Some new results in heavy flavor physics
Sponsored Links
This presentation is the property of its rightful owner.
1 / 27

Some New Results in Heavy Flavor Physics PowerPoint PPT Presentation


  • 63 Views
  • Uploaded on
  • Presentation posted in: General

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;

Download Presentation

Some New Results in Heavy Flavor Physics

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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

  • 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

  • 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


G.Borissov, Dzero Hot Topics, FPCP-2004


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

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

G.Borissov, Dzero Hot Topics, FPCP-2004


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

  • 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

  • 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)

  • 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

  • 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


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


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

~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

Two dimensional unbinned likelihood fit is used

Systematic uncertainties

G.Borissov, Dzero Hot Topics, FPCP-2004


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 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

  • 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

About 38000 candidates remain after preselection

G.Borissov, Dzero Hot Topics, FPCP-2004


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

  • ~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

G.Borissov, Dzero Hot Topics, FPCP-2004


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

Br(Bsμ+μ-) Result

G.Borissov, Dzero Hot Topics, FPCP-2004


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

  • 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

  • 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


  • Login