  The production of invisible particles plays great importance in high energy
physics. Large part of interesting electroweak processes include production of
neutrinos, while many new physics scenarios predict the existence of similarly
weakly-interacting particles. In events with associated production of invisible
particles and hadronic jets, the measurement of the imbalance in transverse
momentum of the final state particles is the major leverage to reject the
otherwise dominant source of backgrounds in hadron colliders, i.e. the generic
production of many jets by QCD interactions. Here we discuss a novel technique
which utilizes the information derived from the spectrometer, eventually
coupled with the more straightforward calorimeter information, to infer the
passage of invisible particles. We check the validity of this technique in data
and Monte Carlo simulations in a broad range of topologies, starting from the
simplest, with two jets in the final state, to the ones with very large jet
multiplicities. We also suggest a new way, based on the same approach, to
measure the yields and model the kinematics of the QCD multijet background in
invisible particles plus jets signatures. The results are derived using data
collected with the CDF II detector; we argue that the application to LHC
experiments is straightforward.
