  We describe a complete end-to-end simulation of the response of scintillator
counters to charged particles. The counters were extruded with a titanium
dioxide surface coating and two channels for the embedded wavelength-shifting
fibers which are read out by silicon photomultipliers. The simulation includes
the production and propagation of scintillation and Cerenkov photons, the
response of the silicon photomultipliers, and the generation of the signal
waveforms. Probability lookup tables are used to speed up the simulation of the
photon propagation inside the counters. The simulation was tuned to match
measured data obtained from a test-beam study in the Fermilab Meson Test Beam
Facility using 120 GeV protons. The counters are intended to be used in the
cosmic-ray veto detector for the Mu2e experiment at Fermilab.
