Search for D0-D0bar Mixing

We report on a search for D0-D0bar mixing made by a study of the `wrong-sign' process D0 -> K+pi-. The data come from an integrated luminosity of e+e- collisions at sqrt{s} of about 10 GeV consisting of 9.0 1/fb recorded with the CLEO-II.V detector. We measure the time-integrated rate of the `wrong-sign' process D0 -> K+pi-, relative to that of the Cabibbo-favored process D0bar -> K+pi-, to be R_ws=(0.34+-0.07+-0.06)%. We study that rate as a function of the decay time of the D0, to distinguish the rate of direct doubly-Cabibbo-suppressed decay from D0-D0bar mixing. The amplitudes that describe D0-D0bar mixing, x' and y', are consistent with zero. The one-dimensional limits, at the 95% C.L., that we determine are (1/2)x'^2<0.05%, and -5.9% < y' < 0.3%. All results are preliminary.