The Observation of B 0 s – B 0 s Oscillations The CDF Collaboration 1 st St. Ocean City, NJ, Feb....

The Observation of B0s – B0

s Oscillations

The CDF Collaboration

1st St. Ocean City, NJ, Feb. 7, 2003, H2O 350 F

Joseph KrollUniversity of Pennsylvania

DPFWaikiki, HI2 Nov 2006

2 Nov 2006 J. Kroll (Penn) 2

Today’s Results Made Possible byExcellent Tevatron Performance

Tevatron hasdelivered 2 fb-1

CDF has collected 1.6 fb-1

this analysis 1.0 fb-1

Today’s results Reported in 2 papers by A. Abulencia et al. (CDF collaboration):

hep-ex/0609040, accepted by PRL

PRL, 97, 021802 (2006)

see also Parallel session presentations: V. Tiwari (CMU) , J. Miles (MIT)


Two-State Quantum Mechanical System

Common decay modes ! 2-state QM system

Eigenstates of 2-state system (neglecting CP violation)

“Light” (CP-even)

“Heavy” (CP-odd)

mass & width

Antiparticleexists at time t!

Start (t=0) withparticle


Importance of Neutral B Meson OscillationsCabibbo-Kobayashi-Maskawa Matrix

weak mass

fundamental parameters that must be measured

Oscillation frequencies (md, ms) determine poorly known Vtd, Vts

|Vtd/Vts| measures one side of Unitary Triangle

New particles in loops alter expectations test Standard EWK Model


Theoretical uncertainties reduced in ratio:

All factors well known except

from Lattice QCD calculations - see Okamoto, hep-lat/0510113

Limits precision on Vtd, Vts to ~ 10%

PDG 2006

~ 4%


Some History

1986: 1st evidence of B mixing from UA1 C. Albajar et al., PLB, 186, 247 (1987)

1987: Definitive observation of B0 mixing by ARGUS - indicates UA1 must be Bs, heavy top (>50 GeV) - 1989 confirmed by CLEO

1990’s: LEP, SLC, Tevatron - time-integrated meas. establishes Bs mixes - measure time-dependent B0 oscillations

- lower limits on Bs oscillation frequency

2000: B factories improve precision of B0 oscillation frequency

2006: Tevatron discovers Bs oscillations - two-sided 90% CL limit by DØ - 1st measurement of oscillation frequency by CDF - definitive observation of oscillation signal by CDF

H. Albrecht et al., PLB, 192, 245 (1987)

V. M. Abazov et al., PRL, 97, 021802 (2006)

A. Abulencia et al., PRL, 97, 021802 (2006) & hep-ex/0609040, acc. by PRL

This talk


How Do We Measure Oscillation Frequency?

Measure asymmetry A as a function of proper decay time t

“unmixed”: particle decays as particle

For a fixed value of ms, data should yieldAmplitude “A” is 1, at the true value of ms

Amplitude “A” is 0, otherwise

“mixed”: particle decays as antiparticle

Units: [m] = ~ ps-1, ~=1 then m in ps-1. Multiply by 6.582£ 10-4 to convert to eV


Start 2006: Published Results on ms

Results from LEP, SLD, CDF I ms > 14.4 ps-1 95% CL

see http://www.slac.stanford.edu/xorg/hfag/osc/PDG_2006/index.html

Amplitude method:H-G. Moser, A. Roussarie,NIM A384 p. 491 (1997)


April 2006: Result from the CDF Collaboration

Probability that randomfluctuations mimic thissignal is 0.2% (3)

Assuming signal hypothesis: measure ms

A. Abulencia et al., Phys. Rev. Lett., 97, 062003 (2006)

Since then goal has been to observe signal with > 5 significance


Ingredients in Measuring Oscillations

opposite-side K–

jet charge

Decay modetags b flavorat decay

2nd B tags production flavor

Dilution D = 1 – 2ww = mistag probability

Proper decay timefrom displacement (L)and momentum (p)


Key Experimental Issues

Uncertainty onAmplitude

Signal size

Signal toBackground

Proper timeResolution

Production flavorTag performance

efficient tracking, displaced track trigger

excellent mass resolutionParticle identification: TOF, dE/dx

lepton id, Kaon id with TOF

Silicon mounted on beampipe (Layer 00)

Fully reconstructed signal crucial

CDF’s strengths


Improvements that led to Observation

• Same data set (1 fb-1)

• Proper decay time resolution unchanged

• Signal selection– Neural network selection for hadronic modes

– add partially reconstructed hadronic decays

– use particle id (TOF, dE/dx) (separate kaons from pions)• looser kinematic criteria possible due to lower background

– additional trigger selection criteria allowed

• Production Flavor tag– opposite-side tags combined using neural network

• also added opposite-side kaon tag

– neural network combines kinematics and PID in same-side K tag


Example: Fully Reconstructed Signal

Cleanest decay sequence

Also use 6 body modes:

Add partially reconstructed decays:

Hadronic signal increased from 3600 to 8700


Semileptonic Signals

Semileptonic signal increased from 37000 to 61500


Decay Time Resolution: Hadronic Decays

<t> = 86 £ 10-15 s¼ period for ms = 18 ps-1

Oscillation period for ms = 18 ps-1

Maximize sensitivity:use candidate specificdecay time resolution

Superior decay timeresolution gives CDFsensitivity at muchlarger values of ms

than previous experiments


Semileptonics: Correction for Missing Momentum

Reconstructed quantity Correction Factor (MC) Decay Time


Same Side Flavor Tags

Need particle idTOF Critical(dE/dx too)

Charge of K tags flavorof Bs at production

Our most powerful flavor tag:D2 = 4-5%

(Opposite-side tags: D2 = 1.8%)


Results: Amplitude Scan

A/A = 6.1 Sensitivity31.3 ps-1

Hadronic & semileptonic decays combined


Measured Value of ms

- log(Likelihood) Hypothesis of A=1 compared to A=0


Significance: Probability of Fluctuation

Probability ofrandom fluctuationdetermined from data

Probability = 8 £ 108(5.4)

Have exceededstandard thresholdto claim observation

28 of 350 millionrandom trialshave L < -17.26

-17.26


Asymmetry (Oscillations) in Time Domain


Summary of CDF Results on B0s Mixing

Observation of Bs Oscillations and precise measurement of ms

Precision: 0.7% Probability random fluctuation mimics signal: 8£10-8

Most precise measurement of |Vtd/Vts|

A. Abulencia et al., hep-ex/0609040, accepted by Phys. Rev. Lett.

( 2.83 THz, 0.012 eV)

20 year quest has come to a conclusion


Backup Slides


Weakly Decaying Neutral Mesons

Flavor states (produced mainly by strong interaction at Tevatron)


Key Features of CDF for B Physics

• “Deadtime-less” trigger system– 3 level system with great flexibility

– First two levels have pipelines to reduce deadtime

– Silicon Vertex Tracker: trigger on displaced tracks at 2nd level

• Charged particle reconstruction – Drift Chamber and Silicon– excellent momentum resolution: R = 1.4m, B = 1.4T

– lots of redundancy for pattern recognition in busy environment

– excellent impact parameter resolution (L00 at 1.5cm, 25m £ 25m beam)

• Particle identification– specific ionization in central drift chamber (dE/dx)

– Time of Flight measurement at R = 1.4 m

– electron & muon identification


Example of Candidate

candidate

Same-side Kaon tag

Opposite-side Muon tag

Zoom in oncollision pt.


Measuring Resolution in Data

Use large prompt D meson sample CDF II, D. Acosta et al., PRL 91, 241804 (2003)

Real prompt D+ from interaction point

pair with random trackfrom interaction point

Compare reconstructed decay point to interaction point


ime integrated oscillation probability

must measure proper time dependent oscillation to measure ms


Antiparticleexists a time t!

Form asymmetry A(t) = cos(mst)

ms is oscillation frequency


Measure Amplitude versus Oscillation Frequency

Time Domain Frequency Domain

Units: [m] = ~ ps-1. We use ~=1 and quote m in ps-1

To convert to eV multiply by 6.582£ 10-4

2


Key Experimental Issues

flavor tagging power,background

displacementresolution

momentumresolution

mis-tag rate 40% L) ~ 50 m p)/p = 5%


Proper Time & Lifetime Measurement

production vertex25m £ 25 m

Decay position

Decay time inB rest frame

B0s) = 1.??? § 0.0?? ps

(statistical error only)PDG 2006: 1.466 § 0.059 ps


Determination of |Vtd/Vts|

Previous best result: D. Mohapatra et al.(Belle Collaboration)PRL 96 221601 (2006)

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The Observation of B 0 s – B 0 s Oscillations The CDF Collaboration 1 st St. Ocean City, NJ, Feb....

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