Semi-Leptonic Bs Mixing at D

1
Semi-Leptonic Bs Mixing at DØ

• Meghan Anzelc
• Northwestern University
• On Behalf of the DØ Collaboration
• DPF 2006

2
CKM New Physics
Upper-limit on ?ms limits large SM deviations
3
Tevatron and DØ

• DØ Coverage
• Muon system ? lt 2
• Silicon up to ? lt 3
• Fiber Tracker ? lt 2

Muon System
Where ? -ln(tan(?/2))
4
Analysis Outline

• (Standard Procedure)
• Reconstruct decay products
• Determine flavor of Bs at production and decay
• Tells us if Bs oscillated or not
• Measure Bs decay length
• Oscillation probabilities are function of decay
  length
• Other inputs include K factors, sample
  composition, efficiencies, scale factors
• Fit for ?md verify procedure
• Fit for ?ms

5
Tagging Events

• Opposite-side uses decay lepton, jet charge
• Same-side decay lepton charge gives decay flavor

Efficiency
Tagging Power
Dilution
6
Analysis Inputs

• Correct Bs momentum using K factor

• Correct impact parameter uncertainty, sIP
• Tracking estimates sIP ? J/? pull distribution

For correct sIP ? pull width1, centered at 0 Fit
to J/? pull distribution gives SF1.0 for 78,
1.8 for remainder
7
OST Calibration with Bd

• Amplitude Scan shows Bd oscillations
• at correct place ? no lifetime bias
• w/ correct ampl. ? correct dilution calibration

Bd?XµD(?fp)
NBs(fpµ) 5601 ?102
?md 0.506 0.020(stat.) ps-1 WA, Winter 2006
?md 0.507 0.004 ps-1
8
DØ Result
DØ Published Result (Bs?Dsµ?X, Ds?fp)

• First upper-limit on ?ms 17ps-1 lt ?ms lt 21ps-1
  at the 90 confidence level
• PRL 97, 021802 (2006)

9
DØ Result
Excludes large Standard Model deviations at the
95 confidence level
10
Now to Improve

• Adding additional channels
• Improvements at every analysis step
• Flavor tagging and event selection
• K factors
• Resolution Scale Factors
• Detector upgrade additional silicon layer
• Increased integrated luminosity

11
Tagged Bs Samples

• NBs(fpe) 1012 ? 62
• (Muon tagged)
• NBs(KKµ) 2997 ? 146
• NBs(KsKµ) 593 67

Bs?Ds e ? X
Ds ?fp
DØ RunII Preliminary
Bs?Ds µ ? X
Ds ? KK
Bs?Ds µ? X
Ds ?KsK
12
Combined Result

• Using the same dataset and analysis as the
  published result (Bs?Dsµ?X, Ds?fp)
• Combination increases sensitivity by 2.4ps-1

13
Same-side Tagging

• Quark fragmentation ? Bs (Kaon), Bd (pion)
• Charge of Kaon ? flavor of Bs on signal side
• Developing same-side tag, using dE/dx

14
K-factor Studies

• Developing more sophisticated K factors
• Expected 10 improvement

Different µDs mass ranges
15
Scale Factors
Method developed at DELPHI
IP Uncertainty
sIP smaller for higher pT tracks
Scale Factor is pT dependent

• Divide tracks into categories based on hits and
  cluster width
• Fit estimated (pink green) and true (blue, red
  error bars) impact parameter uncertainties
• Ratio ? Scale Factor
• New event-by-event SF additional 6.5 reduction
  in sIP

16
Silicon Layer0

• Added inner silicon layer in May, radius 1.6cm
• Expect 30 increase in SV resolution

17
Outlook

• Have added three semi-leptonic channels
• Have many improvements on the way, greatly
  increasing sensitivity
• Hardware improvement with Layer0
• Additional luminosity in RunIIb

18
Backup Slides
19
Results of the Lifetime Fit

• From a fit to signal and background region

Decay Mode ctBs (mm) ctbkg (mm)
Bs?Ds m n X, Ds ? fp 404?9 627?6
Bs?Ds e n X, Ds ? fp 444?29 645?18
Bs?Ds m n X, Ds ? KK 407?22 549?10
Bs?Ds e n X
Bs?Ds mn X
Ds ?fp
Ds ? KK
20
(No Transcript)