Parton showering with higher-logarithmic accuracy for soft emissions

The accuracy of parton-shower simulations is often a limiting factor in the interpretation of data from high-energy colliders. We present the first formulation of parton showers with accuracy one order beyond state-of-the-art next-to-leading logarithms, for classes of observable that are dominantly sensitive to low-energy (soft) emissions, specifically non-global observables and subjet multiplicities. This represents a major step towards general next-to-next-to-leading logarithmic accuracy for parton showers.
Comment: 6 pages, 4 figures + supplemental material (+ 5 pages, 3 figures); v2 matches the version published in Physical Review Letters