Measurements of lifetimes and a limit on the lifetime difference in the neutral D-Meson system

Using the large hadroproduced charm sample collected in experiment E791 at Fermilab, we report the first directly measured constraint on the decay-wid th difference Delta Gamma for the mass eigenstates of the D-0-(D) over bar( 0) system. We obtain our result from lifetime measurements of the decays D- 0 --> K(-)pi(+) and D-0 --> K-K+, under the assumption of CP invariance, wh ich implies that the CP eigenstates and the mass eigenstates are the same. The lifetime of D-0 --> K-K+ (the CP-even final state) is tau(KK) = 0.410 /- 0.011 +/- 0.006 ps, and the lifetime of D-0 --> K(-)pi(+) (an equal mixt ure of CP-odd and CP-even final states) is tau(K pi) = 0.413 +/- 0.003 +/- 0.004 ps. The decay-width difference is Delta Gamma = 2(Gamma(KK) - Gamma(K pi)) = 0.04 +/- 0.14 +/- 0.05 ps(-1). We relate these measurements to meas urements of mixing in the neutral D-meson system.