# Presentation: 265572

## Some New Results in Heavy Flavor Physics

**G.Borissov, Lancaster University, UK**
**representing DØ Collaboration**

## Many new results in heavy flavors physics:

**Properties of top quark**
**B****s**** lifetime from B****s********J/****ψ φ;**
**Br(B****s**** ******** ****μ****+****μ****-****);**
**B****d**** oscillations;**
**Signals in B****s ******** ****μ νD****s****;**
**Λ****b**** lifetime;**
**B****** ****masses;**
**Properties of X(3872); **
**B****c**** lifetime;**

**in this talk**

**Thanks to excellent performance of Tevatron accelerator and DØ detector**

**talk of A.Nomerotski**

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

- 4 October, 2004

## Tevatron Performance

**Peak luminosity above 1·10****32**** cm****-2****sec****-1**** achieved;**
**Reliable operation of accelerator: in stores ~120 hours/week;**
**Expected peak luminosity 3·10****32**** cm****-2****sec****-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 October, 2004

## Slide 4

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

- 4 October, 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

- 4 October, 2004

## Top quark Studies

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

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

- 4 October, 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

- 4 October, 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

- 4 October, 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

- 4 October, 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

- 4 October, 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

- 4 October, 2004

## Bs Studies

**Properties of B****s ****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;
**B****s**** is abundantly produced at Tevatron and can be reconstructed in both semileptonic and exclusive decays;**

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

- 4 October, 2004

## Bs lifetime measurement

**In this measurement the decay B****s******** J/****ψ φ is used;**
**In parallel, the lifetime of B****d**** in ****B****d******** J/****ψ K********* is measured – very similar topology;**
**Simultaneous measurement of B****d**** and B****s**** lifetimes  reduces systematics in τ(B****s****) / τ(B****d****) ratio;**
**Important step towards measurement of lifetime difference of CP-even and CP-odd B****s**** states.**

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

- 4 October, 2004

## Signal selection

**cτ/σ(cτ) > 5**

**cτ/σ(cτ) > 5**

**~220 pb****-1**** of DØ Run II data used**

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

- 4 October, 2004

## Lifetime fit

**Two dimensional unbinned likelihood fit is used**

**Systematic uncertainties**

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

- 4 October, 2004

## Bs Lifetime Results

**This result agrees with other measurements of τ(B****s****)**

| Experiment | τ(Bs) |
| --- | --- |
| DØ, this measurement | 1.444+0.098-0.090±0.020 |
| CDF (Run II) prelim  | 1.369 ±0.100+0.008-0.010 |
| CDF(Run I) semileptonic | 1.36 ±0.090+0.06-0.05 |
| ALEPH | 1.47 ±0.14 ±0.08 |
| DELPHI | 1.42+0.14-0.13 ±0.03 |
| OPAL | 1.50+0.16-0.15 ±0.04 |

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

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

- 4 October, 2004

## Search for Bsμ+μ-

|  | Br(Bdl+l-) | Br(Bsl+l-) |
| --- | --- | --- |
| l = e | (3.4±2.3) ·10-15 | (8.0±3.5) ·10-14 |
| l=μ | (1.5±0.9) ·10-10 | (3.4±0.5) ·10-9 |
| l=τ | (3.1±1.9) ·10-8 | (7.4±1.9) ·10-7 |

**Standard Model prediction**

|  | Br(Bdl+l-) | Br(Bsl+l-) |
| --- | --- | --- |
| l = e | < 5.9 ·10-6 | < 5.4 ·10-5 |
| l=μ | < 1.5 ·10-7 | <5.8 ·10-7 |
| l=τ | < 2.5% | < 5.0% |

**Current 90%CL limits**

**Rare B decays to leptons have very small expected branching rates in SM.**
**They can be significantly higher in different  SM extensions.**

**Example: SO(10) symmetry breaking model**

**Contours of constant Br(B****s********μ****+****μ****-****)**

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

- 4 October, 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

- 4 October, 2004

## Event Preselection

**About 38000 candidates remain after preselection**

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

- 4 October, 2004

## Discriminating Variables

**Pointing angle: angle between B****s**** momentum and direction from primary to secondary vertex;**
**Transverse decay length significance: L****T****/σ(L****T****) ; **
**Isolation:**

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

- 4 October, 2004

## Optimization Procedure

**~80 pb****-1**** of data is used to optimize the selection;**
**Signal band is defined as m(B****s****DØ****) ± 180 MeV (90 MeV is B****s********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 B****s********μ****+****μ****-****;**

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

- 4 October, 2004

## Surviving Events

| cut | Signal MC | exp. background | Signal |
| --- | --- | --- | --- |
| Pointing angle | 8016 | 573±14 | 580 |
| Decay length significance | 3847 | 4.3±1.2 | 5 |
| Isolation | 3746 | 3.7±1.1 | 4 |

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

- 4 October, 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

- 4 October, 2004

## Systematic uncertainties

**Br(B****s********μ****+****μ****-****) Result**

|  | This measurement | Existing limit (CDF) |
| --- | --- | --- |
| 90% CL | < 3.8·10-7 | < 5.8·10-7 |
| 95% CL | < 4.6·10-7 | < 7.5·10-7 |

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

- 4 October, 2004

## Preparing for Bs oscillations

**B****s**** oscillation measurement – very interesting and very difficult task;**
**Requires both selection of B****s**** signal and tagging its initial state (b or bbar);**
**Currently DØ selects B****s**** in semileptonic decays;**
**We also develop methods of B****s**** selection in hadronic decays; **

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

- 4 October, 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 B****d**** oscillation;**

**Same side tagging result**

| Tagging | ε | D | εD2 |
| --- | --- | --- | --- |
| opposite muon | 0.05 | 0.46 | 0.010 |
| Same side | 0.75 | 0.12 | 0.010 |
| Same side + Jet charge | 0.68 | 0.15 | 0.015 |

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

- 4 October, 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

- 4 October, 2004