Transverse masses and kinematic constraints: from the boundary to the crease

Understand

We re-examine the kinematic variable m_T2 and its relatives in the light of recent work by Cheng and Han.

• Their proof that m_T2 admits an equivalent, but implicit, definition as the `boundary of the region of parent and daughter masses that is kinematically consistent with the event hypothesis' is far-reaching in its consequences.
• We generalize their result both to simpler cases (m_T, the transverse mass) and to more complex cases (m_TGen).
• We further note that it is possible to re-cast many existing and unpleasant proofs (e.g.