A major new release of the Monte Carlo event generator Herwig++ (version 3.0) is now available. This release marks the end of distinguishing Herwig++ and HER-WIG development and therefore constitutes the first major release of version 7 of the Herwig event generator family. The new version features a number of significant improvements to the event simulation, including: built-in NLO hard process calculation for virtually all Standard Model processes, with matching to both angular-ordered and dipole shower modules via both subtractive (MC@NLO-type) and multiplicative (Powheg-type) algorithms; QED radiation and spin correlations in the angular-ordered shower; a consistent treatment of perturbative uncertainties within the hard process and parton showering. Several of the new features will be covered in detail in accompanying publications, and an update of the manual will follow in due course.

A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements over the major version 7.0, notably: multi-jet merging with the dipole shower at LO and NLO QCD; spin correlations in both the dipole and angular-ordered parton showers; an improved choice of evolution variable in the angular-ordered parton shower; improvements to mass effects and top decays in the dipole shower, improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour reconnection; improvements to strangeness production; as well as a new tune of the hadronisation parameters and support for generic Lorentz structures in BSM models. This article illustrates new features of versions 7.1 and 7.2.

We study Higgs pair production with a subsequent decay to a pair of photons and a pair of bottoms at the LHC. We use the log-likelihood ratio to identify the kinematic regions which either allow us to separate the di-Higgs signal from backgrounds or to determine the Higgs self-coupling. We find that both regions are separate enough to ensure that details of the background modeling will not affect the determination of the self-coupling. Assuming dominant statistical uncertainties we determine the best precision with which the Higgs self-coupling can be probed in this channel. We finally comment on the same questions at a future 100 TeV collider.

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We perform a detailed study of the sources of perturbative uncertainty in parton-shower predictions within the Herwig 7 event generator. We benchmark two rather different parton-shower algorithms, based on angular-ordered and dipole-type evolution, against each other. We deliberately choose leading order plus parton shower as the benchmark setting to identify a controllable set of uncertainties. This will enable us to reliably assess improvements by higher-order contributions in a follow-up work.