= Screened Rutherford multiple-scattering scaling
{title2=$\theta_{\mathrm{rms}}^2=32\pi K\rho_nx\ln(\theta_{\max}/\theta_{\min})/p^2$}
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 $\rho_nx\sigma$ 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.
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