CMS-PAS-GEN-17-001

CMS-PAS-GEN-17-001
Extraction and validation of a new set of CMS PYTHIA 8 tunes from underlying-event measurements
CMS Collaboration
August 2018

Abstract: A new set of CMS underlying-event tunes is presented for the PYTHIA8 event generator. The tunes use the NNPDF3.1 parton distribution functions at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) order in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are simultaneously fitted to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the global underlying event, to soft multiparton interactions, and to double-parton scattering contributions, as well as for observables measured in various final states, such as multijet, Drell-Yan, and top quark-antiquark pair production. Here the simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, it is shown that predictions obtained with tunes based on NLO or NNLO parton distribution function (PDF) sets can reliably describe minimum-bias and underlying-event data, with a similar level of agreement as predictions from tunes using LO PDF sets.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 80 (2020) 4. The superseded preliminary plots can be found here.

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