Measurement of the charm mixing parameter $y_{CP}-y_{CP}^{K\ddot{I}€}$ using two-body $D^0$ meson decays

Abstract

A measurement of the ratios of the effective decay widths of $D^0\to \ddot{I}{€}^{-}\ddot{I}{€}^{+}$ and $D^0\to K^{-}{K}^{+}$ decays over that of $D^0\to K^{-}\ddot{I}{€}^{+}$ decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of $13\mathrm{TeV}$, corresponding to an integrated luminosity of $6\mathrm{f}{\mathrm{b}}^{-1}$. These observables give access to the charm mixing parameters $y_{CP}^{\ddot{I}€\ddot{I}€}-y_{CP}^{K\ddot{I}€}$ and $y_{CP}^{KK}-y_{CP}^{K\ddot{I}€}$, and are measured as $y_{CP}^{\ddot{I}€\ddot{I}€}-y_{CP}^{K\ddot{I}€}=(6.57\pm 0.53\pm 0.16)\times 10^{-3}$, $y_{CP}^{KK}-y_{CP}^{K\ddot{I}€}=(7.08\pm 0.30\pm 0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The combination of the two measurements is $y_{CP}-y_{CP}^{K\ddot{I}€}=(6.96\pm 0.26\pm 0.13)\times 10^{-3}$, which is four times more precise than the previous world average.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-041.html (LHCb public pages)