Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 1 B s Mixing at CDF Frontiers in Contemporary...

Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005

1

Bs Mixing at CDF

Frontiers in Contemporary Physics

Nashville, May 24 2005

Gavril Giurgiu – for CDF Collaboration

Carnegie Mellon University


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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


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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


4

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


5

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:


6

CDF Detector


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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


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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


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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


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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


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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)


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Semileptonic Bs Signals (cont)

Ds K*K ( 1750 83 ) Ds 3 ( 1573 88 )


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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)


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Hadronic Bs Signals (cont)Ds K*K ( 254 21 )

Ds 3 ( 116 18 )


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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:


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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:


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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


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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


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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


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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


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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


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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


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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:


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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


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Hadronic Amplitude Scan - Measurement is statistics dominated - Main systematic errors come from tagger calibration



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Combined CDF result on ms - After combining semileptonic and hadronic modes:


- With full Bs momentum reconstruction, hadronic mode will dominate themeasurement at high ms


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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

Gavril Giurgiu, Carnegie Mellon, FCP Nashville 2005 1 B s Mixing at CDF Frontiers in Contemporary...

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