of Observation B0s B0s Oscillations
The CDF Collaboration
Joseph Kroll University of Pennsylvania
1st St. Ocean City, NJ, Feb. 7, 2003, H2O 350 F
DPF Waikiki, HI 2 Nov 2006
Results presented today are contained in two papers:
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Parallel session presentations: V. Tiwari (CMU) , J. Miles (MIT)
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Two-State Quantum Mechanical System
Produce flavor states: Common decay modes ! 2-state QM system
M. Gell-Mann & A. Pais, Phys. Rev., 97, 1387 (1955)
States with mass & lifetime (neglecting CP violation)
Light (CP-even) Heavy (CP-odd)
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Antiparticle exists a time t! Form asymmetry A(t) = cos( mst)
s
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m is oscillation frequency
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Measure Amplitude versus Oscillation Frequency
Time Domain Frequency Domain
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Units: [ m] = ~ ps-1. We use ~=1 and quote m in ps-1 To convert to eV multiply by 6.582 10-4
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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 2 Nov 2006 J. Kroll (Penn)
Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997)
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April 2006: Result from the CDF Collaboration
V. M. Abulencia et al., Phys. Rev. Lett. Vol. 97, 062003 (2006)
Probability Signal is random fluctuation is 0.2% Under signal hypothesis:
s
measure m
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Since then CDF has focused on turning evidence (3 ) into an observation (>5 )
Tevatron has
-1
delivered 2 fb CDF has collected 1.6 fb-1 this analysis
Use the same 1 fb-1 data set with improved analysis
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Why is this Interesting?
Flavor oscillations occur through 2nd order weak interactions
C. Gay, Annu. Rev. Nucl. Part. Sci. 50, 577 (2000)
e.g.
From measurement of ms derive |V*tbVts|2
All factors known well except bag factor decay constant Calculated on lattice, uncertainty ~ 10%
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B Meson Flavor Oscillations (cont)
Well measured: md = 0.507 0.005 ps-1 (1%) (PDG 2006) Measure ms ! ms/ md Theoretical uncertainties reduced
Ratio measures |Vtd/Vts| This is why ms is high priority in Run II
from Lattice QCD calculations see Okamoto, hep-lat/0510113
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Slide giving example of new physics
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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
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Schematic of Oscillation Event
jet charge
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Key Experimental Issues
flavor tagging power, background displacement resolution momentum resolution
mis-tag rate 40%
(L) ~ 50 m
(p)/p = 5%
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Whats Special About CDF & Tevatron
Tevatron delivered required luminosity Unique trigger (SVT)
large sample of completely reconstructed Bs Crucial for lifetime resolution & background reduction
Inner layer of silicon (L00)
provided decay distance resolution
Detector for particle identification (TOF)
made kaon identification possible high efficiency, high purity flavor tag
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B0s Decay Modes
Hadronic
{
Semileptonic
}
Fully reconstructed ( , 0) better decay time resolution Lower statistics 8,700 Signal Not fully reconstructed poorer decay time resolution Higher statistics Signal 61,500
{
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}
Majority of signal collected with displaced track trigger
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Example: Fully Reconstructed Signal
Cleanest decay sequence
Four charged particles in final state: K+ K- + Also use 6 body modes:
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Semileptonic Signals
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Proper Time & Lifetime Measurement
Decay position
production vertex 25 m 25 m
Decay time in B rest frame
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0s
( B ) = 1.??? 0.0?? ps (statistical error only) 19 PDG 2006: 1.466 0.059 ps
Decay Time Resolution: Hadronic Decays
Maximize sensitivity: use candidate specific decay time resolution
t -15
< > = 86 10 period for
s -1
s
Superior decay time resolution gives CDF sensitivity at much
s
m = 18 ps
larger values of m than previous experiments
s -1
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J. Kroll (Penn) period for m = 18 ps
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Semileptonics: Correction for Missing Momentum
Reconstructed quantity
Correction Factor (MC)
Decay Time
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Same Side Flavor Tags
Charge of K tags flavor of Bs at production
Need particle id TOF Critical (dE/dx too)
Our most powerful flavor tag: D2 = 4-5% Opposite-side tags: D2 = 1.8%
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Results: Amplitude Scan
A
Sensitivity 31.3 ps
A/ = 6.1
Hadronic & semileptonic decays combined
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Measured Value of ms
- log(Likelihood) Hypothesis of A=1 compared to A=0
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Significance: Probability of Fluctuation
Probability of random fluctuation determined from data 28 of 350 million random trials have L < -17.26 Probability = 8 108 (5.4 ) Have exceeded standard threshold to claim observation
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-17.26
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Asymmetry (Oscillations) in Time Domain
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Determination of |Vtd/Vts|
Previous best result:
D. Mohapatra et al. (Belle Collaboration) PRL 96 221601 (2006)
CDF
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Summary of CDF Results on B0s Mixing
A. Abulencia et al., hep-ex/0609040, accepted by Phys. Rev. Lett.
Observation of Bs Oscillations and precise measurement of ms
Precision: 0.7%
Probability o...