Subleading colour effects and spin correlations in the PanScales showers

Abstract

In the context of the PanScales parton shower project, I describe two advances in the development of final-state parton showers with controlled logarithmic accuracy. The first (Ref. [1]) involves simple new algorithms to resolve the long-standing issue of incorrect subleading-colour contributions at leading logarithmic (LL) accuracy in dipoleand antenna-type final-state showers, and also enables the PanScales showers to obtain full-colour NLL accuracy for many observables. The second (Ref. [2]) concerns spin correlations, where we propose a spinor-product based implementation of the well-established Collins algorithm. We verify the logarithmic accuracy of the results with separate purely collinear calculations, using novel spin-sensitive jet observables that are of potential interest also for future experimental measurements.