Mass Measurement in Boosted Decay Chains with Missing Energy

We explore a novel method of mass reconstruction in events with missing energy at hadron colliders. In events with sizeable boost factors in the final steps of dual multistage decay chains, the missing energy particles may each be approximately collinear with a visible standard model particle, spanning a narrow "MET-cone." We exploit this collinear approximation, when applicable, to reconstruct the masses of exotica.