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A positive-weight next-to-leading order simulation of weak boson pair production

In this article we describe simulations of ZZ, WZ and WW production based on the positive weight next-to-leading-order matching scheme, Powheg, in the Herwig++ event generator. Building on earlier efforts within the Herwig++ framework, the simulation includes a full description of truncated showering effects, required to correctly model soft, wide angle, emissions in angular-ordered parton showers. We utilize simple relations among each of the diboson cross sections, holding to order alpha_S, in constructing the simulation. Spin correlation effects are also included in the decays of the vector bosons at the tree order. A large part of this work is concerned with a full and thorough validation of the simulations through comparisons with alternative methods and calculations.