# Presentation: 415390

## Sergey Burdin
FNAL
DØ Collaboration
8/12/2005
Chicago Flavor

***FNAL***
***DØ Collaboration***
**8/12/2005**
**Chicago Flavor**

- New Bs Mixing Result from DØ

## Bs mixing with Bs Ds μX, Ds π, K*K  and   opposite-side flavor tagging

** ∫*****L*****d*****t*****=610pb****-1 ****(*****All available statistics up to June 2005*****)**
** ****Many people contributed to this work**

- Bs mixing with Bs Ds **μ****X,** Ds ******π****, K*********K**  and   opposite-side flavor tagging

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## History: from Simple to Complex

** ****2003**
** ****Reconstruction of semileptonic B decays:                              ****μ****D****0****, ****μ****D*****±****, ****μ****D****±****, ****μ****D****s**
** ****Understanding of sample composition, resolution,                  K-factor (momentum of non-reconstructed particles)**
** ****Precise measurement: ****B****+****/B****0**** lifetime ratio ****(**_[PRL 94, 182001 (2005)](http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PRLTAO000094000018182001000001&idtype=cvips)_**)**
-  **2004**
-  **Bd mixing measurements**
** ****Opposite-side muon tagging **
** ****Same-side tagging**
-  **2005**
** ****Bs mixing measurements**
**First result for Moriond 2005**
**Update for EPS 2005 **
**Considerable improvement**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## B Mixing Analyses

** ****Signal Selection**
** ****Initial and final state flavor tagging**
** ****Study of time evolution of tagged B signal**
** ****Use Visible Proper Decay Length for semileptonic decays**
** ****Use special variable “Asymmetry”**
** ****Fit **
**Comparison with expected asymmetry gives ****Δ****m**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Bs data sample @ DØ

** ****World largest                                     sample**
** ****Data up to end of May 2005 (~610pb****-1****)**

**15640****±190 Ds************π**** **

**4349****±152 D****±************π**** **

**18780±782**

**3233±208**

**14112±910**

**Charge of muon gives **
**the final state tagging**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Signal Selection

** ****A set of discriminating variables is constructed for a given event**
** ****Cut on combined variable**
** *****f******s******(x******i******)***** and *****f******b******(x******i******)***** --- pdf for signal and background**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Improvement wrt Moriond

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Analyses road map

** ****Binned asymmetry**
** ****Asymmetry fitting procedure **
** ****Essentially the same as for the lifetime ratio and Bd mixing analyses**
**Inputs to the fitting procedure**
** ****MC **
** ****sample composition**
** ****K-factor taking into account non-reconstructed particles**
** ****Efficiencies**
** ****Visible Proper Decay Length (VPDL) resolution**
** ****Scale factor for VPDL resolution from tuning procedure**
** ****Tagging algorithm tested and its dilution determined from Bd and Bu semileptonic samples **

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Initial State Tagging

**Initially bb pair is produced – use decays of b to tag flavor of b **
**Flavor at production moment determined by sign of ****opposite side muon (electron), tracks from Secondary Vertex and Jet Charge**
** ****For example**
******+ ********-  ******** no oscillation**
******+ ********+ ****or ********- ********-  ******** oscillation**
**Beware: Additional dilution from oscillations on the opposite side**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Initial state flavour tagging

**For this analysis, we use opposite-side flavour tagging to determine the flavour of a given **
**B meson at production****. b quarks are produced in pairs (b-b); we use the decay products of the “other b” to infer the initial flavour of the B.**
**A method based on ****likelihood ratios**** is used to ****combine different discriminating variables**** into one continuous tagging variable *****d***** (b-like: *****d*****>0 ; b-like: *****d*****<0). ****We distinguish different categories of events, and use the following ****discriminating variables****:**
**  ****If an ****opposite muon**** [cos ********(p********,p****B****) < 0.8] is found:**
**     ****Muon jet charge****:     constructed from p****T**** and charge **
**                 ****of muon and tracks within ********R < 0.5 of muon.**
**     ****Muon p****T****rel****:              transverse momentum of muon **
**                                    ****w.r.t. nearest track-jet.**
**     ****If ****secondary vertex**** is found (e.g. from B decay): **
**        ****Secondary vertex jet charge constructed **
**        ****from charge and momenta of tracks from vertex.**
**  ****If an ****opposite electron**** [cos ********(p****e****, p****B****) < 0.5] is found:**
**      ****Charge of the electron**
**  ****Otherwise:**
**        ****Secondary vertex jet charge**
**        ****p****T**** of secondary vertex**
**        ****Event jet charge****:   constructed from charge and **
**                         ****momenta of all tracks at ********R > 1.5 from B.**

**Distribution of combined variable**
**in data samples enriched in B****0**** and in B****0****:**

**B****0****-enriched**

**B****0****-enriched**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Dilution from Δmd measurement

**B****d**** oscillation measurement                                           with the same opposite-side                                        tagger as for B****s**
******m****d****= 0.501********0.030±0.016ps****-1**** **
** ****Dilutions**
** ****D****(B****d****)=0.414********0.023±0.017  **
** ****D****(B****u****)=0.368********0.016±0.008 ******** Used for systematic error**
** ****MC shows that dilutions for B****s**** and B****d**** are in agreement**
** ****Dilution for B****d**** agrees in data and MC **
-  Better use of tag variables  **ε****D****2****=2.17±0.13±0.09 %**** **

**Combined dilution:  D=0.384±0.013±0.008**
**ε****D****2****=1.94±0.14±0.09 %      **

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Tagged Bs→DsμX events

** ****Tagging efficiency --- 12.3%**
** ****In agreement with B****d**** and B****u**

**1917****± 66 Ds************π**** candidates**

**566****±55 D****±************π**** candidates**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Measurement of Bs Oscillation Frequency

***Amplitude fit ******= ******Fourier analysis + Maximum likelihood fit*****              can be used for the ****Δ****m****s ****measurements**

**If *****A=1, *****the ****Δ****m’****s ****is a measurement of Bs oscillation frequency,**
** ****otherwise *****A*****=0**

**Need to know dilution (from ****Δ****m****d**** analysis)**

**Amplitude fit for Bd mixing**
** ****Is not the best method to determine the oscillation frequency**
** ****Good to establish the oscillation frequency range**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Asymmetry in μDs sample (π mode)

**Expected curve is affected by bin width, resolution and K-factor **

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Asymmetry for K*K decay mode

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Asymmetries in μDs and μD± samples (large bin)

** ****See oscillations in ****μ****D****±**** (D****±************π****) sample**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Asymmetry Fitting Procedure

**Use amplitude method to set a limit on the B****s**** oscillation frequency**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Asymmetry Fitting Procedure

** ****For given decay mode *****j*****:**
** ****For given VPDL interval *****i*****:**
** ****Minimize *****χ******2*****  for given ****Δ****m****s**** in range                  from 1 to 20 ps****-1**** with step 1 ps****-1**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Sample Composition

**Inputs from MC**
** ****Sample composition                                                                                    for signal peak**
**+ 3.5±2.5% contribution of                from gluon splitting **

| Decay | Sample composition |
| --- | --- |
| Bs→Dsμν | 21.7% |
| Bs→D*sμν | 60.7% |
| Bs→D*0sμν | 1.4% |
| Bs→D*1sμν | 3.1% |
| Bs→Dsτν | 1.3% |
| Bs→DsDsX | 2.9% |
| Bs→DsDX | 0.9% |
| B0→DsDX | 4.0% |
| B-→DsDX | 4.1% |

**Useful signal ****— ****88.3%**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

##            contamination

** ****From MC: **
** ****tagging suppresses the ccbar by factor of ~3**
** ****From lifetime ratio analysis: **
** ****10±7% contamination**
** ****Result: **
** ****3.5±2.5% contribution**
**VPDL distribution from MC**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## K-factors

| Decay | <k> |
| --- | --- |
| Bs→Dsμν | 0.881 |
| Bs→D*sμν | 0.861 |
| Bs→D*0sμν | 0.815 |
| Bs→D*1sμν | 0.830 |
| Bs→DsDsX | 0.762 |
| B0→DsDX | 0.681 |
| B-→DsDX | 0.687 |

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Efficiency vs VPDL

**Use MC **
**Have lifetime cuts in the analysis   ****→ efficiency (VPDL)**
**In the Bs oscillation analysis the asymmetry in the range                      [-0.01, 0.06] cm is the most important                                           ****→ efficiency shape is a large effect over all sensitivity region**
** ****Would cancel out if not the sample composition**
** ****Good news : same turn-on shape for different processes**

**Signal**

**Background**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## VPDL Resolution

** ****Understanding of resolution is crucial for ****Δ****m****s**** measurement**
** ****Measured and**** ****tuned tracking errors in data and MC**
** ****Tracking errors depend on**
**Track momentum and angles**
**Silicon detector hit configuration and cluster width**
** ****~150 configurations are being considered**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Tuning VPDL resolution

**Data after tuning**

**MC after tuning**

**ln(****σ****2****IP****)**

**-ln(****p****2****sin****3****θ****)**

**Track IP errors**

**IP resolution**

**ln(****σ****2****IP****)**

**ln(****σ****2****IP****)**

**ln(****σ****2****IP****)**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## VPDL Resolution

**Resolution described by 3 gaussians **
**One scale factor for all 3 gaussians: 1.142±0.020**
** ****Tuning is crucial for event by event fit**

- Dependence of resolution
- from VPDL

**MC**

**MC**

**Before **
**tuning**

**After **
**tuning**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Result on Bs oscillations in π mode

** ****1.7 times better than our Moriond result**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Result on Bs oscillations in K*K mode

** ****New Result**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Systematic Errors

**Tagging Purity**

**Resolution**

**Br(B****s********D****s****μ****X****)**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Combined DØ result in π and K*K modes

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Sensitivity in Comparison

**(this analysis, 610 pb****-1****)**

**(prior to this conference, 355 pb****-1****)**

***Jan Stark, EPS 2005***

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Bs Mixing Projections

**Planned hardware improvement**
**L3 bandwidth increase from 50 to 100 Hz**
** ****Expect considerable increase in signal yield**
** ****Tests are successful !**
**Layer0**
**Improvement in decay length resolution**

**Analysis improvement**
** ****event by event fit**
** ****better tagging**
** ****Improved OST**
** ****Same-Side Tagging**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## New Tevatron Combination

** ****Combined Tevatron average comparable to the best single measurement**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## New World Combination

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Experimental Status of Unitarity Triangle

**Present and future experiments to improve our knowledge of the Unitarity Triangle **
**B-factories**
-  Access to Bd mesons
-  **Δ*****m******d***** = (0.510 ± 0.005) ps****–1****    **
**Tevatron and LHC**
- Access to all B hadrons (Bd, Bs, Bc, b etc)
- Measurement of   ms/md
- Strong constraint on one of the triangle's sides

**HFAG – Winter 2005**

- S.Burdin /FNAL/ @ CF

- 8/12/2005

## Conclusion

** ****We are entering era when Bs mixing will be defined by the Tevatron results**
** ****Our result has the second best sensitivity (after ALEPH inclusive lepton analysis)**
** ****Impressive team work of many people**
** ****Good prospects**
** ****10-fold increase statistics during next 3 years (more lumi + increased bandwidth)**
** ****Layer 0**** **
** ****Now it is clear that we will push the sensitivity well beyond 20 ps****-1**** **
** ****measure ****Δ****m****s ****if it is close to 20 ps****-1**

- S.Burdin /FNAL/ @ CF

- 8/12/2005