Matching and event-shape NNDL accuracy in parton showers

A bstract To explore the interplay of NLO matching and next-to-leading logarithmic (NLL) parton showers, we consider simplest case γ * Higgs-boson decays to $$ q\overline{q} q ¯ gg respectively. Not only should shower NLL accuracy be retained across observables after matching, but for global event-shape two-jet rate, can augment in such a way that it additionally achieves next-to-next-to-double-logarithmic (NNDL) accuracy, first step on route towards general NNLL. As proof-of-concept exploration this question, direct application multiplicative matrix-element corrections, as well simple implementations MC@NLO POWHEG-style matching. We find two straightforwardly bring NNDL also achieved with POWHEG, although particular care is needed handover between POWHEG shower. Our study involves both analytic numerical components touch some phenomenological considerations.