Precision Measurement of Top Quark Electroweak Coupling by Mustapha BIYABI
Explore the angular distributions and kinematic fitting techniques for the precision measurement of top quark electroweak coupling by Mustapha BIYABI in the semi-leptonic channel. Analyze background, apply constraints, and improve measurements for top quark processes.
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Presentation Transcript
Top Quark EW Coupling Precision Measurement Mustapha BIYABI 19 February 2024
Recap Recap For the Semi leptonic channel : ? ?+> t ?, (t > ?+b, ?+> ?+vl), ( ? > ? ?, ? > 2 quark jets) - Explore the Cos( ) between the lepton and the W boson in the channel where : W > ?+vl. - Analyze the background. - Apply a Kinematic Fitting to improve resolution. The aim is to use these variables for background estimation (discriminator between signal and background processes).
Angular Distribution The cosine of the polar angle (cos( )) between the W boson and the lepton, as well as between the lepton and the z-axis : Using reconstructed informations. Angle between lepton and Z-axis : For Top pair production : Single Top production :
Angular Distribution Angle between W and lepton (W frame) For Top pair production : Single Top production :
Kinematic Fitting Kinematic Fitting Kinematic fitting uses physical laws governing a particle interaction or decay to improve the measurements of the process. For Lepton colliders : MarlinKinFit(minimize a 2 under constraints) Based on three concepts: The Fitter Engine: - Sets up the system of equations && solves it. - Manipulates a lists of constraints and fit objects. The Constraint: Takes 4-vectors of fit objects to calculate its own value Can calculate its own derivatives (the 4-vector components of the fit objects). The Fit Object: Encapsulates all details of the parametrization (number of parameters, parametrization).
Covariance Matrix Covariance Matrix The first step to implement such fitting : is to compute the uncertainties for each final state (dE, d?,??) I tried to compute the Covariance Matrix for: - Leptons(muon, electron) Using tracking. - jets.*(little bit complicated). - But !! - First we set different constraints : Momentum-Constraint, Mass Constraint Mass of a W/Z has Breit-Wigner-shape, deviation may be bigger than detector resolution, As solution : - Instead of imposing f(??) = 0 (hard constraint), add term to 2:
Fit Probability Fit Probability The Fit Proba : The Fit Proba : starting form high values of uncertainties. There is an issue at the level of Convergence !!
Neutrino Correction Due to the missing neutrino : the kinematic fitting may not yield the desired results. As Alternative, we can follow one approach to include neutrino correction into the fit. The neutrino momentum : Estimated from the kinematics of the semi-leptonic decay assuming ,the following information is available: Mass (mX ) and flight direction of the mother hadron and the 4-momentum of all visible decay products (l ,Y) originating from the vertex at which the semi-leptonic decay occurs. From which we can compute the vectorial momentum of the neutrino, However flavor tagging is crucial for the - correction.
Background Samples Background Samples + Single Top Production !
Single Top Single Top Bkg Bkg
