Upper Limits on the DecayD0→μ+μ−and onD0−D¯0Mixing

Abstract

As a by-product to the study of muon pairs produced by 255-Ge V/c pions, data from Fermilab yield upper limits on the decay $D^0\to {\mu }^{+}{\mu }^{-}$ and on $D^0-{\overline{D}}^0$ mixing. An unrestricted sample of 122 630 unlike-sign muon pairs allows a 90%-C.L. (confidence level) upper limit of 1.1×${10}^{-5\mathrm{}}$ to be placed on the branching ratio of the charm-changing neutral-current decay $D^0\to {\mu }^{+}{\mu }^{-}$. From a sample of 3973 like-sign muon pairs, the ratio $r=\frac{\Gamma ({\overline{D}}^0\to {\mu }^{+}X)}{\Gamma ({\overline{D}}^0\to {\mu }^{-}X)}$ is determined to be $r<\mathrm{}5.6\mathrm{}\times {10}^{-3\mathrm{}}$ at 90% C.L.