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Some New Results in Heavy Flavor Physics

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Some New Results in Heavy Flavor Physics

G.Borissov, Lancaster University, UK

representing DÃ˜ Collaboration

in this talk

- Properties of top quark
- Bs lifetime from Bsï‚®J/Ïˆ Ï†;
- Br(Bsï‚® Î¼+Î¼-);
- Bd oscillations;
- Signals in Bs ï‚® Î¼ Î½Ds;
- Î›b lifetime;
- B** masses;
- Properties of X(3872);
- Bc lifetime;

talk of A.Nomerotski

Thanks to excellent performance of Tevatron accelerator and DÃ˜ detector

G.Borissov, Dzero Hot Topics, FPCP-2004

- Peak luminosity above 1Î‡1032 cm-2sec-1 achieved;
- Reliable operation of accelerator: in stores ~120 hours/week;
- Expected peak luminosity 3Î‡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

- Almost 0.5 fb-1 recorded in DÃ˜;
- Most of analyses use only 30-50% of this statistics
more events available ï‚® big room for improvement.

G.Borissov, Dzero Hot Topics, FPCP-2004

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

G.Borissov, Dzero Hot Topics, FPCP-2004

- 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

- 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 Ï‡2 of each combination hypothesis.

G.Borissov, Dzero Hot Topics, FPCP-2004

- 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

- 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

- 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

- Properties of Bs are not well known yet;
- This particle is not accessible at Î¥(4s);
- Have many interesting features:
- Bs oscillation;
- Lifetime difference of CP-even and CP-odd state;
- CP violation â€“ 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

- In this measurement the decay Bsï‚® J/Ïˆ Ï† is used;
- In parallel, the lifetime of Bd in Bdï‚® J/Ïˆ K* is measured â€“ very similar topology;
- Simultaneous measurement of Bd and Bs lifetimes reduces systematics in Ï„(Bs) / Ï„(Bd) ratio;
- Important step towards measurement of lifetime difference of CP-even and CP-odd Bs states.

G.Borissov, Dzero Hot Topics, FPCP-2004

~220 pb-1 of DÃ˜ Run II data used

cÏ„/Ïƒ(cÏ„) > 5

cÏ„/Ïƒ(cÏ„) > 5

G.Borissov, Dzero Hot Topics, FPCP-2004

Two dimensional unbinned likelihood fit is used

Systematic uncertainties

G.Borissov, Dzero Hot Topics, FPCP-2004

(FNAL-PUB-04/225-E, submitted to PRL)

This result agrees with other measurements of Ï„(Bs)

G.Borissov, Dzero Hot Topics, FPCP-2004

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(Bsï‚®Î¼+Î¼-)

G.Borissov, Dzero Hot Topics, FPCP-2004

- DÃ˜ 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

About 38000 candidates remain after preselection

G.Borissov, Dzero Hot Topics, FPCP-2004

- Pointing angle: angle between Bs momentum and direction from primary to secondary vertex;
- Transverse decay length significance: LT/Ïƒ(LT) ;
- Isolation:

G.Borissov, Dzero Hot Topics, FPCP-2004

- ~80 pb-1 of data is used to optimize the selection;
- Signal band is defined as m(BsDÃ˜) Â± 180 MeV (90 MeV is Bsï‚®Î¼+Î¼- 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 Bsï‚®Î¼+Î¼-;

G.Borissov, Dzero Hot Topics, FPCP-2004

G.Borissov, Dzero Hot Topics, FPCP-2004

- B+ï‚®J/Ïˆ K+ (J/Ïˆ ï‚®Î¼+Î¼-) is used for normalization;
- muon selection efficiency cancels in the ratio;
- Systematics from discriminating variables significantly reduced.

G.Borissov, Dzero Hot Topics, FPCP-2004

Br(Bsï‚®Î¼+Î¼-) Result

G.Borissov, Dzero Hot Topics, FPCP-2004

- Bs oscillation measurement â€“ very interesting and very difficult task;
- Requires both selection of Bs signal and tagging its initial state (b or bbar);
- Currently DÃ˜ selects Bs in semileptonic decays;
- We also develop methods of Bs selection in hadronic decays;

G.Borissov, Dzero Hot Topics, FPCP-2004

- 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

- Many new results in heavy flavor physics are obtained by DÃ˜ collaboration;
- All of them are competitive or the worldâ€™s best measurements;
- DÃ˜ will continue research in this direction with the main emphasis on studies complementary to B-factories â€“ those, involving B hadron states not produced at the Î¥(4s).

G.Borissov, Dzero Hot Topics, FPCP-2004