  In analogy to the transverse mass constructed from two objects, we define the
spatial mass constructed from the input objects 3-vector momenta. This
observable is insensitive to jet mass scale and resolution uncertainties when
constructed from small-radius hadronic jets. Thus it improves the effective
resolution on multijet masses for searches and measurements in hadronic final
states. To illustrate the efficacy of the spatial mass, we consider a top quark
mass measurement at the Large Hadron Collider (LHC) in the 3-jet final state.
The reduction in uncertainty comes with a negligible cost in sensitivity.
