NLO+NLL' accurate predictions for three-jet event shapes in hadronic Higgs decays

Abstract

We present resummed predictions at next-to-leading logarithmic accuracy matched to the exact next-to-leading order results for a set of classical event-shape observables in hadronic Higgs decays, i.e., for the channels $H\to gg$ and $H\to b\bar{b}$. We furthermore consider soft-drop grooming of the hadronic final states and derive corresponding $\text{NLO}+\text{NLL}^\prime$ predictions for the groomed thrust observable. Differences in the QCD radiation pattern of gluon- and quark-initiated final states are imprinted in the event-shape distributions, offering separation power for the two decay channels. In particular, we show that ungroomed event shapes in $H\to gg$ decays develop a considerably harder spectrum than in $H\to b\bar b$ decays. We highlight that soft-drop grooming can substantially alter this behaviour, unless rather inclusive grooming parameters are chosen.