Study of charm mixing and CP violation with $D^0\to K^{\pm }\ddot{I}{€}^{\mp }\ddot{I}{€}^{\pm }\ddot{I}{€}^{\mp }$ decays

Abstract

A study of charm mixing and CP violation in $D^0\to K^{\pm }\ddot{I}{€}^{\mp }\ddot{I}{€}^{\pm }\ddot{I}{€}^{\mp }$ decays is performed using data collected by the LHCb experiment in proton-proton collisions from 2015 to 2018, corresponding to an integrated luminosity of 6${\text{fb}}^{-1}$. The ratio of promptly produced $D^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ to $D^0\to K^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ decay rates is measured as a function of $D^0$ decay time, both inclusive over phase space and in bins of phase space. Taking external inputs for the $D^0-{\overline{D}}^0$ mixing parameters $x$ and $y$ allows constraints to be obtained on the hadronic parameters of the charm decay. When combined with previous measurements from charm-threshold experiments and at LHCb, improved knowledge is obtained for these parameters, which is valuable for studies of the angle ${\hat{I}}^3$ of the Unitarity Triangle. An alternative analysis is also performed, in which external inputs are taken for the hadronic parameters, and the mixing parameters are determined, including $\hat{I}”x$ and $\hat{I}”y$, which are nonzero in the presence of CP violation. It is found that $x=\left(0.85_{-0.24}^{+0.15}\right)\%$, $y=\left(0.21^{+0.29}-0.27\right)\%$, $\hat{I}”x=\left(-0.02\pm 0.04\right)\%$ and $\hat{I}”y=\left(0.02_{-0.03}^{+0.04}\right)\%$. These results are consistent with previous measurements and the hypothesis of CP conservation.

All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1720 (LHCb public pages)