Abstract
This paper presents new sets of parameters (“tunes”) for the underlying-event model of the {textsc {herwig}} ,7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in {textsc {herwig}} ,7, and are obtained from a fit to minimum-bias data collected by the CMS experiment at sqrt{s}=0.9, 7, and 13 ,text {Te}text {V} . The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the data.
Highlights
The herwig 7 event generator is a multipurpose event generator, which can perform matrix-element (ME) calculations beyond leading order (LO) in quantum chromodynamics (QCD), via the matchbox module [5], matched with parton shower (PS) calculations
The configurations of parton distribution function (PDF) sets in the CH1, CH2, and CH3 tunes allow us to study whether using an NNLO PDF set consistently for all aspects of the herwig 7 simulation, or an LO PDF set for the simulation of multiple-parton interactions (MPI), can both give a reliable description of MB data
Even though a lower value of μ2 would lead to a lower amount of MPI in a given event, the combined effect of the parameters of the CH tunes results in a larger amount of MPI compared with SoftTune
Summary
The herwig 7 event generator is a multipurpose event generator, which can perform matrix-element (ME) calculations beyond leading order (LO) in QCD, via the matchbox module [5], matched with parton shower (PS) calculations. In contrast to SoftTune, the tunes presented here are based on the NNPDF 3.1 PDF sets [18], and use the next-to-next-to-leading-order (NNLO) PDF set for the simulation of the PS, and either an LO or NNLO PDF set for the simulation of MPI and the beam remnants This choice of PDF sets is similar to that used to obtain tunes for the pythia 8 event generator in Ref.
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