Measuring masses in semi-invisible final states at electron-positron colliders

Mass measurement of a particle whose decay products including invisible particles is a challenging task at colliders. For a new physics model involving a dark matter candidate N and a Z(2) symmetry that stabilizes it, a typical new process at e(+) e(-) colliders is the pair production e(+) e(-). Y (Y) over bar followed by decay processes Y -> aN and (Y) over bar -> b (N) over bar, where a and b are visible but N is invisible. In this work, we propose a new method to measure the physical masses in this topology by making use of the kinematic equations given by momentum-energy conservation and on-shell conditions. For each event, the solvability of these equations determines a limited region on the trial m(Y)-m(N) plane. The edge of this region can be used to define two variables, m(Y)(edge) and m(N)(edge), whose distributions are utilized to derive the measurement values of m(Y) and m(N). The measurement deviations and uncertainties are also estimated after including detector effects and background contamination.