Measurement of the charm-mixing parameter $y_{CP}$ in $D^{0}to K^{0}_{S}omega$ decays at Belle

We report the first measurement of the charm-mixing parameter $y_{CP}$ in $D^{0}$ decays to the $CP$-odd final state $K^{0}_{S}omega$. The study uses the full Belle $e^{+}e^-$ annihilation data sample of $976rm~ fb^{-1}$ taken at or near the $Upsilon(4S)$ centre-of-mass energy. We find $y_{CP} = (0.96 pm 0.91 pm 0.61 {}^{+0.17}_{-0.00})%$, where the first uncertainty is statistical, the second is systematic due to event selection and background, and the last is due to possible presence of $CP$-even decays in the data sample.