Estimation of the mass of the lighter particle emitted in a two body decay reaction

The mass of an elementary particle, produced in a two body decay, can be calculated by knowing the masses and by measuring the momenta of the decaying particle and of one of the two final state particles with its angle of scattering. In this note we describe the technical results of a Monte Carlo simulation code used for the analysis of the behaviour of the upper limit values at 90%90% confidence level of the mass of the unknown particle as a function of the experimental uncertainties of the measured momenta and angle. The results are useful in designing experiments aimed at the determination of the mass of an unknown light particle.