The DO preshower detector consists of scintillator strips with embedded wav
elength-shifting fibers, and a readout using Visible Light Photon Counters.
The response to minimum ionizing particles has been tested with cosmic-ray
muons. We report results on the gain calibration and light-yield distribut
ions. The spatial resolution is investigated taking into account the light
sharing between strips, the effects of multiple scattering and various syst
ematic uncertainties. The detection efficiency and noise contamination are
also investigated. (C) 2001 Elsevier Science B.V. All rights reserved.