In this talk I give an introduction to the methods involved in calculating differential cross sections at leading order.
A differential cross section with two final-state particles is easy to calculate and usually taught in introductory particle physics lectures.
For a higher number of final-state particles, however, different methods have to be employed, because the calculation of the matrix element with spin sums becomes computationally expensive and the phase space integration is not possible analytically. In this talk, I will present how the calculation of the matrix element is done in practice and how to perform the phase space integration using numerical Monte Carlo methods.
Lastly, I will put the talk in context with an ongoing project on building an NLO Monte Carlo event generator specialized for top quark production at lepton colliders,which will use resonant-aware subtraction to deal with resonant top quarks.
