs lifetimes reduces systematics in τ(Bs) / τ(Bd) ratio; • Important step towards measurement of lifetime difference of CP-even and CP-odd Bs states. G.Borissov, Dzero Hot Topics, FPCP-2004

  14. Signal selection ~220 pb-1 of DØ Run II data used cτ/σ(cτ) > 5 cτ/σ(cτ) > 5 G.Borissov, Dzero Hot Topics, FPCP-2004

  15. Lifetime fit Two dimensional unbinned likelihood fit is used Systematic uncertainties G.Borissov, Dzero Hot Topics, FPCP-2004

  16. Bs Lifetime Results (FNAL-PUB-04/225-E, submitted to PRL) This result agrees with other measurements of τ(Bs) G.Borissov, Dzero Hot Topics, FPCP-2004

  17. Search for Bsμ+μ- Rare B decays to leptons have very small expected branching rates in SM. They can be significantly higher in different SM extensions. Standard Model prediction Current 90%CL limits Example: SO(10) symmetry breaking model Contours of constant Br(Bsμ+μ-) G.Borissov, Dzero Hot Topics, FPCP-2004

  18. Data sample • DØ has very efficient di-muon triggers; • Use data collected in 2002 - April 2004; • Sample corresponds to ~250 pb-1 integrated luminosity. G.Borissov, Dzero Hot Topics, FPCP-2004

  19. Event Preselection About 38000 candidates remain after preselection G.Borissov, Dzero Hot Topics, FPCP-2004

  20. Discriminating Variables • Pointing angle: angle between Bs momentum and direction from primary to secondary vertex; • Transverse decay length significance: LT/σ(LT) ; • Isolation: G.Borissov, Dzero Hot Topics, FPCP-2004

  21. Optimization Procedure • ~80 pb-1 of data is used to optimize the selection; • Signal band is defined as m(BsDØ) ± 180 MeV (90 MeV is Bsμ+μ- resolution in MC); • Signal distributions are taken from MC and background from side bands; • Perform random grid search of 3 discriminating variables and maximize the sensitivity to the signal. • Signal region in data is kept as a black box, open it only after finalizing and fixing the selection procedure; • Number of events in side bands is used to estimate the background for Bsμ+μ-; G.Borissov, Dzero Hot Topics, FPCP-2004

  22. Surviving Events G.Borissov, Dzero Hot Topics, FPCP-2004

  23. Normalization Channel • B+J/ψ K+ (J/ψ μ+μ-) is used for normalization; • muon selection efficiency cancels in the ratio; • Systematics from discriminating variables significantly reduced. G.Borissov, Dzero Hot Topics, FPCP-2004

  24. Systematic uncertainties Br(Bsμ+μ-) Result G.Borissov, Dzero Hot Topics, FPCP-2004

  25. Preparing for Bs oscillations • Bs oscillation measurement – very interesting and very difficult task; • Requires both selection of Bs signal and tagging its initial state (b or bbar); • Currently DØ selects Bs in semileptonic decays; • We also develop methods of Bs selection in hadronic decays; G.Borissov, Dzero Hot Topics, FPCP-2004

  26. Initial State Tagging • Three different methods are developed: • Opposite muon tagging; • Opposite jet charge tagging; • Same side tagging; • Their performance is verified in data using Bd oscillation; Same side tagging result G.Borissov, Dzero Hot Topics, FPCP-2004

  27. Conclusions • Many new results in heavy flavor physics are obtained by DØ collaboration; • All of them are competitive or the world’s best measurements; • DØ will continue research in this direction with the main emphasis on studies complementary to B-factories – those, involving B hadron states not produced at the Υ(4s). G.Borissov, Dzero Hot Topics, FPCP-2004

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