Eur. Phys. J. C (2018) 78: 244
https://doi.org/10.1140/epjc/s10052-018-5723-2

Regular Article - Theoretical Physics

Merging NLO multi-jet calculations with improved unitarization

¹ IPPP, Department of Physics, Durham University, Durham, UK
² Institute for Theoretical Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany
³ Particle Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, UK
⁴ Particle Physics, Faculty of Physics, University of Vienna, Vienna, Austria

^* e-mail: johannes.bellm@durham.ac.uk

Received: 1 June 2017
Accepted: 9 March 2018
Published online: 21 March 2018

Abstract

We present an algorithm to combine multiple matrix elements at LO and NLO with a parton shower. We build on the unitarized merging paradigm. The inclusion of higher orders and multiplicities reduce the scale uncertainties for observables sensitive to hard emissions, while preserving the features of inclusive quantities. The combination allows further soft and collinear emissions to be predicted by the all-order parton-shower approximation. We inspect the impact of terms that are formally but not parametrically negligible. We present results for a number of collider observables where multiple jets are observed, either on their own or in the presence of additional uncoloured particles. The algorithm is implemented in the event generator Herwig.