Multiple scattering

Repeated deflection of a charged particle through electromagnetic interactions with matter.

For $d\sigma /d\Omega =K/[p^2{\sin }^4(\theta /2)]$ between angular cutoffs, the leading total cross section is $16\pi K/(p^2{\theta }_{\min }^2)$. Multiply its mean count ${\rho }_{n}x\sigma$ by the one-scatter second moment $2{\theta }_{\min }^2\ln ({\theta }_{\max }/{\theta }_{\min })$ to obtain the displayed total angular variance. A single-plane projected variance is half as large. Comparing the scattering angle to a magnetic bend explains the approximately momentum-independent scattering contribution to relative track uncertainty.