Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Bs Mixing at CDF
Frontiers in Contemporary Physics
Nashville, May 24 2005
Gavril Giurgiu – for CDF Collaboration
Carnegie Mellon University
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Introduction - Motivation: Constrain the CKM matrix elements
1)1(
2/1
)(2/1
23
22
32
AiA
A
iA
VVV
VVV
VVV
V
tbts
cbcscd
ubusud
CKM
td
- Within the Standard Model, Bd/s mixing provides information on Vtd/s
- Although md is well measured (0.502 0.007ps-1) determination of Vtd is affected by 15% error
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Unitarity Triangle - Unitarity of CKM matrix:
- Knowledge of both Bd and Bs mixing frequencies would provide better constraints on one side of unitarity triangle:
=1.15 0.05 from Lattice QCD0.0
12.0
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Current Bs Status - Bs mixing not observed yet
- Bs oscillates more than 30 times faster than Bd experimental challenge
- At 95% CL lower limit ms > 14.4 ps-1 with sensitivity of 17.8 ps-1
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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B Mixing Phenomenology - Neutral B system:
- Mass eigenstates:
- Oscillation frequency of Bq mesons given by mq = MH-ML
- Lifetime difference HL
- Neglecting , mixing probability after time t is give by:
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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CDF Detector
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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CDF Detector – Schematic View
Plug Calorimeter
1.3 < || < 3.5
Central Tracker (COT)
|| < 1.0 dE/dx for PID
Time of Flight for K/p separationplaced before 1.4 Tesla Solenoid
Electromagnetic andHadronic calorimeters
Silicon Detector
|| < 2.0
Muon Detectors
|| < 1.0
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Silicon Vertex Trigger (SVT) - Silicon Vertex Trigger implemented at Level 2
- Uses silicon detector information and beamline position to
determine the track impact parameter
- Good impact parameter resolution ~ 47 m:
~33 m beam size ~30 m intrinsic SVT resolution
- Trigger on displaced track
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Mixing Analysis Overview - Mixing analysis ingredients:
- Signal reconstruction - Decay time - B flavor at decay - B flavor at production inferred through flavor tagging: - lepton tags - jet charge tags
- Statistical significance of ms measurement:
Tagging
Signal Reconstruction
Decay time resolution
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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SVT Triggers for B PhysicsSemileptonic (partially reconstructed) decays: Bs lepton Ds X - large number of events - decay time resolution degraded due to missing neutrino - triggered by 4 GeV lepton and displaced track with impact parameter |d0|>120 m and |d0|<1 mm
Hadronic (fully reconstructed) decays:
Bs Ds - smaller number of events - good decay time resolution - triggered by two displaced tracks with impact parameter |d0|> 120 m and |d0|<1 mm
d0
d0d0
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Semileptonic Bs Signals - Missing neutrino cannot see Bs mass peak - Use Ds mass peak and (lepton, Ds) charge correlation:
l+D- - right sign combination
l-D- - wrong sign combination
- Decay modes:
Ds ( 4355 94 ) Ds K*K ( 1750 83 )
Ds 3 ( 1573 88 )
- Total of 7000 Bs candidates but ~20% come from “Physics backgrounds”:
B0/+ Ds D
Bs Ds (D / D(s) lepton X)
Bs Ds D(s)
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Semileptonic Bs Signals (cont)
Ds K*K ( 1750 83 ) Ds 3 ( 1573 88 )
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Hadronic Bs Signals - All final state particles reconstructed observe Bs mass peak
- Decay modes:
Ds ( 526 33 ) Ds K*K ( 254 21 )
Ds 3 ( 116 18 )
- Total of 900 Bs candidates
- Satellite peak:
Bs Ds* (Ds* Ds X)
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Hadronic Bs Signals (cont)Ds K*K ( 254 21 )
Ds 3 ( 116 18 )
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Decay Time - Decay time:
- In semileptonic modes missing neutrino is statistically corrected by:
- Hadronic decays do not need correction - Decay time resolution:
Hadronic:
Semileptonic:
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Decay Time Bias - Because: (1) In both hadronic and semileptonic decays the triggers require displaced tracks (2) Bs events are selected based on decay distance cuts the Bs decay time distribution is biased
- Efficiency as function of decay time obtained from Monte Carlo:
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Flavor Tagging - For Bs mixing analysis CDF used 5 opposite side flavor taggers - Tag inferred from opposite side B in event: - muon and electron tag (semileptonic decay of opposite B) - three jet charge tag types:
- displaced vertex- displaced tracks- high pT
- Tagging power given by D2 where is the tagging efficiency
D = 1 – 2 Pmistag is the tagging dilution
Pmistag – mistag probability
- Large dilution (D) means high tagging power
Trigger B meson
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Flavor Tagging (cont)- Dependence of dilution on different quantities enhances tagging power - Dilution of lepton taggers is calculated as function of: - lepton likelihood (probability that lepton is real)
- (transverse momentum of lepton w.r.t jet axis) - Dilution of jet charge tagger is calculated as function of
- the jet charge:
di - displacement of track i w.r.t the primary vertex - Total D2 1.6 % calculated on an inclusive lepton+SVT sample
relTp
Electron tag Muon tag
Jet charge tag
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Tagger Calibration and Measurement of md
- Perform measurement of md - Since we observe B0 oscillations, we can also measure tag dilutions - Analyze hadronic and semileptonic decays of B0 and B+:
B0 D+
B+ D0
B0 J/K*0 B+ J/K+
B0/+ D- l+ X
B0/+ D-* l+ X
B+/0 D0 l+ X
- Event by event predicted dilution (D) - Fit the dilution calibration factor (S) for each of 5 tag types
- Dilution calibration factors are used for the Bs mixing analysis
DSeB
tmDSeBt
dt
1:
)cos(1:/
/0
Event by event dilution
Dilution Calibration Factor
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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md Results - Hadronic: md = (0.503±0.063±0.015) ps-1
- Dilution calibration factors: S(muon) = 0.83±0.10±0.03 S(electron) = 0.79±0.14±0.04 S(vertex) = 0.78±0.19±0.05 S(track) = 0.76±0.21±0.03 S(high pT) = 1.35±0.26±0.02
- Total D2 ~ 1.1%
- Semileptonic: md = (0.498±0.028±0.015) ps-1
- Dilution calibration factors: S(muon) = 0.93±0.04±0.03 S(electron) = 0.98±0.06±0.03 S(vertex) = 0.97±0.06±0.04 S(track) = 0.90±0.08±0.05 S(high pT) = 1.08±0.09±0.09
- Total D2 ~ 1.4%
Muon Tags
World average: md = 0.502 0.007 ps-1
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Lifetime Measurement - As a cross check of analysis framework measure Bs lifetime - Lifetime fit projections in both hadronic and semileptonic modes
- Semileptonic: c(Bs) = 443 10 (stat) xxx (syst) m
- Hadronic: c(Bs) = 479 29 (stat) 5 (syst) m
- Good agreement with PDG 2004: c(Bs) = 438 17 m
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Amplitude Scan Method
- Introduce Fourier coefficient A (amplitude) - Fix m at different test values and fit for A: (Moser et.al., NIMA 384 491)
A 1 for true value of m A 0 away from true value
- Test amplitude method on B0 oscillations by scanning for md in hadronic modes - points: A 1 - yellow band: A 1.645 - dotted line: 1.645 - Yellow band bellow 1 exclusion
at 95% CL
zoom in
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Bs Analysis - Performed “blind” analysis by randomizing the tag decision: tag = tag (-1)event number
- Evaluate sensitivity and systematic uncertainties from “blind” analysis
- Systematic errors evaluated using pseudo-experiments:- include all variables and distributions determined from data
- fit the toy sample with different Likelihood configurations
- use variations in Amplitude (A) and statistical error (A) to derive
the systematic error:
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Semileptonic Amplitude Scan - Measurement is statistics dominated - Main systematic uncertainties from prompt background and from Physics background
Sensitivity: 7.4 ps-1 Limit: ms > 7.7 ps-1
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Hadronic Amplitude Scan - Measurement is statistics dominated - Main systematic errors come from tagger calibration
Sensitivity: 0.4 ps-1 Limit: ms > 0.0 ps-1
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Combined CDF result on ms - After combining semileptonic and hadronic modes:
Sensitivity: 8.4 ps-1 Limit: ms > 7.9 ps-1
- With full Bs momentum reconstruction, hadronic mode will dominate themeasurement at high ms
Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005
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Conclusions
ms limits from CDF:Semileptonic: 7.4 ps-1
Hadronic: 0.0 ps-1 (will become important at high ms with more statistics)
Combined limit: 7.9 ps-1, sensitivity: 8.4 ps-1
Results will substantially improve soon:- Same side Kaon tagger - Improve decay time resolution in hadronic modes- Add more data
Updated analyses expected soon