SEARCH FOR D-0(D)OVER-BAR(0) MIXING IN SEMILEPTONIC DECAY MODES

We report the result of a search for D-0 (D) over bar(0) mixing in the data from hadroproduction experiment E791 at Fermilab. We use the cha rge of the pion from the strong decay D-+ --> D-0 pi(+) (and charge c onjugate) to identify the charm quantum number of the neutral D at pro duction, and the charge of the lepton and the kaon in the semileptonic decays D-0 --> Ke nu and K mu nu to identify the charm at the time of decay. No evidence of mixing is seen. We set a 90% confidence level u pper limit on mixing of r < 0.50%, where r = Gamma(D-0 --> (D) over ba r(0) --> K(+)l(-)<(nu)over bar>(l))/(D-0 --> K(-)l(+)nu(l)).