# Quantum Chromodynamics Monte Carlo Tuning Studies in CMS

## TL;DR

This paper presents recent QCD Monte Carlo tuning studies in CMS, introducing new PYTHIA 8 tunes that improve the modeling of jet and underlying event data across various perturbative orders.

## Contribution

It introduces new CMS PYTHIA 8 tunes with consistent PDFs and coupling parameters, validated across multiple measurements and configurations.

## Key findings

- NLO and NNLO PDF-based tunes reliably describe data
- Tunes improve modeling of jet substructure and underlying events
- Validation across diverse measurements confirms robustness

## Abstract

Recent QCD Monte Carlo tuning studies done in the CMS Collaboration are presented. Jet kinematics, jet substructure, and underlying event measurements in top quark pair events are discussed. New CMS PYTHIA 8 event tunes are presented, exploiting Monte Carlo configurations with consistent parton distribution functions and strong coupling parameter values in the matrix element and the parton shower, at leading order (LO), next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). Predictions from PYTHIA8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets. The tunes are validated with a range of different measurements and matrix element-parton shower merged configurations.