  We present results of a study of the muon decay in orbit (DIO) contribution
to the signal region of muon - electron conversion. Electrons from DIO are the
dominant source of background for muon - electron conversion experiments
because the endpoint of DIO electrons is the same as the energy of electrons
from elastic muon - electron conversion.
  The probability of DIO contribution to the signal region was considered for a
tracker with Gaussian resolution function and with a realistic resolution
function obtained in the application of pattern recognition and momentum
reconstruction Kalman filter based procedure to GEANT simulated DIO events. It
is found that the existence of non Gaussian tails in the realistic resolution
function does not lead to a significant increase in DIO contribution to the
signal region.
  The probability of DIO contribution to the calorimeter signal was studied in
dependence on the resolution, assuming a Gaussian resolution function of
calorimeter. In this study the geometrical acceptance played an important role,
suppressing DIO contribution of the intermediate range electrons from muon
decay in orbit.
