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Control sample for ttbar background in dilepton SUSY search

This document outlines a method for constructing a control sample to estimate the ttbar background in dilepton SUSY searches, specifically focusing on events with two opposite-sign leptons and a varying number of jets. The approach involves selecting ttbar events with an increased number of jets, determining which jets result from W decay, and using simulated lepton-neutrino pairs to refine the sample. This method also addresses the challenge of identifying W jets among selected jets through likelihood maximization based on kinematics and flavor-tag information.

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Control sample for ttbar background in dilepton SUSY search

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  1. Control sample for ttbar background in dilepton SUSY search SUSY ttbar background meeting CERN/Phone, 14 February 2011 Glen Cowan, Aftab Alam, Tim Brooks Physics Department Royal Holloway, University of London g.cowan@rhul.ac.uk www.pp.rhul.ac.uk/~cowan ttbar control sample method / 14.2.11

  2. Main idea Considering SUSY search for 2 opposite-sign leptons + n jets E.g. for now consider n = 2 To construct control sample to estimate ttbar background, select ttbar events with: n+2 jets (e.g., 4) and 1 lepton Figure out which two jets came from W decay Replace with simulated lepton-neutrino. ttbar control sample method / 14.2.11

  3. Finding jets from W decay Nontrivial challenge in figuring out which jets came from W. Pick assignment that maximizes likelihood based on kinematics and flavour-tag info: mass terms flavour-tag terms ttbar control sample method / 14.2.11

  4. Finding jets from W decay (2) Likelihood flavour terms involve parametrized distribution of tag weights for light, c and b jets. Works well in cases when the four selected jets actually correspond to the imposed hypothesis, but a substantial fraction of the time, one or more of the b or W jets is missing, replaced e.g. by gluon jet. Can hopefully deal with this by accepting, say, 4 or more jets with looser cuts, finding the jets from the W, replace with simulated leptons, impose final SUSY search cuts and retain in control sample if it then has the desired number of jets. ttbar control sample method / 14.2.11

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