General Method for Determining the Masses of Semi-Invisibly Decaying Particles at Hadron Colliders

We present a general solution to the long-standing problem of determining the masses of pair-produced, semi-invisibly decaying particles at hadron colliders. We define two new transverse kinematic variables M-CT perpendicular to and M-CT parallel to, which are suitable one-dimensional projections of the contransverse mass M-CT. We derive analytical formulas for the boundaries of the kinematically allowed regions in the (M-CT perpendicular to; M-CT parallel to) and (M-CT perpendicular to ,M-CT) parameter planes and introduce suitable variables D-CT parallel to and D-CT to measure the distance to those boundaries on an event per event basis. We show that the masses can be reliably extracted from the end-point measurements of MXCT perpendicular to max and D-CT perpendicular to(max) (or D-CT parallel to(min)). We illustrate our method with dilepton t (t) over bar events at the LHC.