KrkNLO matching and alternative PDF factorisation schemes

by James Whitehead

Wednesday 30 Apr 2025, 14:00 → 15:00 Europe/Zurich

5017 (Milano Bicocca)

The consistent combination of perturbation theory and the logarithmic resummation enabled by parton shower algorithms, ‘NLO matching/merging’, is a key tool for LHC phenomenology. Two general methods are in widespread use: MC@NLO and Powheg. Each has advantages, but also disadvantages: negative weights and the dependence on an unphysical shower scale (MC@NLO); exponentiation of the real matrix-element or dependence on a suppression factor (Powheg). The KrkNLO method is an alternative method for NLO matching of colour-singlet processes, which has recently been formulated in maximal applicable generality and automated within Herwig 7. It exploits the freedom to choose a factorisation scheme for PDFs beyond LO to make the matching algorithm especially simple. As a result, it is positive by construction and has no unphysical shower-scale or factor-dependence. In addition to an outline of the KrkNLO method and the associated phenomenology, we summarise recent work on alternative PDF factorisation schemes, exploring the properties of both specific alternatives which have been proposed, and in general.

Zoom: https://cern.zoom.us/j/68870769721?pwd=dzIE3bSnRiTVFm7RD3EQUwODZCys03.1