Measurement of the underlying event activity using charged-particle jets in proton-proton collisions at sqrt(s) = 2.76 TeV

TL;DR

This paper measures the underlying event activity in proton-proton collisions at 2.76 TeV using charged-particle jets, analyzing multiplicity and transverse momentum distributions to improve understanding and modeling of UE dynamics.

Contribution

It provides the first detailed measurement of UE activity at 2.76 TeV and compares results with models and previous energies to refine UE modeling.

Findings

UE activity increases with jet transverse momentum

Measurements agree with some Monte Carlo models

Provides constraints for improving UE simulations

Abstract

A measurement of the underlying event (UE) activity in proton-proton collisions is performed using events with charged-particle jets produced in the central pseudorapidity region (abs(eta[jet]) < 2) and with transverse momentum 1<= pt[jet] < 100 GeV. The analysis uses a data sample collected at a centre-of-mass energy of 2.76 TeV with the CMS experiment at the LHC. The UE activity is measured as a function of pt[jet] in terms of the average multiplicity and scalar sum of transverse momenta (pt) of charged particles, with abs(eta) < 2 and pt > 0.5 GeV, in the azimuthal region transverse to the highest pt jet direction. By further dividing the transverse region into two regions of smaller and larger activity, various components of the UE activity are separated. The measurements are compared to previous results at 0.9 and 7 TeV, and to predictions of several Monte Carlo event generators, providing constraints on the modelling of the UE dynamics.