Only run 100 events interactively since it's slow now.
Always do phi fits.
Consolidate.
Loop over samples.
Fix filling phi histograms.
Plot phi, z, dphi, dz for 1v events.
Sample name handling; dz plots.
Do the dphi/dz sampling correctly.
Turn on use_f_dz; form_g_dz.
No svdist2d_cut.