From Particle Flow to Colour Flow in Top Events

A deeper understanding of the underlying event in $t\overline{t}$ pair production is expected to improve the current uncertainty on the measurements of the top quark mass. By selecting events with an electron, a muon and two b-tagged jets a high purity signal is obtained. The main properties of the underlying event are isolated and compared between data and different Pythia Monte Carlo Tunes. Discrepancies between the total number of charged particles for different models is observed. Furthermore a contribution of colour reconnection to the modeling of the average transverse momentum of the charged particles is identified.