33 rd international conference in high energy physics (jul 26 th – aug 2 nd , moscow, russia)
DESCRIPTION
Bs Mixing at D0. Tania Moulik (Kansas University) presented by Andrei Nomerotski (Fermilab/Oxford). 33 rd International Conference in High Energy Physics (Jul 26 th – Aug 2 nd , Moscow, Russia). Mass eigenstates are a mixture of flavor eigenstates: - PowerPoint PPT PresentationTRANSCRIPT
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3333rdrd International Conference in High Energy Physics
(Jul 26th – Aug 2nd, Moscow, Russia)
Tania Moulik (Kansas University)
presented by Andrei Nomerotski
(Fermilab/Oxford)
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Mass eigenstates are a mixture of flavor eigenstates:
BH and BL have a different mass and may have different decay width.
m = MH – ML = 2|M12| ,
= H - L = 2|12|
B mixingB mixingB mixingB mixing
BpBqB
BpBqB
L
H
(t)B
B(t)
iΓMiΓM
iΓMiΓM
(t)B
B(t)
22222121
12121111
dtd
i
Time evolution follows the Schrodinger equation
Dominant Diagram for the transition :
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In an Ideal Scenario..In an Ideal Scenario.. In an Ideal Scenario..In an Ideal Scenario..“O
pp
osite
si
gn
”“S
am
e
sig
n”
SSOS
SSOSi NN
NNtA
)(
Oscillations with amplitude = 1.0 andFrequency = ms.
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DZero DetectorDZero DetectorDZero DetectorDZero DetectorSpectrometer : Fiber and Silicon Trackers in 2 T Solenoid Energy Flow : Fine segmentation liquid Ar Calorimeter and PreshowerMuons : 3 layer system & absorber in Toroidal fieldHermetic : Excellent coverage of Tracking, Calorimeter and Muon Systems
Spectrometer : Fiber and Silicon Trackers in 2 T Solenoid Energy Flow : Fine segmentation liquid Ar Calorimeter and PreshowerMuons : 3 layer system & absorber in Toroidal fieldHermetic : Excellent coverage of Tracking, Calorimeter and Muon Systems
SMT H-disks SMT F-disks SMT barrels
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Analysis outlineAnalysis outlineAnalysis outlineAnalysis outline
μ+/e+
-
K+K-
φD-
S
μ(e) B
X00ss BB
Signal Selection Look for tracks displaced from primary vertex in same jet as /electron
Two tracks should form a vertex and be consistent with mass ( K K) or K* mass (K*K KK) KK invariant mass should be consistent with Ds mass
Identify e/ PT (e/) > 2.0 | | (e/) < 1.0/2.0
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Signal SelectionSignal SelectionSignal SelectionSignal Selection
μ (e)+
π -
K+K-
φD-
S
μ(e) B
ν
X
00ss BB
Muons were selected by triggers without lifetime bias
= no online/offline Impact Parameter cuts
Trigger muon can be used as tag muon : gives access to eDs sample with enhanced
tagging purity
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Signal SelectionSignal SelectionSignal SelectionSignal Selection
μ+
π -
K+K-
φ
D-S
μ(e) B
ν
X
PV
LT(DS)
00ss BB
Ds lifetime is used to have non-zero selection efficiency at Interaction Point
Bs can decay at IP and be reconstructed
Eff=30%
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Effect of NeutrinoEffect of NeutrinoEffect of NeutrinoEffect of NeutrinoNeed to correct Decay Length for relativistic contraction need to know Bs momentum
Can estimate Bs momentum from MC (through so called k-factor) at expense of additional uncertaintyk/k uncertainty causes additional smearing of oscillationsOnly few first periods are useful for semileptonic channels Sensitivity at DL=0 is crucial
All above represents the main difference wrt hadronic channels
Need to correct Decay Length for relativistic contraction need to know Bs momentum
Can estimate Bs momentum from MC (through so called k-factor) at expense of additional uncertaintyk/k uncertainty causes additional smearing of oscillationsOnly few first periods are useful for semileptonic channels Sensitivity at DL=0 is crucial
All above represents the main difference wrt hadronic channels
200 micron
# of periods
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Flavor Tagging and dilution calibrationFlavor Tagging and dilution calibrationFlavor Tagging and dilution calibrationFlavor Tagging and dilution calibration
Identify flavor of reconstructed BS candidate using information from B decay in opposite hemisphere. Identify flavor of reconstructed BS candidate using information from B decay in opposite hemisphere.
a) Lepton Tag : Use semileptonic b decay :Charge of electron/muon identifies b flavor
Ds
cos (l, Bs) < 0.8
Bs
e /
b) Secondary Vertex Tag : Search for secondary vertex on oppositeSide and loop over tracks assoc. to SV.
c) Event charge Tag:All tracks opposide to rec. B
Secondary Vertex
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Dilution in Dilution in ΔΔmmdd measurement measurementDilution in Dilution in ΔΔmmdd measurement measurement
Combine all tagging variables using likelihood ratiosBd oscillation measurement with combined tagger
md= 0.5010.030±0.016ps-1
Combine all tagging variables using likelihood ratiosBd oscillation measurement with combined tagger
md= 0.5010.030±0.016ps-1 Combined dilution: εD2=2.48±0.21±0.08 % Input for Bs
measurement
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Bs decay samples after flavor taggingBs decay samples after flavor taggingBs decay samples after flavor taggingBs decay samples after flavor tagging
NBs( ) = 5601 102 NBs( + e) = 1012 62 (Muon tagged)NBs(K*K + ) = 2997 146
NBs( ) = 5601 102 NBs( + e) = 1012 62 (Muon tagged)NBs(K*K + ) = 2997 146
BsDs e X
Ds
Ds K*K
BsDs X
BsDs XDs
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K*K Fit ComponentsK*K Fit ComponentsK*K Fit ComponentsK*K Fit Components
)(0* signalKKDs
)( 0*0*
KKKD
orKD
)(reflectionPKc )( 0*0* KKKKD
(Cabibbo suppressed)
Difficult mode due to K* natural width and mass resolution – larger errors wrt modeDifficult mode due to K* natural width and mass resolution – larger errors wrt mode
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Results of the Lifetime FitResults of the Lifetime FitResults of the Lifetime FitResults of the Lifetime Fit
cKxΔmec
Kxp s
c
Kx
B
oscnoss
sB
s
/15.0)(/
cos D
From a fit to signal and background region:From a fit to signal and background region:Decay Mode cBs (m) cbkg (m)
BsDs X, Ds 4049 6276
BsDs e X, Ds 44429 64518
BsDs X, Ds K*K 40722 54910
BsDs e X
Ds Ds K*K
BsDs X
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Amplitude MethodAmplitude MethodAmplitude MethodAmplitude Method
tmAsymmetry S cosAmplitude fit = Fourier analysis + Maximum likelihood fit
often used in oscillation measurements
If A=1, the Δm’s is a measurement of Bs oscillation frequency, otherwise A=0
tmDA s cos
Need to know dilution (from Δmd analysis)
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Cross-check on BCross-check on BddXXμμDD±±(())Cross-check on BCross-check on BddXXμμDD±±(())
EXACTLY the same sample & taggerAmplitude Scan shows Bd oscillations
at correct place no lifetime bias with correct amplitude correct dilution calibration
Same results for two other modes
EXACTLY the same sample & taggerAmplitude Scan shows Bd oscillations
at correct place no lifetime bias with correct amplitude correct dilution calibration
Same results for two other modes
Amplitude ScanDØ Run II Preliminary
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Measure Resolution Using DataMeasure Resolution Using DataMeasure Resolution Using DataMeasure Resolution Using Data
Ultimately ms sensitivity is limited by decay length resolution – very important issue Use J/ψ→μμ sample
Fit pull distribution for J/ψ Proper Decay Length with 2 Gaussians Resolution Scale Factor is 1.0 for 72% of the events and 1.8 for the rest
Cross-checked by several other methods
Ultimately ms sensitivity is limited by decay length resolution – very important issue Use J/ψ→μμ sample
Fit pull distribution for J/ψ Proper Decay Length with 2 Gaussians Resolution Scale Factor is 1.0 for 72% of the events and 1.8 for the rest
Cross-checked by several other methods
μ
PVJ/ψ vertex
μ
L±σL
DØ Run II Preliminary
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Amplitude Scan of BAmplitude Scan of BssXXμμDDss(())Amplitude Scan of BAmplitude Scan of BssXXμμDDss(())
Deviation of the amplitude at 19 ps-1 2.5σ from 0 1% probability 1.6σ from 1 10% probability
Deviation of the amplitude at 19 ps-1 2.5σ from 0 1% probability 1.6σ from 1 10% probability
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Log Likelihood ScanLog Likelihood ScanLog Likelihood ScanLog Likelihood Scan
ms < 21 ps-1 @ 90% CL assuming Gaussian errorsMost probable value of ms = 19 ps-1
Systematic
Resolution K-factor variation BR (BsDsX) VPDL model BR (BsDsDs)
In agreement with the amplitude scan
Have no sensitivity above 22 ps-1
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InterpretationInterpretationInterpretationInterpretation
Results of ensemble tests:DZero result :
Combined with World (before CDF measurement):
ms(ps-1)
ms(ps-1)
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Impact on the Unitarity TriangleImpact on the Unitarity TriangleImpact on the Unitarity TriangleImpact on the Unitarity Triangle
BeforeBS mixing
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Impact on the Unitarity TriangleImpact on the Unitarity TriangleImpact on the Unitarity TriangleImpact on the Unitarity Triangle
With D0
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Impact on the Unitarity TriangleImpact on the Unitarity Triangle
With CDF
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““Golden” Events for VisualizationGolden” Events for Visualization““Golden” Events for VisualizationGolden” Events for Visualization
Period of oscillations @ 19ps-1
DØ Run II Preliminary
Weigh events using Weigh events using
210
2
log,
sm
eyMSignif
DF sig
# of periods
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Can We See Bs Oscillations By Eye ?Can We See Bs Oscillations By Eye ?Can We See Bs Oscillations By Eye ?Can We See Bs Oscillations By Eye ?
Weighted asymmetry
This plot does not represent full statistical power of our data
Weighted asymmetry
This plot does not represent full statistical power of our data
# of periods
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More Amplitude ScansMore Amplitude ScansMore Amplitude ScansMore Amplitude Scans
New results : Amplitude scans from two additional modesNew results : Amplitude scans from two additional modes
Ds K*K
BsDs (e XBsDs X
Ds
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CombinationCombinationCombinationCombination
Amplitude is centred at 1 now, smaller errorsLikelihood scan confirms 90% CL ms limits: 17-21 ps-1
Data with randomized tagger : 8% probability to have a fluctuation (5% before for mode)Detailed ensemble tests in progress
Amplitude is centred at 1 now, smaller errorsLikelihood scan confirms 90% CL ms limits: 17-21 ps-1
Data with randomized tagger : 8% probability to have a fluctuation (5% before for mode)Detailed ensemble tests in progress
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Add Same Side TaggingAdd hadronic modes triggering on tag muonAdd more data (4-8 fb-1 in next 3 years) with improved detector – additional layer of silicon between beampipe and Silicon Tracker (Layer0) – better impact parameter resolution
Add Same Side TaggingAdd hadronic modes triggering on tag muonAdd more data (4-8 fb-1 in next 3 years) with improved detector – additional layer of silicon between beampipe and Silicon Tracker (Layer0) – better impact parameter resolution
Layer0 has been successfully installed in April 2006• S/N = 18:1 & no pickup noise • First 50 pb-1 of data on tape, first tracks have been reconstructed
Outlook Outlook Outlook Outlook
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SummarySummarySummarySummary
Established upper and lower limits on ms using Bs Ds X mode
Analysis published in PRL 97 (2006) 021802
Combined with two other channels Bs Ds X Bs Ds e X
considerable improvement in sensitivity 14.1 16.5 ps-1, no improvement for ms interval
Looking forward to a larger dataset with improved vertex detectionIf ms is indeed below 19 ps-1 expect a robust measurement with the extended dataset
Established upper and lower limits on ms using Bs Ds X mode
Analysis published in PRL 97 (2006) 021802
Combined with two other channels Bs Ds X Bs Ds e X
considerable improvement in sensitivity 14.1 16.5 ps-1, no improvement for ms interval
Looking forward to a larger dataset with improved vertex detectionIf ms is indeed below 19 ps-1 expect a robust measurement with the extended dataset
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BACKUP SLIDES
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B MesonsB MesonsB MesonsB Mesons
Bu+ B0 Bs
0 Bc+
b
u
b
d
b
s
b
cMat
ter
b
u
b
c
b
s
b
d
An
ti-M
atte
r
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CKM matrix and B mixingCKM matrix and B mixingCKM matrix and B mixingCKM matrix and B mixing
b
s
d
tbVtsVtdVcbVcsVcdVubVusVudV
b
s
d Wolfenstein parametrisation - expansion in .
1)(
1
)(1
23
22
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AiA
A
iA
)21(
)21(
801.0
002.02265.0sin
2
2
029.0018.0
A
c
0 tbtdcbcdubud VVVVVV
itdtdiubub eVVeVV ||||
complex 1
cbcd
tbtd
cbcd
ubud
VV
VV
VV
VV
Why are we interested to study B meson oscillations
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B MixingB MixingB MixingB Mixing
In general, probability for unmixed and mixed decays Pu,m(B) Pu,m(B). In limit, 12 << M12 ( << M) (Standard model estimate and confirmed by data), the two are equal.
)cos1(2
)(
)cos1(2
)(
/
/
mte
BBp
mte
BBp
t
t
~ 10-4 for Bs system
~ 10-3 for Bd system
310~
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Constraing the CKM Matrix from Constraing the CKM Matrix from mmss
Constraing the CKM Matrix from Constraing the CKM Matrix from mmss
2*22
22
2
2
6tdtbBQCD
W
ttb
Fd VVfB
m
mFmm
Gm
ddB
cbts VV
from Lattice QCD calculations)
Ratio suffers from lower theoreticalUncertainties – strong constraint Vtd
2
2
2
td
ts
Bd
Bs
Bd
Bs
Bd
Bs
d
s
V
V
B
B
f
f
M
M
m
m
And similar expression for ms
CDF+D0 (2006) ms inputs
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Excellent Tevatron PerformanceExcellent Tevatron PerformanceExcellent Tevatron PerformanceExcellent Tevatron Performance
Data sample corresponding to over 1 fb-1 of the integrated luminosity used for the Bs mixing analysis Full dataset is ready (85-90% DAQ efficiency)
Data sample corresponding to over 1 fb-1 of the integrated luminosity used for the Bs mixing analysis Full dataset is ready (85-90% DAQ efficiency)
Run II Integrated Luminosity
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
Apr-02 Jul-02 Oct-02 Jan-03 Apr-03 Jul-03 Oct-03 Jan-04 Apr-04 Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Apr-06 Jul-06
Lu
min
osi
ty (
fb-1
)
Delivered
Recorded
19 April 2002 - 22 February 2006
1.19
1.41
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Muon TriggersMuon TriggersMuon TriggersMuon Triggers
Limitation of data recording. Triggers are needed to select useful physics decay modes. 396 ns bunch crossing rate ~ 2.5 MHz ~50 Hz for data to be recorded.
Single inclusive muon Trigger: |η|<2.0, pT > 3,4,5 GeV Muon + track match at Level 1Prescaled or turned off depending on inst. lumi. We have B physics triggers at all lumi’s
Extra tracks at medium lumi’s Impact parameter requirements Associated invariant mass Track selections at Level 3
Dimuon Trigger : other muon for flavor tagging
e.g. at 50·10-30 cm-2s-1, L3 trigger rate : 20 Hz of unbiased single μ 1.5 Hz of IP+μ 2 Hz of di-μ No rate problem at L1/L2
Limitation of data recording. Triggers are needed to select useful physics decay modes. 396 ns bunch crossing rate ~ 2.5 MHz ~50 Hz for data to be recorded.
Single inclusive muon Trigger: |η|<2.0, pT > 3,4,5 GeV Muon + track match at Level 1Prescaled or turned off depending on inst. lumi. We have B physics triggers at all lumi’s
Extra tracks at medium lumi’s Impact parameter requirements Associated invariant mass Track selections at Level 3
Dimuon Trigger : other muon for flavor tagging
e.g. at 50·10-30 cm-2s-1, L3 trigger rate : 20 Hz of unbiased single μ 1.5 Hz of IP+μ 2 Hz of di-μ No rate problem at L1/L2
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μμ Sample Sampleμμ Sample Sample
μDs: 26,710
Opposite-side flavortagging
Tagging efficiency 21.90.7%
μD±: 7,422
μD±: 1,519
μDs: 5,601±102
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check Using Bcheck Using BddXXμμDD±±(())check Using Bcheck Using BddXXμμDD±±(())
The Amplitude Scan shows Bd oscillations at 0.5 ps-1 no lifetime bias (A=1) : correct dilution calibration
The Amplitude Scan shows Bd oscillations at 0.5 ps-1 no lifetime bias (A=1) : correct dilution calibration
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BS
Se
S tsm
2
)( 2
1
2D2
Detector EffectsDetector EffectsDetector EffectsDetector Effects
flavor tagging power,background
Decay lengthresolution
momentumresolution
p)/p = ? %l = ?
SM prediction - ms ~ 20 ps-1
Trying to measure : Tosc~0.3 X 10-12 s !
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Sample CompositionSample CompositionSample CompositionSample Composition
Estimate using MC simulation, PDG Br’s, Evtgen exclusive Br’s
Estimate using MC simulation, PDG Br’s, Evtgen exclusive Br’s
Signal: 85.6%
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Flavor tag Dilution calibrationFlavor tag Dilution calibrationFlavor tag Dilution calibrationFlavor tag Dilution calibration
Bd mixing measurement using Bd D* X, D* D0 ,
D0 , and evaluate dilution in various diution bins. Follows similar analysis outline as Bs mixing.Form measured asymmetry in 7 bins in visible proper decay length (xM) – Count OS and SS events (compare charge of reconstructed muon with tagger decision)
Fit the 2:
Also include B+ D0 X decay asymmetry.
Bd mixing measurement using Bd D* X, D* D0 ,
D0 , and evaluate dilution in various diution bins. Follows similar analysis outline as Bs mixing.Form measured asymmetry in 7 bins in visible proper decay length (xM) – Count OS and SS events (compare charge of reconstructed muon with tagger decision)
Fit the 2:
Also include B+ D0 X decay asymmetry.
7
12
22
)(
)),((),(
i i
eii
A
mAAm
DD
SSOS
SSOSMi NN
NNxA
)(
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Dilution calibration : ResultsDilution calibration : ResultsDilution calibration : ResultsDilution calibration : ResultsFor final fit, bin the tag variable |d| in 5 bins and do a simultaneuos fit
(i) where i=1,5. Parameters of the fit : m, fcc, 5 Dd, 5 Du = 12
For final fit, bin the tag variable |d| in 5 bins and do a simultaneuos fit
(i) where i=1,5. Parameters of the fit : m, fcc, 5 Dd, 5 Du = 12
mstat.) ps-1
D2 = (2.48 0.21) (%) (stat.)stat.
Incr
easi
ng d
ilutio
n
Incr
easi
ng d
ilutio
n
B0 B+
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Individual Taggers performanceIndividual Taggers performanceIndividual Taggers performanceIndividual Taggers performance
Tagger D (%) D2 (%)
Muon 6.61 0.12
0.473 0.027
1.48 0.17(stat)
Electron 1.83 0.07
0.341 0.058
0.21 0.07 (stat)
SV 2.77 0.08
0.424 0.048
0.50 0.11 (stat)
Total OST
11.14 0.15 2.19 0.22 (stat)
Note :To evaluate the individual tagger performance |dpr| > 0.3
This cut was not imposed for final combined tagger. Final eD2 is higher.
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Likelihood minimization to get Likelihood minimization to get msmsLikelihood minimization to get Likelihood minimization to get msms
Form Probability Density Functions (PDF) for each source Form Probability Density Functions (PDF) for each source
sigisigbgisigcandidates
fff ,,1 FF
fln2Minimize
yMdprxM
xi ppppdxpf prMx
M
M 10log,,
dpr
Dilution Calibration (From md measurement)
Signal selection function (y)
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Bs Signal and backgroundBs Signal and backgroundBs Signal and backgroundBs Signal and background
Signal PDF:
Background PDF composed of long-lived and prompt components – Evaluated from a lifetime fit.
Long Lived Background – Described by exponential convoluted with a gaussian resolution function.
Non-sensitive to the tagging Non-oscillatingOscillating with Δmd frequency
Prompt Background – Gaussian distribution with resolution as fit parameter.
Signal PDF:
Background PDF composed of long-lived and prompt components – Evaluated from a lifetime fit.
Long Lived Background – Described by exponential convoluted with a gaussian resolution function.
Non-sensitive to the tagging Non-oscillatingOscillating with Δmd frequency
Prompt Background – Gaussian distribution with resolution as fit parameter.
)(),,()()(),,( // xgKdxpxKfdKdxp proscnos
sMjjprxMoscnos
j M
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Combine individual tag informations to tag the event.Get tag on opposite side and construct PDF’s for variables discriminating b () and b (+) (Use B+ D0 X decays in data)
Discriminating variables (xi):
Combine individual tag informations to tag the event.Get tag on opposite side and construct PDF’s for variables discriminating b () and b (+) (Use B+ D0 X decays in data)
Discriminating variables (xi):
Combined flavor tag algorithmCombined flavor tag algorithmCombined flavor tag algorithmCombined flavor tag algorithm
more puremore pure
Electron/Muon SV Tagger
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Ensemble TestsEnsemble TestsEnsemble TestsEnsemble TestsUsing data
Simulate Δms=∞ by randomizing the sign of flavour tagging Probability to observe Δlog(L)>1.9 (as deep as ours) in the range 16 < Δms < 22 ps-1 is 3.8% 5% using lower edge of syst. uncertainties band
Using MC Probability to observe Δlog(L)>1.9 for the true Δms=19 ps-1 in the range 17 < Δms < 21 ps-1 is 15%
Many more parameterized MC cross-checks performed – all consistent with above
Using data Simulate Δms=∞ by randomizing the sign of flavour tagging Probability to observe Δlog(L)>1.9 (as deep as ours) in the range 16 < Δms < 22 ps-1 is 3.8% 5% using lower edge of syst. uncertainties band
Using MC Probability to observe Δlog(L)>1.9 for the true Δms=19 ps-1 in the range 17 < Δms < 21 ps-1 is 15%
Many more parameterized MC cross-checks performed – all consistent with above