Measurement of the dependence of transverse energy production at large pseudorapidity on the hard-scattering kinematics of proton-proton collisions at $\sqrt{s} = 2.76$ TeV with ATLAS

TL;DR

This study investigates how the production of transverse energy at large pseudorapidity in proton-proton collisions correlates with the kinematics of hard scattering, providing insights into underlying event activity and comparing results with Monte Carlo models.

Contribution

It presents the first measurement of the dependence of transverse energy at large pseudorapidity on the hard-scattering kinematics in 2.76 TeV pp collisions using ATLAS data.

Findings

Transverse energy decreases linearly with target proton's longitudinal momentum fraction.

Weak dependence of transverse energy on projectile proton's momentum.

Monte Carlo models qualitatively reproduce trends but underestimate energy levels.

Abstract

The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb$^{-1}$ of $\sqrt{s} = 2.76$ TeV $pp$ collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pseudorapidity downstream of one of the protons, which are reported here as a function of hard-scattering kinematic variables. The hard scattering is characterised by the average transverse momentum and pseudorapidity of the two highest transverse momentum jets in the event. The dijet kinematics are used to estimate, on an event-by-event basis, the scaled longitudinal momenta of the hard-scattered partons in the target and projectile beam-protons moving toward and away from the region measuring transverse energy, respectively. Transverse energy production at large pseudorapidity is observed to decrease with a linear dependence on the longitudinal momentum fraction in the target proton and to depend only weakly on that in the projectile proton. The results are compared to the predictions of various Monte Carlo event generators, which qualitatively reproduce the trends observed in data but generally underpredict the overall level of transverse energy at forward pseudorapidity.