  The MATHUSLA detector is a simple large-volume tracking detector to be
located on the surface above one of the general-purpose experiments at the
Large Hadron Collider. This detector was proposed in [1] to detect exotic,
neutral, long-lived particles that might be produced in high-energy
proton-proton collisions. In this paper, we consider the use of the limited
information that MATHUSLA would provide on the decay products of the long-lived
particle. For the case in which the long-lived particle is pair-produced in
Higgs boson decays, we show that it is possible to measure the mass of this
particle and determine the dominant decay mode with less than 100 observed
events. We discuss the ability of MATHUSLA to distinguish the production mode
of the long-lived particle and to determine its mass and spin in more general
cases.
