Performing an Underlying Event Tune for Proton-Proton Collisions at RHIC using the Herwig 7.3 Event Generator*

We report new parameter sets for the underlying event model used by the Herwig 7.3 Monte Carlo event generator. Unlike existing tunes for Herwig, which are typically designed for LHC experiments and are not suited for center-of-mass collision energies below 300 GeV, the tunes presented here can describe data collected at the nominal RHIC energy of √s = 200 GeV. We develop a base tune by fitting minimum bias simulations of proton-proton collisions to identified hadron spectra and underlying event measurements from the STAR experiment. Furthermore, we obtain a separate set of parameters fit to Tevatron proton-antiproton data at √s = 0.3, 0.9, and 1.96 TeV and CMS proton-proton measurements at √s = 7 TeV, in addition to the STAR measurements. We explore the utility of including jet substructure measurements in improving Herwig's simultaneous description of both the hard and soft particle structure in these collision events. Simulations using each new tune demonstrate improvement over the default tune recommended by Herwig authors for minimum bias production. As such, we recommend using these tunes to simulate data collected by the STAR and sPHENIX experiments at RHIC.