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This study introduces a novel approach to event selection and background identification in high-energy physics experiments, leading to significant improvements in signal accuracy and background rejection. The focus is on optimizing the selection process for events with specific characteristics, such as the presence of b-tags and the direction of boson decay. Key enhancements include refining the distribution of relevant variables and leveraging advanced kinematic techniques for more precise analysis. The research showcases how utilizing these tailored methodologies can enhance the discrimination between signal and background events, particularly in scenarios involving top quark decay and W boson production. Overall, the proposed kinematics fitter offers a robust framework for optimizing event selection procedures and enhancing the overall efficiency of particle physics experiments.
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Single Top Search ~ New Kinematics Fitter for event selection and Wcc background ~ K Nakamura
61.21 9.5 1.9 0.49 3.3 7.02 ---- 0.6 } 20.67 S/B=7.02/96.6=0.07 S/sq(B)=0.71 S/B=15.3/534.5=0.03 S/sq(B)=0.66 improvement
Mlb distribution Mlnb distribution normalized by # of events of CDFnote At least 1 b-tag
Double tag… At least 1 b-tag S+S S+J double tag
W boson direction at the W* rest frame Dominant channel of Wbb background is t-channel like upper right feynman diagram. -> W boson direction is close to p or pbar direction
Signal W W f b f b t t d u d P P u W*- W*+ +Z @ Wstar Rest Frame b b Wbb b b b b u d u d f d u d u P P f + - + - +Z W W @ Wbb Rest Frame
cosfw distribution generator level … w/o acceptance cut simulated
cosfw distribution generator level … w/ acceptance cut simulated
cosfwxQlep distribution We can use this variable for event selection !
lepton direction at the Top rest frame @ Top Rest Frame n n l- l+ f d u f u d t t P P b +Z b Top quark is polarizing the d-type-quark direction at the top rest frame. -> lepton is boosted d-type-quark direction
bb system behavior for the event selection -> bb invariant mass in the Wbb background looks much smaller than signal… -> gluon splitting to bbbar is very soft like ISR. -> distance between bb and W of the Wbb bkg is larger than signal
Ptbb Mbb
Collation of Ptbb and Mbb distribution Signal gen Signal simulated Mbb Wbb gen Wbb simulated Ptbb
gen -2logL simulated Use only signal PDF gen simulated
-2logL vs Mlnb signal ttbar wbb wcc **Shape of distribution is made from pretag sample
Significance S/sqB = 0.80
S-channel single top event @ CM Frame n l t W* b b ambiguity CDFNOTE Selection of bjet from top quark t-channel : tagged jet -> 95% s-channel : tagged jet -> 53% top mass resolution +15 GeV Selection of neutrino Pz solution 30% … no solution Mlnb : for 4 cases This Top Mass constraint gave some bias to Mlnb distribution??
Likelihood Function for neutrino Pz To define a Likelihood as the function of Neutrino Pz 2 solution case 0 or 1 solution case Move three parameters: METx METy PnZ
Likelihood Function for bbbar ambiguity f is the angle of b-jet @ Wstar Rest Frame
Top Specific Correlation Factor gen P – Rec P Rec P p0=2.12 p1=23.3 p2=0.057 p0=1.83 p1=24.8 p2=0.032 p0=1.31 p1=25.0 p2=0.081 From takeuchi-san From takeuchi-san From takeuchi-san Xaxis value of each bin is weighted mean distribution
Mlnb distribution Sim Lev -- top -- other
B-tag Signal W(mu)bb ttbar 64.3% 52.4% 57.2% 45.9% 37.6% 36.5% 29.5% 19.7% 20.9%
-2Log L distribution as the function of PnZ First 6 events…
Likelihood distribution for the case of PnZ=0 Most likely PnZ is really 0 ?? Is this correct??