- where the z-direction is along the beam pipe and so
- and are the momentum perpendicular to the beam pipe and
- is the mass.
Hadron collider physicists use another definition of transverse mass, in the case of a decay into two particles:
- where is the transverse energy of each daughter, a positive quantity defined using its true invariant mass as:
For massless daughters, where , the transverse energy simplifies to , and the transverse mass becomes
- where is the angle between the daughters in the transverse plane:
A distribution of has an end-point at the true mother mass: . This has been used to determine the mass at the Tevatron.