Two schematics of the distribution of accelerated particles at an interplanetary shock for two momenta P₁ and P₂, adapted from Zank et al. (2006). Both schematics illustrate the momentum-dependent scale length of the exponential decay upstream of the shock and the corresponding trapping and escape of particles. The only difference between the schematics is the different escape length scales L_p1 and L_p2. The subpanel shows the intensity of the escaped particles for P₁ and P₂. The dashed curves ahead of the escape boundary indicate a larger diffusion length scale corresponding to solar wind turbulence. See text for details.