  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.
