This definition of the transverse mass is used in conjunction with the definition of the (directed) transverse energy E → → T = E p → → T | p → → | = E E 2 − − m 2 p → → T with the transverse momentum vector p → → T = ( p x , p y ) . It is easy to see that for vanishing mass ( m = 0 ) the three quantities are the same: E T = p T = m T . The transverse mass is used together with the rapidity, transverse momentum and polar angle in the parameterization of the four-momentum of a single particle: ( E , p x , p y , p z ) = ( m T cosh ⁡ ⁡ y , p T cos ⁡ ⁡ ϕ ϕ , p T sin ⁡ ⁡ ϕ ϕ , m T sinh ⁡ ⁡ y )