First observation of $D^0-{\bar{D}}^0$ oscillations in $D^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ decays and measurement of the associated coherence parameters

Abstract

Charm meson oscillations are observed in a time-dependent analysis of the ratio of $D^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ to $D^0\to K^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ decay rates, using data corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes $r_D^{K3\ddot{I}€}$ and the product of the coherence factor $R_D^{K3\ddot{I}€}$ and a charm mixing parameter $y_{K3\ddot{I}€}^{{}^{\prime }}$. The constraints measured are $r_D^{K3\ddot{I}€}=(5.67\pm 0.12)\times 10^{-2}$, which is the most precise determination to date, and $R_D^{K3\ddot{I}€}\cdot y_{K3\ddot{I}€}^{{}^{\prime }}=(0.3\pm 1.8)\times 10^{-3}$, which provides useful input for determinations of the CP-violating phase ${\hat{I}}^3$ in $B^{\pm }\to D{K}^{\pm },D\to K^{\mp }\ddot{I}{€}^{\pm }\ddot{I}{€}^{\mp }\ddot{I}{€}^{\pm }$ decays. The analysis also gives the most precise measurement of the $D^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ branching fraction, and the first observation of $D^0-{\bar{D}}^0$ oscillations in this decay mode, with a significance of 8.2 standard deviations.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-057.html