${\cal{KK}}\text{MC-hh}$: Resummed Exact ${\cal O}(α^2L)$ EW Corrections in a Hadronic MC Event Generator

Abstract

We present an improvement of the MC event generator Herwiri2, where we recall the latter MC was a prototype for the inclusion of CEEX resummed EW corrections in hadron-hadron scattering at high cms energies. In this improvement the new exact ${\cal O}(α^2L)$ resummed EW generator ${\cal{KK}}$ MC 4.22, featuring as it does the CEEX realization of resummation in the EW sector, is put in union with the Herwig parton shower environment. The {\rm LHE} format of the attendant output event file means that all other conventional parton shower environments are available to the would-be user of the resulting new MC. For this reason (and others -- see the text) we henceforth refer to the new improvement of the Herwiri2 MC as ${\cal{KK}}\text{MC-hh}$. Since this new MC features exact ${\cal O}(α)$ pure weak corrections from the DIZET EW library and features the CEEX and the EEX YFS-style resummation of large multiple photon effects, it provides already the concrete path to 0.05\% precision on such effects if we focus on the EW effects themselves. We therefore show predictions for observable distributions and comparisons with other approaches in the literature. This MC represents an important step in the realization of the exact amplitude-based $QED\otimes QCD$ resummation paradigm. Independently of this latter observation, the MC rigorously quantifies important EW effects in the current LHC experiments.