Relativistic momentum
= Relativistic momentum
{title2=$\mathbf p=\gamma m\mathbf v$}
For a massive particle, its spatial <momentum> in an inertial frame is $\gamma m\mathbf v$, with m its invariant <rest mass> and $\gamma$ the <Lorentz factor>. Together with its <relativistic energy> it forms the <four-momentum>. In a magnetic quadrupole's <paraxial approximation>, replacing $mv$ by the longitudinal momentum extends the transverse focusing scale to relativistic beams.