Model independent determination of the CKM phase $\gamma$ using input from $D^0-\bar{D}^0$ mixing

Abstract

We present a new, amplitude model-independent method to measure the CP violation parameter $\gamma$ in $B^- \to DK^-$ and related decays. Information on charm interference parameters, usually obtained from charm threshold data, is obtained from charm mixing. By splitting the phase space of the $D$ meson decay into several bins, enough information can be gained to measure $\gamma$ without input from the charm threshold. We demonstrate the feasibility of this approach with a simulation study of $B^- \to DK^-$ with $D \to K^+ \pi^- \pi^+ \pi^-$. We compare the performance of our novel approach to that of a previously proposed binned analysis which uses charm interference parameters obtained from threshold data. While both methods provide useful constraints, the combination of the two by far outperforms either of them applied on their own. Such an analysis would provide a highly competitive measurement of $\gamma$. Our simulation studies indicate, subject to assumptions about data yields and the amplitude structure of $D^0 \to K^+ \pi^- \pi^+ \pi^-$, a statistical uncertainty on $\gamma$ of $\sim 12^{\circ}$ with existing data and $\sim 4^{\circ}$ for the LHCb-upgrade.