Measurement of the lifetime difference in D0 meson decays.

We report a measurement of the D 0 -D 0 mixing parameter y C P using 23.4 fb - 1 of data collected near the Y(4S) resonance with the Belle detector at KEKB. y C P is measured from the lifetime difference of D 0 mesons decaying into the K π + state and the CP-even eigenstate K - K + . We find y C P = (-0.5 ′ 1.0 + 0 . 7 - 0 . 8 ) X 10 - 2 , where the first error is statistical and the second is systematic, corresponding to a 95% confidence interval -0.030 < y C P < 0.020.