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 MCT. We derive analytical formulas for the boundaries of the kinematically allowed regions in the (M_CT_⊥,M_CT_∥) and (M_CT_⊥,MCT) parameter planes and introduce suitable variables D_CT_∥ and DCT 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 DCTmin (or D_CT_∥min). We illustrate our method with dilepton tt̄ events at the LHC.