Study of charm mixing and CP violation with D0 → K±π∓π±π∓ decays

A study of charm mixing and CP violation in D 0 → K ± π ∓ π ± π ∓ 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 fb − 1 . The ratio of promptly produced D 0 → K + π − π + π − to D 0 → K − π + π − π + 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 γ 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 ∆ x and ∆ y , which are nonzero in the presence of CP violation. It is found that $x=\left(0.{85}_{-0.24}^{+0.15}\right)\%$ , $y=\left(0.{21}_{-0.27}^{+0.29}\right)\%$ , ∆ x = (−0 . 02 ± 0 . 04) % and $\Delta y=\left(0.0{2}_{-0.03}^{+0.04}\right)\%$ . These results are consistent with previous measurements and the hypothesis of CP conservation.