Abstract 
What are we going to measure? 
How do we measure κ 
Signal Templates Upper: The expected distributions of ( cosθ_{l+}, cosθ_{l}) and (cosθ_{b}, cosθ_{bbar}) reconstructed with CDFII detector by the Monte Carlo simulation for dilepton channel candidates in ttbar Monte Carlo (κ=1.0, 0.0 and 1.0). Lower: Fits of the distributions to a 2 dimensional polynomial function.  
 
Background Templates Upper: The expected distributions of ( cosθ_{l+}, cosθ_{l}) and (cosθ_{b}, cosθ_{bbar}) reconstructed with CDFII detector by the Monte Carlo simulation for Background (WW/WZ/ZZ, DrellYan(Z/γ*)>ττ, ee, μμ, W+QCD fake). Middle: 1σ uncertainty of each bin of the distributions Lower: Fits of the distributions to a 2 dimensional polynomial function.  
 
Reconstructed cosθ_{l+}, cosθ_{b} Distribution Cross: Dilepton candidates in data of 5.1 fb^{1} integrated luminosity. Histogram: Expected signal+background distirbution with 1σ uncertainty  
 
Statistic and Systematic Uncertainties on measured κ By performing pseudo experiments, we obtain statistical uncertainty on measured κ as a fucntion of assumed κ. As for systematic uncertainty, we consider uncertainties from Monte Carlo sample statistics, shape of signal/background templates, jet energy scale, initial/final state radiation, parton distribution function, gluon fusion fraction, effect of next leading order and color reconnection.  
Observed (cosθ_{l+}, cosθ_{l}) and (cosθ_{b}, cosθ_{bbar}) Distributions in 5.1 fb^{1} Data Lower: 2 Δ Log(Likelihood) as a function of assumed κ. We observed κ = 0.042 which gives maximum likelihood for observed distributions.  
 
FeldmanCousisns Intervals based on the statistical and systematic uncertainty for measured κ. From this intervals and observed κ = 0.042, we set 68% confidence interval for κ on the assumed Mt=172.5 GeV/c^{2}.  
 
Top Mass Dependence of Confidence Interval for κ We measure 68% confidence interval for κ on assumptions of different top quark mass (167.5, 170.0, 175.0, and 177.5 GeV/c^{2}).  

Results 0.520<κ<0.605 (68% C.L.) or κ = 0.042^{+0.563}_{0.562} for Mt = 172.5 GeV/c^{2} 