HEJ 2: High energy resummation for hadron colliders

We present HEJ 2, a new implementation of the High Energy Jets formalism for high-energy resummation in hadron-collider processes as a flexible Monte Carlo event generator. In combination with a conventional fixed-order event generator, HEJ 2 can be used to obtain greatly improved predictions for a number of phenomenologically important processes by adding all-order logarithmic corrections in ($) over cap /p perpendicular to(2). A prime example for such a process is the gluon-fusion production of a Higgs boson in association with widely separated jets, which constitutes the dominant background to Higgs boson production in weak-boson fusion. Program summary Program Title: HEJ 2 Program Files doi: http://dx.doi.org/10.17632/24c9mb6pf9.1 Licensing provisions: GPLv2 or later Programming language: C++ Nature of problem: Conventional event generators for high-energy colliders are based on fixed-order perturbation theory, which converges poorly in regions of phase space with large invariant masses between jets. However, reliable predictions in these regions are of particular importance whenever cuts relevant to weak-boson fusion or weak-boson scattering are applied. One highly relevant example is the separation of gluon fusion and weak-boson fusion contributions to the production of a Higgs boson in association with two or more jets. Solution method: The perturbative description can be amended by resumming the high-energy logarithms associated with large invariant masses to all orders in perturbation theory. HEJ 2 implements this resummation following the High Energy Jets framework. Using HEJ 2 in conjunction with a conventional event generator allows one to obtain reliable predictions for processes involving multiple jets in high-energy regions of phase space. Additional comments including restrictions and unusual features: The current version of HEJ 2 implements multi-jet processes with at most a single Higgs boson in the final state. Matching to fixed-order perturbation theory is currently restricted to leading order. (C) 2019 Elsevier B.V. All rights reserved.