Higher precision mass measurement via the boundary of many-body phase space

We introduce a new method of mass measurement for particles in decay chains. The method relies upon performing a likelihood analysis on the phase space of the decay in its full dimensionality in a Lorentz-invariant formulation. This method is applicable for any decay chain, but we demonstrate it specifically in the case of a four-body final state decay in which one of the final particles is invisible. We directly compare our method to the edge and endpoint method and show that our new method can achieve higher precision with limited statistics.