In section 6.1.4 of the Physics Reference Manual it talks about how the angular distribution after multiple scattering is calculated. It introduces a model parameter \mu_0 but doesn't clearly explain what it is. Does \mu_0 represent a hard cutoff for the functions g_1 and g_2, i.e. g_1(u) = C_1 exp(-a*(1-u)) if u >= u_0 *otherwise* 0 g_2(u) = c_2 1/(b-u)**2 if u <= u_0 *otherwise* 0 ?