# Presentation: 659620

## Bd  and Bs mixing at DØ 

***BEAUTY 2005, Assisi, Perugia***
- Tania Moulik,
- University of Kansas
- (For the DØ Collaboration)

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Outline

- Introduction
- Data taking, Triggers
- Bd mixing measurement
- Reconstruction
- Flavor Tagging
- Bs mixing measurement
- Decay modes
- Amplitude scan
- Sensitivity studies.

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Introduction

- Oscillations in the B-B system first observed by ARGUS in  (18 years since then!)
- Signalled a large top mass
- CP violation in B decays.
- Many measurements on Bd mixing – LEP, SLD, CDF, DØ, Belle, Babar
- Tevatron has unique opportunity to measure Bs mixing in 2 complementary analyses. ms (This talk) and s/s (Alberto Sanchez’s talk)

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

**Notes:**
ARGUS Bmixing result : H. Albrecht et. Al. (Phys. Lett. B 192, 245 (1987) )

## Bd and Bs Mixing

- Light and heavy B meson mass eigenstates differ from flavor eigenstates:

***B******d****** and Bs Mixing***

*W*

*W*

- b

- d(s)

- d(s)

*t*

- Time evolution follows the Schrodinger equation

- Vtb

- Vtb

- Vtd(s)

- Vtd

*t*

*t*

*t*

- b

- d(s)

- b

- d(s)

- Vtd(s)

- Vtd

*W*

- Vtb

- Vtb

*W*

- b

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Bd, Bs mixing

- The case with mixed and unmixed decay probabilities become,
- Extract mixing parameter m from asymmetry

***B******d******, B******s****** mixing***

- Time evolution of
- B and B states,

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

- Wolfenstein parametrisation - expansion in  ~ 0.22

- complex

- Ultimate Goal – Constraing the CKM matrix -
-    complex phase in the CKM matrix (CP violation).

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## md, ms, and CKM

- 

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

##  Data Taking

-  TeV

-  TeV

***Data taking ***
******

-  pb-1

-  pb-1

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

##  B physics triggers

- Single muon  Muon + track match at Level 1 and a muon at L2
-  Unbiased single muon triggers(PT>3,4,5) – Bd and Bs mixing, prescaled or turned off depending on luminosity.
- Impact parameter biased triggers – Hadronic decays (Not being used yet).

- Muon system  Layers of drift chambers and scintillators.
- Trigger (B mixing)   Single inclusive muon  trigger with |*********|*** < , PT > GeV,
- Dimuon trigger (second muon for tagging)

*Toroid*

- 

- 

- 

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Bd mixing – Motivation and Main ingredients

- High statistics sample
- - determines charge of the B on reconstruction side.
- Flavor tagging – determine charge of opposite B
- Sample composition – Other B decays contribute to the same final state.
- Validate flavor tagging to be used for main analysis, Bs mixing.

- -

- D , D*  D s

- W

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## D0 and B+ selection 

- D selection:
- 2 tracks, opposite charge,
- Pt>0.7, |<2.0
- Displaced vertex:
- d0/(d0) of tracks > 2
- Lxy/(lxy) > 4,
-  cos()> 0.9
- Good vertex fit.
- D (B+) selection:
- If lxyB/lxyB) > 4, then cos(B ) > 0.95
- lxyB < lxyD within 3
- Does not form a D* with a soft pion.

-  K total in pb -1

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Fit the 2  in VPDL bins to extract m and purity of tag

- PT(B)

***Bd mixing measurement***

- Measured

- Expected

- Visible Proper Decay Length:

***Charge of B determined from ************ ***
***charge on reconstructed side***
***Opposite B charge from Flavor ***
***Tag ***

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Expected Asymmetry

- Distribution of oscillated and non-oscillated events are function of K-factor,, m
- B not fully reconstructed. Measure
- average k-factor  K = Pt(D0)/Pt(B)

- VPDL resolution

- K-factor

- Reconstruction efficiency
- of jth channel

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

**Notes:**
figure 3 internal conference note.

## 6 Barrels – 4 layers, Double sided 
	except for layers 1 and 3 of the outermost barrels.
Interspersed F disks – double sided 
H disks – single sided, 24 wedges per h-disk

- 	except for layers 1 and 3 of the outermost barrels.
- Interspersed F disks – double sided
- H disks – single sided, 24 wedges per h-disk

-  K readout channels

- Barrel

- F-Disks

- H-disks

***Bd mixing – Decay length resolution***

-  m
-  m

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Flavor Tagging

- ----We have explored ---
- Jet charge, Soft muon, Same side tagging

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Flavor Tagging Definitions

- Flavor tagging merit (D2)

- B meson

- PB+Ptrk

- Ptrel

- Candidate track Ptrk

- Same side Tagging

| Tagger |  | D | D2(%) |
| --- | --- | --- | --- |
| SLT |  |  |  |
| jetQ+SST |  |  |  |

- Jet Charge

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Fitted asymmetry

- Simultaneous fit to D* and D sample to extract m.

- m =  ps-1
- (D*) – Bd contribution ~83%
- (D) – B+ contribution ~76%

- B+D  X

- Muon Tagger

- JetQ+SST

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Bs Mixing

- Very similar analysis to the Bd mixing. Decay mode used: Bs  Ds , Ds

- 

- 

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## For...Bs mixing observation

*S       = signal events *
***D**2**  = tagging power *
*S/B = signal/background *
-  ***t   ** = proper time resolution** *

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Significant Improvements to flavor tagging

- d> (b) ,   d<(b)

***Significant Improvements to flavor tagging***

- Add Secondary Vertex Charge
- Tagging

- Likelihood ratios for variables discriminating between b and b  ptrel.q, svcharge,jetcharge

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## “Proof of principle” – md measurement

*********m******d ******= 0.558+-0.048(stat.) ps******-1***
*********D******2****** = 1.0% (OST Tagging only)***

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Bs mixing limit – Amplitude fit method

- Ideal non-osc/osc number of events as a function of VPDL (x)  Fit for Amplitude A

- Fit for A as a function of ms ( in steps of 1 ps-1)

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Impact parameter resolution and tuning. 

- Tune track errors for data and MC taking taking into account dependence on:
**Track momentum**
**Track angles**
**Silicon detector hit configuration**
**Silicon cluster width**

- Variable scale factor for VPDL resolution (s.– Overall scale factor = 1.10

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Sample composition

| Decay | Sample composition |
| --- | --- |
| Bs→Dsμν | 20.6% |
| Bs→D*sμν | 57.2% |
| Bs→D*0sμν | 1.4% |
| Bs→D*1sμν | 2.9% |
| Bs→DsDsX | 11.3% |
| B0→DsDX | 3.2% |
| B-→DsDX | 3.4% |

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Bs mixing Limit (460 pb-1)

- Expect A=1, for freq = truems,
-                A=0 for freq  truems
-  C.L
- smallest value of ms at which, A+1.645A = 1
- Sensitivity:
- ms value with 1.645A  = 1

- ms >  ps-1
- Sensitivity =  ps-1

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## To be Added...

- Reconstructed candidates = 

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## World averages for md world Bs mixing limit

- ms >  ps-1
- Sensitivity =  ps-1

- ps

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Future Perspectives

- With additional
- Channels and
- Improvements
- In flavor tagging
- ms upto 11 ps-1
- Within reach at
-  fb-1

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Future perspectives

- With increase in bandwidth
- ms upto 18 ps-1

- Addition of hadronic decay
- Modes and Layer + 50 Hz
- Bandwidth ms upto 26 ps-1

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Conclusions and Summary

- Bd mixing measurement
- We can contribute to the Bd mixing measurement in a small way and an important cross check of the measurement in a hadron collider environment. It is mainly important as a validation tool for our flavor tagging.
- Bs mixing measurement
- More statistics
- Improvements in flavor tagging, introduction of electron tagging (Almost ready!), Unbinned likelihood fit
- More decay modes,
-  BsD s e  X
- Addition of Ds  K*K
- Addition of hadronic decay modes
- Addition of Layer0  improvements in impact parameter resolution
- We are excited.... Lots more to come....

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## 

	BACKUP

- 	BACKUP

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Inner Tracker

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## D0 Silicon – RunIIa disks

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005

## Silicon Alignment

- Beauty 2005, Tania Moulik (KU)

- 06/20/2005