Efficient Matrix-Element Matching with Sector Showers

A Markovian shower algorithm based on "sector antennae" is presented and its main properties illustrated. Tree-level full-color matrix elements can be automatically incorporated in the algorithm and are re-interpreted as process-dependent 2 -> n antenna functions. In hard parts of phase-space, these functions generate tree-level matrix-element corrections to the shower. In soft parts, they should improve the logarithmic accuracy of it. The number of matrix-element evaluations required per order of matching is 1, with an unweighting efficiency that remains very high for arbitrary numbers of legs. Total rates can be augmented to NLO precision in a straightforward way. As a proof of concept, we present an implementation in the publicly available VINCIA plug-in to the PYTHIA 8 event generator, for hadronic $Z^0$ decays including tree-level matrix elements through ${\cal O}(\alpha_s^4)$.