Minimum-Bias and Underlying Event Studies at CMS

TL;DR

This paper investigates the underlying event in proton-proton collisions at CMS, comparing QCD model predictions and emphasizing the need for model tuning at LHC energies.

Contribution

It provides a detailed analysis of underlying event characteristics at CMS and discusses the discrimination of QCD models based on their extrapolation to LHC energies.

Findings

QCD models reproduce Tevatron data accurately

Models differ significantly when extrapolated to LHC energies

Discrimination among models is possible through underlying event measurements

Abstract

The "Underlying Event" at CMS (under nominal and start-up conditions) is studied by examining charged particle and momentum densities in the "transverse" region in charged particle jet production. The predictions of various QCD models with different multiple parton interaction schemes correctly reproduce Tevatron data, however they fail to agree with each other when extrapolated to the LHC energy. The possibility of discriminating among these models is presented. Exploring QCD dynamics in proton-proton collisions at center-of-mass energy of 14 TeV, and the importance of improving and tuning the QCD Monte Carlo models at start-up are also analyzed.