BS Mixing at Tevatron

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BS Mixing at Tevatron

• Donatella Lucchesi
• University and INFN of Padova
• On behalf of the CDFD0 Collaborations

First Workshop on Theory, Phenomenology
and Experiments in Heavy flavour physics May
29-31 2006, Capri, Italy
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Bs Mixing in The Standard Model
Big uncertainties
In the ratio uncertainties cancels
(M. Okamoto, hep-lat/0510113)
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Measurement Principle in a Perfect World
Rather than fit for frequency perform a Fourier
transform
Bs vs. Bd oscillation
B lifetime
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Road Map to ?ms Measurement
Opposite Side
fragmentation particle ?, K
1. Final state reconstruction
?,K
3. Tag B flavor at production time
2. High resolution on proper decay length
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Adding all the realistic effects
Proper time resolution
Flavor tagging power
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Road Map to ?ms Measurement
Opposite Side
fragmentation particle ?, K
1. Final state reconstruction
?,K
3. Tag B flavor at production time
2. High resolution on proper decay length
measure efficiency ? and dilution D ?D2 gives
the effective number of events
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Triggers Used
CDF Two tracks displaced from PV

• D0
• Single inclusive muons
• Ptgt3,4,5 GeV
• Dimuons
• Other muon for
• flavor tagging

• 48 ?m
• includes
• 33 ?m of
• beam spot

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Bs Data sample
Signal Bs?Ds? Ds ???
Bs?Ds? Ds ??? ??KK Ds ?K0K K0 ?K? Ds
?3? Bs?Ds3? Ds ??? Ds ?K0K
Partially reconstructed B mesons
B0 ?D-?
Combinatorial background
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CDF Hadronic Bs yields summary
B ?D0? 26,000
B0 ?D-? 22,000
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CDF Semileptonic samples
Bs?DslX Ds ??? ??KK Ds ?K0K K0 ?K? Ds
?3?
Dsl 53,000
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D0 Semileptonic samples
Decay channel Bs??Ds-X Ds-???- and ??KK-
NBs 26,710 556(stat)
?D-
?Ds-
Cuts selected maximize
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Road Map to ?ms Measurement
Opposite Side
fragmentation particle ?, K
1. Final state reconstruction
?,K
3. Tag B flavor at production time
2. High resolution on proper decay length
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Proper decay time reconstruction

• Fully reconstructed events ct LxyBMB/PtB

• Semileptonic decay ct LxylDMB/PtlD?K

D0 K?PtlD/PtB?
CDF K?PtlD/PtB?LxyB/LxylD?

• It is needed to
• Measure the lifetime to establish the time scale
• Determine the time resolution

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B Lifetime measurement
Central value c?(Bs)404-416 ?m
c?(Bs)1.5380.040(stat) ps
Statistical error 10 ?m
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Proper time resolution, ?t

• Lifetime measurement not very sensitive
• In the ?ms fit each event weighted by its
  resolution
• Dedicated calibration needed

J/????- sample
Prompt Charm track sample
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Proper time resolution, ?t
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Road Map to ?ms Measurement
Opposite Side
fragmentation particle ?, K
1. Final state reconstruction
?,K
3. Tag B flavor at production time
2. High resolution on proper decay length
measure efficiency ?, dilution D ?D2 gives the
effective number of events
2Pright-1
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Opposite Side Taggers

• Use data to calibrate the taggers and to
  evaluate D
• Fit semileptonic and hadronic Bd sample to
  measure D, ?md

• lepton (electron or muon)
• Secondary Vertex
• Event Charge

N 5601 102 (stat)
Tags combined
?D-
?Ds-
0.08
?D2 2.48?0.21(stat.) (syst.)
-0.06
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Same Side Tagger
B0/B likely to have ? nearby
B0s likely to have K
Use PID to separate pion from kaon
Tune Monte Carlo to reproduce B0,B- distributions
then apply to Bs
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Flavor Taggers performances

• Exclusive combination of tags in OST
• SSTK-OST combination assumes independent tagging
  
• information

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Amplitude Scan notation

• A is introduced

• A1 when ?msmeasured ?mstrue

• In the figure
• Points A?(A) from Likelihood
• fit for different ?m
• Yellow band A1.645?(A)
• Dashed line 1.645?(A) vs. ?m
• ?m excluded at 95 C.L.
• if A1.645?(A)lt1
• Measured sensitivity
• 1.645?(A)1

B0 mixing in hadronic decay
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D0 Results
?m?19 ps-1 A/?A2.5 and A-1/?A1.6
favored value 19 ps-1
17lt?mslt21 ps-1 at the 90 C.L.
Sensitivity 14.1ps-1 ?msgt14.8 at the 95 C.L.
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Choice of Procedure
Before un-blinding p-value probability that
observed effect is due background fluctuation.
No search window.
p-valuelt1?
lnL(A1)/lnL(A0)
yes
no
make double sided confidence interval from
?(ln(L)), measure ?ms
set 95 C.L. based on Amplitude Scan
Probability of random tag fluctuation estimated
on data (randomized tags) and checked with toy
Monte Carlo
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CDF Amplitude Scans
Sensitivity 17.3 ps-1 Dmsgt 15.9 ps-1 _at_ 95 CL
Sensitivity 25 ps-1 Dmsgt 16.7 ps-1 _at_ 95 CL
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CDF Combined Amplitude Scan
Sensitivity better than the W.A. 20.1 ps-1 Rare
case!!
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Likelihood Profile significance
Probability of fake p-value0.5
How often random tags produce a likelihood deep
this dip?
Measure ?ms !!!
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Measurement of ?ms
17.00 lt ?ms lt17.91 ps-1 at 90 C.L.
16.94 lt ?ms lt17.97 ps-1 at 95 C.L.
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Vtd/Vts Determination

• Used as inputs
• mBs/mBd 0.9830 PDG 2006
• ?2 1.2100.47 (M. Okamoto, hep-lat/0510113)
• ?md 0.5070.005 PDG 2006

-0.35
Latest Belle result b?s? (hep-ex/050679)
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Conclusions

• 1 fb-1 of data used for Bs oscillation study
• D0
• 2.5s deviation from 0 in the Amplitude Scan
• at ?ms19 ps-1
• 90 C.L. interval for ?ms 17-21 ps-1
• For the summer
• Include Ds?KK, Ds?KsK Ds?3? and eDs
• Include hadronic decays
• Include Same Side Tagging

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Conclusions contd

• CDF
• experimental signature for Bs-Bs oscillations
• Probability of random fluctuation is 0.5
• First direct measurement of

• Future
• Include other decays (Partially recon.
  Ds?Ds?/?)
• Combine efficiently flavor tags
• Improve ct resolution

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BACKUP
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The Accelerator
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Detector for the measurement CDF
Trigger displaced tracks (SVT) Tagging
Power TOF dE/dX (COT) Proper time
Resolution SVX and L00
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Detector for the measurement D0
Fine segmentation Liquid Ar Calorimeter
Preshower
Fiber and Silicon trackers in 2T Solenoid
field
Three layers system absorber
Hermetic detector
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Tevatron Luminosity
1fb-1
Used in the analysis
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Parametrizing tag decision
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Calibrating SSTK
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Calibrating SSTK
Tune MC to reproduce B0/ dilution and then
measure it for SSTK
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D0 Procedure
Correction factor due to missing neutrino

• Several effects taken into account
• Resolution scale factor for detector mismodeling
• Reconstruction efficiency as function of decay
  length
• Physical and combinatorial background
  contributions

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Systematic Uncertainties Amplitude Scan
Related to absolute value of A important when
setting a limit Cancel out in A/?A Very small
compared to statistical error
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Combined Amplitude Scan an other view
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Systematic Uncertainties on ?ms
Fit Model negligible
Relevant only lifetime scale