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We consider SUSY-like events with two decay chains, each terminating in aninvisible particle, whose true energy and momentum are not measured in thedetector. Nevertheless, a useful educated guess about the invisible momenta canstill be obtained by optimizing a suitable invariant mass function. We reviewand contrast several proposals in the literature for such ansatze: fourversions of the M_T2-assisted on-shell reconstruction (MAOS), as well asseveral variants of the on-shell constrained M_2 variables. We compare theperformance of these methods with regards to the mass determination of a newparticle resonance along the decay chain from the peak of the reconstructedinvariant mass distribution. For concreteness, we consider the event topologyof dilepton ttbar events and study each of the three possible subsystems, inboth a ttbar and a SUSY example. We find that the M_2 variables generallyprovide sharper peaks and therefore better ansatze for the invisible momenta.We show that the performance can be further improved by preselecting eventsnear the kinematic endpoint of the corresponding variable from which themomentum ansatz originates.

Testing Invisible Momentum Ansatze in Missing Energy Events at the LHC