Post on 22-Feb-2016
description
BS Mixing at TevatronDonatella Lucchesi
University and INFN of Padova On behalf of the CDF&D0 Collaborations
First Workshop on Theory, Phenomenology andExperiments in Heavy flavour physics
May 29-31 2006, Capri, Italy
Donatella Lucchesi 2May 31, 2006
Bs Mixing in The Standard Model12 12
* *12 122M M iHM M
, 12 1222Im( ) iH L M, 12 122Re( ) iH LM M M
/ 2
/ 2
m
12
1( )L H
L H
)()(
2)()(
tBtBiM
tBtB
dtdi
In the ratio uncertainties cancels:
2
22
2
2
2
2
td
ts
Bd
Bs
td
ts
BdBd
BsBs
Bd
Bs
d
s
V
Vmm
V
VBfBf
mm
mm
= 1.21+0.02+0.035-0.014
(M. Okamoto, hep-lat/0510113)
Big uncertainties
Donatella Lucchesi 3May 31, 2006
Measurement Principle in a Perfect World
))cos(1(21)(
0)(
0tmetP q
t
BB qq
)cos( tmNNNNA smixnomix
mixnomix
Bs vs. Bd oscillation
B lifetime
Rather than fit for frequencyperform a ‘Fourier transform’
ms [ps-
1]
A
Donatella Lucchesi 4May 31, 2006
Road Map to ms Measurement
1. Final state
reconstruction
2. High resolution on proper decay length
T
pL
T
Bct p
ctpm T
xy
3. Tag B flavor at
production time
Opposite Sidefragmentationparticle: , K…
,K
Donatella Lucchesi 5May 31, 2006
Adding all the realistic effects
Proper time resolution
T
pL
T
Bct p
ctpm
T
xy
Flavor tagging power
Donatella Lucchesi 6May 31, 2006
Road Map to ms Measurement
1. Final state
reconstruction
2. High resolution on proper decay length
T
pL
T
Bct p
ctpm T
xy
3. Tag B flavor at
production time
Opposite Sidefragmentationparticle: , K…
,K
measure efficiency and dilution D: D2 gives the “effective” number of events
Donatella Lucchesi 7May 31, 2006
Primary Vertex
Secondary Vertex
d = impact parameter
B
Decay
Le
ngthL
~ 48 mincludes 33 m ofbeam spot
Triggers UsedCDF:Two tracks displaced from PV
D0: Single inclusive muons
o Pt>3,4,5 GeV Dimuons:
o Other muon for flavor tagging
Donatella Lucchesi 8May 31, 2006
Bs Data sample
BsDs Ds KK Ds K*0K K*0 K Ds 3BsDs3 Ds Ds K*0K
Signal BsDs Ds
Partially reconstructed B mesons
Combinatorial backgroundB0 D-
Donatella Lucchesi 9May 31, 2006
CDF Hadronic Bs yields summaryDecay channel YieldBsDs Ds 1570±4
3BsDs Ds K*0K 857±32BsDs Ds 3 612±37BsDs3 Ds 493±37BsDs3 Ds K*0K 204±26Total 3736±7
9B+ D0 ~ 26,000 B0 D- ~ 22,000
Donatella Lucchesi 10May 31, 2006
CDF Semileptonic samples
BsDsX Ds KK Ds K*0K K*0 K Ds 3
Ds~ 53,000
Donatella Lucchesi 11May 31, 2006
Decay channel:Bs+Ds
-XDs
-- and K+K-
Cuts selected maximizeBSS /
NBs = 26,710 ± 556(stat)
+D- +Ds-
D0 Semileptonic samples
Donatella Lucchesi 12May 31, 2006
Road Map to ms Measurement
1. Final state
reconstruction
2. High resolution on proper decay length
T
pL
T
Bct p
ctpm T
xy
3. Tag B flavor at
production time
Opposite Sidefragmentationparticle: , K…
,K
Donatella Lucchesi 13May 31, 2006
Proper decay time reconstruction
Semileptonic decay ct = LxylDMB/Pt
lDK Fully reconstructed events ct = Lxy
BMB/PtB
CDFK=Pt
lD/PtBLxy
B/LxylD
It is needed to: Measure the lifetime to establish the time scale Determine the time resolution
D0K=Pt
lD/PtB
Donatella Lucchesi 14May 31, 2006
B Lifetime measurement
c(Bs)=1.538±0.040(stat) psCentral value c(Bs)=404-416 mStatistical error ~10 m
Donatella Lucchesi 15May 31, 2006
Proper time resolution, t Lifetime measurement not very sensitive In the ms fit each event weighted by its resolution Dedicated calibration needed
Prompt Charm + track sample J/+- sample
Donatella Lucchesi 16May 31, 2006
Proper time resolution, t
Donatella Lucchesi 17May 31, 2006
Road Map to ms Measurement
1. Final state
reconstruction
2. High resolution on proper decay length
T
pL
T
Bct p
ctpm T
xy
3. Tag B flavor at
production time
Opposite Sidefragmentationparticle: , K…
,K
measure efficiency , dilution D
D2 gives the “effective” number of events
Nright-NwrongNright+NwrongD= = 2right-1
Donatella Lucchesi 18May 31, 2006
+D- +Ds-
N = 5601 ± 102 (stat) -lepton (electron or muon)
- Secondary Vertex - Event Charge
Tags combined
Opposite Side Taggers Use data to calibrate the taggers and to evaluate D Fit semileptonic and hadronic Bd sample to measure: D, md
D2 =2.480.21(stat.) (syst.)% +0.08-0.06
Donatella Lucchesi 19May 31, 2006
Same Side Tagger
B0s likely to have K
B0/B± likely to have nearby
Use PID to separate pion from kaonTune Monte Carlo to reproduceB0,B- distributions then apply to Bs
Donatella Lucchesi 20May 31, 2006
Flavor Taggers performances
Exclusive combination of tags in OST SSTK-OST combination assumes independent tagging information
Donatella Lucchesi 21May 31, 2006
Amplitude Scan notation A is introduced: ))cos(A1(
21)(
0)(
0tmetP q
t
BB qq
A=1 when ms
measured = mstrue
B0 mixing in hadronic decayIn the figure: Points: A±(A) from Likelihood fit for different m Yellow band: A±1.645(A) Dashed line: 1.645(A) vs. m m excluded at 95% C.L. if A±1.645(A)<1 Measured sensitivity: 1.645(A)=1
Donatella Lucchesi 22May 31, 2006
D0 Results
“favored value’’ = 19 ps-1 17<ms<21 ps-1 at the 90% C.L.
m19 ps-1 :A/A=2.5 and A-1/A=1.6
Sensitivity = 14.1ps-1
ms>14.8 at the 95% C.L.
Donatella Lucchesi 23May 31, 2006
Choice of Procedure Before un-blinding: p-value probability that observed effect is due background fluctuation. No search window.
p-value<1%?
make double sided confidence interval from (ln()), measure ms
set 95% C.L. basedon Amplitude Scan
yes noln[(A=1)/ln(A=0)]
Probability of random tag fluctuation estimated on data (randomized tags) and checked with toy Monte Carlo
Donatella Lucchesi 24May 31, 2006
CDF Amplitude Scans
Sensitivity: 17.3 ps-1
ms> 15.9 ps-1 @ 95% CL Sensitivity: 25 ps-1
ms> 16.7 ps-1 @ 95% CL
Donatella Lucchesi 25May 31, 2006
CDF Combined Amplitude Scan
Sensitivity betterthan the W.A.20.1 ps-1
Rare case!!
Donatella Lucchesi 26May 31, 2006
Likelihood Profile & significance
How often random tags produce a likelihood deep this dip?
Probability of fake: p-value=0.5% Measure ms !!!
Donatella Lucchesi 27May 31, 2006
Measurement of ms
ms =17.33+0.42 ± 0.07 ps-1
-0.21
17.00 < ms <17.91 ps-1 at 90% C.L.16.94 < ms <17.97 ps-1 at 95% C.L.
Donatella Lucchesi 28May 31, 2006
|Vtd|/|Vts| Determination
Used as inputs: mBs/mBd = 0.9830 PDG 2006 2 = 1.210+0.47 (M. Okamoto, hep-lat/0510113) md = 0.507±0.005 PDG 2006-0.35
|Vtd|/|Vts|=0.208 +0.008 (stat.+syst.)-0.007
|Vtd|/|Vts| = 0.199 +0.026 (stat) +0.018 (syst)-0.025 -0.015
Latest Belle result bs (hep-ex/050679):
Donatella Lucchesi 29May 31, 2006
Conclusions 1 fb-1 of data used for Bs oscillation study
D0: 2.5 deviation from 0 in the Amplitude Scan at ms=19 ps-1
90% C.L. interval for ms: 17-21 ps-1
o For the summer: • Include DsK*K, DsKsK Ds3 and e+Ds• Include hadronic decays• Include Same Side Tagging
Donatella Lucchesi 30May 31, 2006
Conclusions cont’d CDF: experimental signature for Bs-Bs oscillations Probability of random fluctuation is 0.5% First direct measurement of:
ms =17.33+0.42 ± 0.07 ps-1
-0.21
|Vtd|/|Vts|=0.208 +0.008 (stat.+syst.)-0.007
o Future:• Include other decays (Partially recon. Ds
*Ds/)• Combine efficiently flavor tags• Improve ct resolution
Donatella Lucchesi 31May 31, 2006
BACKUP
Donatella Lucchesi 32May 31, 2006
The Accelerator
Donatella Lucchesi 33May 31, 2006
Detector for the measurement: CDFTrigger: displaced tracks(SVT)
Tagging Power:TOF & dE/dX (COT)
Proper time Resolution:SVX and L00
Donatella Lucchesi 34May 31, 2006
Detector for the measurement: D0Fiber and Silicon trackers in 2T Solenoid field
Fine segmentationLiquid Ar Calorimeter& Preshower
Three layerssystem & absorber
Hermetic detector
Donatella Lucchesi 35May 31, 2006
Tevatron Luminosity
1fb-1
Used in theanalysis
Donatella Lucchesi 36May 31, 2006
Parametrizing tag decision
Donatella Lucchesi 37May 31, 2006
Calibrating SSTK
Donatella Lucchesi 38May 31, 2006
Calibrating SSTK
Tune MC to reproduce B0/± dilution and then measure itfor SSTK
Donatella Lucchesi 39May 31, 2006
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
Donatella Lucchesi 40May 31, 2006
Systematic Uncertainties Amplitude Scan
Related to absolute value of A important when setting a limitCancel out in A/AVery small compared to statistical error
Donatella Lucchesi 41May 31, 2006
Combined Amplitude Scan: an other view
Donatella Lucchesi 42May 31, 2006
Systematic Uncertainties on ms
Fit Model: negligible
Relevant only lifetime scale