long decay chains will occur when a heavy new particle is produced. For decays involving coloured particles, hard quantum chromodynamic (QCD) radiation at each step in the decay chain will alter the structure of the event and therefore the number of events passing experimental selection criteria. The effects of radiation are also important in models with degenerate new particle mass spectra, where decay chains are typically limited to one step. Searches for these compressed spectra scenarios look for events in which hard radiation in the initial-state shower recoils against missing transverse energy in the final state to give an observable signal[^1]. The emission of hard QCD radiation in the decay of new particles could either enhance or reduce this effect and so must be taken into account. Therefore, accurate simulation of hard radiation in the decays of BSM particles is necessary in order to optimise searches for new physics.

Monte Carlo event generators use fixed-order matrix elements combined with parton showers and hadronization models to simulate particle collisions. In the  event generator [@Bahr:2008pv; @Arnold:2012fq], the decays of unstable fundamental particles are treated separately from the hard process which produced them, prior to the parton shower phase, using the narrow width 