Event generator tunes obtained from underlying event and multiparton scattering measurements

TL;DR

This paper develops new parameter sets for Monte Carlo event generators to improve modeling of underlying events in proton collisions, using combined data from CMS and CDF experiments across different energies.

Contribution

It introduces new tunes for PYTHIA8, PYTHIA6, and HERWIG++ based on combined fits to diverse experimental data, enhancing predictive accuracy for 13 TeV collisions.

Findings

Improved UE modeling predictions at 13 TeV

Parameter consistency between UE and double-parton scattering fits

Better agreement with minimum bias, multijet, and Drell-Yan data

Abstract

New sets of parameters ("tunes") for the underlying-event (UE) modeling of the PYTHIA8, PYTHIA6 and HERWIG++ Monte Carlo event generators are constructed using different parton distribution functions. Combined fits to CMS UE proton-proton (pp) data at sqrt(s) = 7 TeV and to UE proton-antiproton (p p-bar) data from the CDF experiment at lower sqrt(s), are used to study the UE models and constrain their parameters, providing thereby improved predictions for proton-proton collisions at 13 TeV. In addition, it is investigated whether the values of the parameters obtained from fits to UE observables are consistent with the values determined from fitting observables sensitive to double-parton scattering processes. Finally, comparisons of the UE tunes to "minimum bias" (MB) events, multijet, and Drell-Yan (q q-bar to Z / gamma* to lepton-antilepton + jets) observables at 7 and 8 TeV are presented, as well as predictions for MB and UE observables at 13 TeV.