Indirect $\boldsymbol{CP}$ Violation in $\boldsymbol{D^0 \rightarrow h^+ h^-}$ Decays at LHCb

TLDR: In this paper, the authors measured the CP asymmetry of the effective lifetime of the meson decaying to a CP eigenstate and showed no evidence of CP violation in the system.

Abstract: Indirect CP violation in the $D^0$ system can be probed by measuring the parameter $A_{\Gamma}$, defined as the CP asymmetry of the effective lifetime of the $D^0$ meson decaying to a CP eigenstate. This can be significantly enhanced beyond Standard Model predictions by new physics. Measurements of $A_{\Gamma}$ using $D^0 \rightarrow K^+K^-$ and $D^0\rightarrow \pi^+\pi^-$ decays reconstructed from pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, are presented. The results are \begin{align*} A_{\Gamma} (\pi\pi) = (+0.33 \pm 1.06 \pm 0.14) \times 10^{-3},\quad A_{\Gamma} (KK) = (-0.35 \pm 0.62 \pm 0.12) \times 10^{-3}, \end{align*} where the uncertainties are statistical and systematic, respectively. These are the most precise measurements of their kind to date, and show no evidence of CP violation.