A New Herwig7 Underlying Event Tune: from RHIC to LHC Energies

TL;DR

This paper introduces new Herwig7.3 Monte Carlo tunes optimized for a wide range of energies from RHIC to LHC, improving simulation accuracy for minimum bias proton-proton collisions at mid-rapidity.

Contribution

The study develops and validates two new underlying event tunes for Herwig7.3 that perform well across diverse energies, including below 300 GeV, filling a gap in existing tuning strategies.

Findings

New tunes accurately describe RHIC mid-rapidity data.

Significant improvements over default Herwig tune.

Applicable for future RHIC and LHC simulations.

Abstract

We present parameter sets corresponding to new underlying event tunes for the Herwig7.3 Monte Carlo event generator. The existing Herwig tunes are in good agreement with LHC data, however, they are not typically designed for center-of-mass energies below $\sqrt{s}=300$ GeV. The tunes presented in this study can describe mid-rapidity data collected at the nominal RHIC energy of $\sqrt{s }=200$ GeV, as well as higher center-of-mass energies utilized by experiments elsewhere, such as the LHC. The base "New Haven" tune is developed by fitting minimum-bias simulations of proton-proton collisions to mid-rapidity identified hadron and jet data from the STAR experiment. The "Nashville" tune includes a separate set of parameters developed by tuning to Tevatron proton-antiproton data at $\sqrt{s}=300$, $900$ and $1960$ GeV from CDF, and LHC proton-proton measurements from CMS at $\sqrt{s}=7$ TeV, in addition to the STAR measurements. Both new tunes demonstrate significant improvements over the recommended default tune currently included in the latest version of Herwig for minimum bias production. As such, we advocate using these tunes for future simulation studies at mid-rapidity by the experimental collaborations at RHIC (STAR and sPHENIX) and the LHC (ATLAS, ALICE, CMS).