Some new results in heavy flavor physics
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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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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

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


Tevatron performance

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


Some new results in heavy flavor physics

G.Borissov, Dzero Hot Topics, FPCP-2004


Integrated luminosity

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


Top quark studies

Top quark Studies

Provide important constraints on the SM Higgs mass and new physics contribution

G.Borissov, Dzero Hot Topics, FPCP-2004


Top quark mass measurement

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


Measurement methods

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


Top quark mass results

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


Br t wb br t wq

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


R br t wb br t wq result

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


B s studies

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


B s lifetime measurement

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


Signal selection

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


Lifetime fit

Lifetime fit

Two dimensional unbinned likelihood fit is used

Systematic uncertainties

G.Borissov, Dzero Hot Topics, FPCP-2004


B s lifetime results

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


Search for b s

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


Data sample

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


Event preselection

Event Preselection

About 38000 candidates remain after preselection

G.Borissov, Dzero Hot Topics, FPCP-2004


Discriminating variables

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


Optimization procedure

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


Surviving events

Surviving Events

G.Borissov, Dzero Hot Topics, FPCP-2004


Normalization channel

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


Systematic uncertainties

Systematic uncertainties

Br(Bsμ+μ-) Result

G.Borissov, Dzero Hot Topics, FPCP-2004


Preparing for b s oscillations

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


Initial state tagging

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


Conclusions

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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