d d t ⟨ p ( t ) ⟩ = q ( E + ⟨ p ( t ) ⟩ × B m ) − ⟨ p ( t ) ⟩ τ , {\displaystyle {\frac {d}{dt}}\langle \mathbf {p} (t)\rangle =q\left(\mathbf {E} +{\frac {\langle \mathbf {p} (t)\rangle \times \mathbf {B} }{m}}\right)-{\frac {\langle \mathbf {p} (t)\rangle }{\tau }},}