Observation of B 0 s – B 0 s Oscillations

Observation of B0s – B0

s OscillationsThe 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

Results presented today are contained in two papers:

A. Abulencia

et al. (

CDF Collaborat

ion)

Phys. Rev. L

ett. 97 062003 (2

006)

A. Abulencia

et al. (

CDF Collabo

ration)

hep-ex

/0609040, ac

cepted

by PRL

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


Two-State Quantum Mechanical System

• Produce flavor states:

• Common decay modes ! 2-state QM systemM. Gell-Mann & A. Pais, Phys. Rev., 97, 1387 (1955)

• States with mass & lifetime (neglecting CP violation)

“Light” (CP-even)

“Heavy” (CP-odd)


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


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“Signal” israndom fluctuationis 0.2%

Under signalhypothesis:measure ms

V. M. Abulencia et al., Phys. Rev. Lett.Vol. 97, 062003 (2006)


Since then CDF has focused on turningevidence (3) into an observation (>5)

Use the same 1 fb-1 data set with improved analysis

Tevatron hasdelivered 2 fb-1

CDF has collected 1.6 fb-1

this analysis


Why is this Interesting?

Flavor oscillations occur through2nd order weak interactions e.g.

All factors known well except “bag factor” £ “decay constant”

From measurement of ms derive |V*tbVts|2

C. Gay, Annu. Rev. Nucl. Part. Sci. 50, 577 (2000)

Calculated on lattice, uncertainty ~ 10%


B Meson Flavor Oscillations (cont)

Measure ms ! ms/md

Theoretical uncertainties reduced

Ratio measures |Vtd/Vts|This is why ms ishigh priority in Run II

Well measured:md = 0.507 § 0.005 ps-1 (1%) (PDG 2006)

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


Slide giving example of new physics


Experimental Steps for Measuring Bs Mixing

1. Extract B0s signal – decay mode must identify b-flavor at decay (TTT)

Examples:

2. Measure decay time (t) in B rest frame (L = distance travelled) (L00)

3. Determine b-flavor at production “flavor tagging” (TOF)

“unmixed” means production and decay flavor are the same

“mixed” means flavor at production opposite flavor at decay

Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability


Schematic of Oscillation Event

opposite-side K–

jet charge


Key Experimental Issuesflavor tagging power,

backgrounddisplacement

resolutionmomentumresolution

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


What’s Special About CDF & Tevatron

Tevatron delivered required luminosity

Unique trigger (SVT)

made kaon identification possiblehigh efficiency, high purity flavor tag

Inner layer of silicon (L00)

large sample of completely reconstructed Bs Crucial for lifetime resolution & background reduction

provided decay distance resolution

Detector for particle identification (TOF)


Semileptonic

B0s Decay Modes

•Fully reconstructed (, 0) better decay time resolution•Lower statistics•Signal 8,700

•Not fully reconstructed poorer decay time resolution•Higher statistics•Signal 61,500

Hadronic

}•{

• }{Majority of signal collected with displaced track trigger


Example: Fully Reconstructed Signal

Cleanest decay sequence

Four charged particles infinal state: K+ K- + -

Also use 6 body modes:


Semileptonic Signals


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


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


Determination of |Vtd/Vts|

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

CDF


Summary of CDF Results on B0s Mixing

Observation of Bs Oscillations and precise measurement of ms

Precision: 0.7% Probability of random fluctuation: 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)


Backup & Alternate 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

Documents

Observation of B 0 s – B 0 s Oscillations