Effects of invisible particle emission on global inclusive variables at hadron colliders

TL;DR

This paper investigates how invisible particle emission and initial state radiation influence measurements of mass scales at hadron colliders, providing resummed calculations and Monte Carlo comparisons for top and gluino pair-production.

Contribution

It extends previous work by including invisible particles and compares resummed and Monte Carlo results for different processes at the LHC.

Findings

Invisible emission has a small effect on top pair production.

Gluino pair production is significantly affected by invisible particles.

Underlying event effects are large but potentially universal.

Abstract

We examine the effects of invisible particle emission in conjunction with QCD initial state radiation (ISR) on quantities designed to probe the mass scale of new physics at hadron colliders, which involve longitudinal as well as transverse final-state momenta. This is an extension of our previous treatment, arXiv:0903.2013, of the effects of ISR on global inclusive variables. We present resummed results on the visible invariant mass distribution and compare them to parton-level Monte Carlo results for top quark and gluino pair-production at the LHC. There is good agreement as long as the visible pseudorapidity interval is large enough (eta ~ 3). The effect of invisible particle emission is small in the case of top pair production but substantial for gluino pair production. This is due mainly to the larger mass of the intermediate particles in gluino decay (squarks rather than W-bosons). We also show Monte Carlo modelling of the effects of hadronization and the underlying event. The effect of the underlying event is large but may be approximately universal.