Search for $CP$ violation in $D^{+}\to \ddot{I}•\ddot{I}{€}^{+}$ decays

Abstract

A search for charge-parity ($CP$) violation in the Cabibbo-suppressed $D^{+}\to \ddot{I}•\ddot{I}{€}^{+}$ decay is presented, using proton-proton collision data corresponding to an integrated luminosity of $6{\text{ fb}}^{-1}$, collected at a centre-of-mass energy of $13\text{ TeV}$ with the LHCb detector during Run 2. An abundant sample of $D^{+}\to K_{\mathrm{S}}^0\ddot{I}{€}^{+}$ decays is employed to correct for asymmetries arising from the production of the charmed meson and from detection effects associated with the charged pion accompanying the $\ddot{I}•$ meson. Asymmetries induced by interference of multiple processes, such as neutral kaon mixing, regeneration of neutral kaons, and interference between the Cabibbo-favoured $D^{+}\to {\overline{K}}^0\ddot{I}{€}^{+}$ and the doubly Cabibbo-suppressed $D^{+}\to K^0\ddot{I}{€}^{+}$ decay, are subtracted. The direct $CP$ asymmetry in the $D^{+}\to \ddot{I}•\ddot{I}{€}^{+}$ decay is measured to be \begin{equation*} a_{C\!P}(D^+ \to ϕπ^+) = \left(0.1 \pm 4.9\text{ (stat)} \pm 2.4\text{ (syst)} \right)\times 10^{-4}. \end{equation*} For the first time at a hadron collider, the modulus of the ratio and the relative strong phase of the $D^{+}\to K^0\ddot{I}{€}^{+}$ to $D^{+}\to {\overline{K}}^0\ddot{I}{€}^{+}$ decay amplitudes are also investigated. Two-dimensional confidence intervals are reported for these parameters.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/5870/ (LHCb public pages)