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⊥ and M_CT∥, 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⊥,M_CT∥) and (M_CT⊥,M_CT) parameter planes and introduce suitable variables D_CT∥ 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 M_CT⊥^max⁡ and D_CT^min⁡ (or D_CT∥^min⁡). We illustrate our method with dilepton tt¯ events at the LHC.