Abstract
Abstract In this work we present the implementation of generators for W and Z bosons in association with two jets interfaced to parton showers using the method. We incorporate matrix elements from the parton-level Monte Carlo program MCFM in the POWHEG-BOX, allowing for a considerable improvement in speed compared to previous implementations. We address certain problems that arise when processes that are singular at the Born level are implemented in a shower framework using either a generation cut or a Born suppression factor to yield weighted events. In such a case, events with very large weights can be generated after the shower through a number of mechanisms. Events with very small transverse momentum at the Born level can develop large transverse momentum either after the hardest emission, after the shower, or after the inclusion of multi-parton interactions. We present a solution to this problem that can be easily implemented in the . We also show that a full solution to this problem can only be achieved if the generator maintains physical validity also when the transverse momentum of the emitted partons becomes unresolved. One such scheme is the recently-proposed MiNLO method for the choice of scale and the exponentiation of Sudakov form factors in NLO computations. We present a validation study of our generators, by comparing their output to available LHC data. Furthermore, we suggest an observable that is very sensitive to the modeling of multi-parton interactions, that may be studied in both W and Z production in association with two jets.
Highlights
Ten years ago, the next-to-leading order (NLO) corrections to W +2-jet and Z+2-jet production at hadron colliders were published [3, 4]
In this work we present the implementation of generators for W and Z bosons in association with two jets interfaced to parton showers using the POWHEG BOX method
Parton level predictions have been successfully compared with experiment [10,11,12,13] and continue to provide a useful benchmark, NLO calculations are most useful when matched with parton showers such as PYTHIA [14, 15] or HERWIG [16, 17], including an implementation of hadronization models, that describe the transition from partons to the observed hadrons
Summary
Our implementation makes use of improved aspects of the POWHEG BOX, that at some point will lead to a new version of the package. The possibility of generating the importance sampling grids by parallel runs. This was not possible with the standard POWHEG BOX version. Without this feature, the generation of the importance sampling grid for the integration becomes a bottleneck for complex processes, where a single processor run requires too much time. For complex processes this is the only practical way to study uncertainties. An improved structure of the generation of the underlying Born kinematics, first introduced in ref. [41], and made available for all processes, which largely increases the generation efficiency
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