Study of the underlying event and color reconnection in tt events at s = 13 Tev

Abstract

For the first part of this work, we introduce an improvement to the transverse plane method to reduce the effect of the hard interactions on the toward or the trans min region, which in principle should increase the sensitivity of these regions to the underlying event. We perform a particle level study to identify class of events — based on the values of the event shape observables — for which these regions are less contaminated by jets from the hard interaction. We applied this method on Z-boson events and on t¯ t events in the dimuon decay channel. For the Z-boson events, we find that the toward region for spherical events is less sensitive to these jets. For the t¯ t events, we also find that the trans-min region for spherical events is less sensitive to these jets. In addition, using the data collected by the ATLAS detector in 2015 and 2016, measurements of observables defined using this method are compared to the prediction of Monte Carlo event generators for the t¯ t di-muon channel. For the second part of this work, we study the sensitivity to color reconnection of observables defined using the spread of charged particles between a pair of jets. We expect that the color field spanned between a pair of color connected partons, would enhance the production of particles between them. Using the t¯ t all hadronic decay channel, with boosted top quarks, we perform a particle level study to test if there is a difference between the distribution of these observables for a pair of color connected and a pair of non color connected jets