June 2, 2006 CIPANP06 1

The Observation of B0s

Oscillations at the Tevatron

Matthew Jones

Purdue University/CDF

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Fermion Masses• Gauge sector with massless fermions:

• Higgs sector:

• General Higgs-quark couplings:

• Spontaneous symmetry breaking:

diagonalize

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• One of several explanations for CP violation observed in

• If this was the source of CP violation in the kaon system, then large effects should be observed in B decays.

CKM Sector of the Standard Model

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The CKM Matrix

• Unitary 3x3 matrix 4 parameters:

• λ = 0.2272±0.0010 A = 0.809±0.014

• CP violation η≠0

• Need a precise determination of Vtd

Magnitude proportional to the area of this little square...

Already well measured

(most recent results from CKMFitter)

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(0,0)

The Unitary Triangle

• Try to over-constrain its shape:– ACP in B0J/ψK0

S: sin 2β=0.72±0.02

– Length of one side from

– Length of other side from Δmd/Δms...

(1,0)

(ρ,η)

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Last Year’s Unitary Triangle

• Next strong constraint will come from Δms.

(0,0)

(1,0)

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• Quark flavor eigenstates:

• Time dependence:

• CP eigenstates:

• Mass difference: Δm = MH – M L

Mixing

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Time Evolution • QCD produces flavor eigenstates:

• Interference between CP eigenstates

• Decay identifies final quark flavor:

• Fit for Δms using this model, taking into account several experimental limitations.

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Mixing

From lattice QCD

(hep-lat/0510113)

Δmd and masses are well measured

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Contributions from New Physics?

• FCNC suppressed in Standard Model

• Contribution from new physics scenarios:

• Also affects

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Search for Bs Oscillations

• Four steps:– Reconstruct decays– Measure proper decay time precisely– Identify initial flavor state

– Is the data consistent with oscillations at a

given mixing frequency?

• Significance of an observation:

Statistical power reduced by efficiency and mistag fraction (εD2)

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(2003)

Amplitude Scans and Likelihood

Expect A=1 at true Δms

Significance from depth of log-likelihood ratio

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Result from the DØ Experiment

• March 12, Moriond EW 2006

• Result from DØ: 17<Δms<21 ps-1 (90% CL)

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Result from the DØ Experiment

• March 12, Moriond EW 2006

• Result from DØ: 17<Δms<21 ps-1 (90% CL)

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The CDF Detector

Muon systems:CMP CMX CMU

SVX-IICOTTOF

Hadronic EM

Calorimeter

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Signal Reconstruction• Trigger on displaced tracks and look for:

3,700 fully reconstructed

53,000 partially reconstructed

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Limited number of patterns

Cut at |d0|>120 μm

Proper Decay Time• Proper decay time: ct = Lxy M/pT

• Impact parameter trigger lifetime bias

• Efficiency calculated using B Monte Carlo and an emulation of the trigger

• Checked using B+J/ψK+

lifetime resolution

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Lifetime Measurements

Still dominated by statistical uncertainty

World Averages: hep-ex/0603003

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Initial State Flavor Tagging

Two techniques used:• Opposite Side Tag

– QCD produces pairs – Look for decay products of

the other B hadron (eg, leptons)

– Combined effectiveness:

εD2 = 1.5%• Same Side Tag

Dsπ

B decay

primary vertex

D decaySa

me

Sid

eO

pp

osite

Sid

e

Other B decay

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Δmd=0.503±0.065 ps-1 (hadronic)

Δmd=0.497±0.032 ps-1 (semi-leptonic)

Δmd=0.507±0.004 ps-1 (World average)

Cross Checks with B0/B±

• Account for any difference between signal and calibration samples.

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Initial State Flavor Tagging

Two techniques used:• Opposite Side Tag

– QCD produces pairs – Look for decay products of

the other B hadron (eg, leptons)

– Combined effectiveness:

εD2 = 1.5%• Same Side Tag

– Look for particles produced in association with the Bs

Dsπ

B decay

primary vertex

D decaySa

me

Sid

eO

pp

osite

Sid

e

Other B decay

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Same Side Kaon Tag• Local quark flavor

conservation in QCD

• Expect more kaons with Bs mesons

• Kaon charge identifies the initial Bs flavor

• A primary motivation for building TOF detector.

Original estimates based on Pythia (Lund string model):

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• Count charged kaons around B0, B+, Bs:

• Find more kaons produced in association with Bs

• Qualitative agreement with Monte Carlo

Same Side Kaon Tag

CDF Run II Preliminary

CDF Data

Pythia Monte Carlo

K± around B0/B± K± around Bs

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An Exciting Spring:

• March 12: DØ result released at Moriond• March 14: CDF unblinded an analysis

of about 1/3 of the hadronic decay data– Observed evidence for oscillations

• Next few weeks:– Validation of remaining data– Inclusion of semi-leptonic analysis– Establish criteria for quoting a limit or a

measurement

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Unblinded CDF Analysis

Released April 11, presented at FPCP 2006 on April 12.

evidence of oscillations

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Limit or Measurement?

• Probability of statistical fluctuation: 0.5%

• Measure

-6.06

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Constraints on CKM matrix

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• Already limited by input from Lattice QCD

• Contributes 2.9% to ξ

Future Prospects

(3.8%)

From JLQCD Collab. (hep-ph/0307039)

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Statistical uncertainty and extrapolation to small mq/ms

All other uncertainties

mq/ms=0.036

Lattice Input from HPQCD+MILChep-lat/0507015

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Constraints on New Physics

• Several different assumptions about flavor structure of SUSY models– Parameters in some models are constrained– Others are not...

• Correlated with other experimental results on FCNC

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Example: Impact on MFV Scenarios

(2006 CDF result)

(destructive ±/W± interference)

Theory error on

Lunghi, Porod, Vives: hep-ph/0605177

10

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Summary

• Unlikely to be a statistical fluctuation• Next improvements from lattice results...

• Long term future uncertainty: ~1%?• A milestone has been reached in the world-wide

heavy flavor physics program!– But there are still many more

measured to few % at CLEO-c and BES-III

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Fully Reconstructed Bs Yields in 1 fb-1

• All decays contribute but ones with larger S/B contribute more

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Semi-leptonic Lifetimes

• Correct for unreconstructed momentum

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Lepton-Ds Mass Distribution

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Lifetime Resolution

• Measure σct using “prompt B0s” decays:

φK+K-π+

prompt track

prompt Ds

error propagation scale factor

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Lifetime Resolution

• Estimate σ*ct using

event-by-event error propagation

• Apply scale factor• Resolution is still

small compared with expected period of oscillations (100 μm)

(for Δms = 18 ps-

1)

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Systematic Uncertainties on the Amplitude

• Small compared with statistical uncertainty

Hadronic Semi-leptonic

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Systematic Uncertainty on Δms

• Many ways to bias amplitude

• Much harder to bias Δms

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|Vtd| / |Vts| via Penguin Decays

• Compare Br(Bρ) with Br(BK*)• Small branching fractions• Recent result from Belle (hep-ex/0506079):

,s

,Vts*

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Kaons affect SST on B0/B+

• B+ produced in association with π- or K-

• B0 produced in association with π- or K+

• Particle identification improves same side tag for B0 sample

• Agrees with Monte Carlo

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Flavor Tagging Performance

• Rank opposite side tags (no correlations)• Assume same-side and opposite-side are

uncorrelated compute combined

Opposite side tags

(stat. error)

Same side (syst. error)

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Dilution Scale Factor Analysis

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Same Side Kaon Tag• Count K±, π±, p/p around B0, B+, Bs:

• Find more kaons produced in association with Bs

• Qualitative agreement with Monte Carlo

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Same Side Kaon Tag

• Compare predicted dilution on B+ and B0 samples

• Combine TOF+dE/dx• Re-weight Monte Carlo

to assess impact of:– production mechanisms– fragmentation functions– observed K/π around B– P-wave B mesons– TOF + dE/dx modeling– Luminosity

dependence

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• In context of Minimal Flavor Violation scenarios, limited by theory uncertainty

• Some constraints when considering single mass insertion parameters

• Weaker constraints with multiple mass insertions• These are only a few examples... see also

– Carena, et al.: hep-ph/0603106– Ball & Fleischer: hep-ph/0604249– But there are many others

Constraints on New Physics

Lunghi, Porod, Vives: hep-ph/0605177

Foster, Okumura, Roszkowski: hep-ph/0604121

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GFM Single Mass Insertion ParametersF

oste

r, O

kum

ura,

Ros

zkow

ski:

hep-

ph/0

6041

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