Speaker
Description
Parton showers are an essential feature of event generation that provide a numerical resummation of the large logarithms that enhance soft and collinear radiation. Matching them to higher order calculations requires careful treatment in order to avoid double-counting real radiation and preserve fixed order accuracy through matching algorithms such as MC@NLO. As we approach HL-LHC, there is a need for increasing precision of theoretical predictions so the inclusion of NLO EW alongside QCD corrections and matching to a QED shower becomes necessary. QED parton showers present addition complications, including the potential for negative splitting kernels and many more spectators to each splitting. In a dipole implementation, these spectators absorb the recoil required to satisfy momentum conservation and on-shell conditions in each splitting, however this 'reshuffling' of momenta can lead to distortion of the lineshape if it spans a resonance. Thus, the need for a resonance aware implementation is much greater for a QED shower than QCD due to the expanded set of spectators.
I will present the first implementation of automated QCD+EW MC@NLO matching in the event generator Sherpa, along with an approach to treat resonances by factorising the parton shower into production and decay for hard emissions, using Drell-Yan to illustrate the cases of both a neutral and charged resonance.