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Searches for CP violation in two-body charm decays
TL;DR: In this paper, a measurement of the direct CP asymmetry in D^0 \rightarrow K_S^0 K^0 decays is presented and is found to be ======¯¯$A_{CP}(D^0 ) = (-2.9 \pm 5.2 \pm 2.2 ), where the first uncertainty is statistical and the second systematic.
Abstract: The LHCb experiment recorded data corresponding to an integrated luminosity of 3.0 $fb^{-1}$ during its first run of data taking. These data yield the largest samples of charmed hadrons in the world and are used to search for CP violation in the $D^0$ system. Among the many measurements performed at LHCb, a measurement of the direct CP asymmetry in $D^0 \rightarrow K_S^0 K_S^0$ decays is presented and is found to be
$A_{CP}(D^0 \rightarrow K_S^0 K_S^0) = (-2.9 \pm 5.2 \pm 2.2)\, \%, $ where the first uncertainty is statistical and the second systematic. This represents a significant improvement in precision over the previous measurement of this parameter. Measurements of the parameter $A^\Gamma$, defined as the CP asymmetry of the $D^0$ effective lifetime when decaying to a CP eigenstate, are also presented. Using semi-leptonic b-hadron decays to tag the flavour of the $D^0$ meson at production with the $K^+K^-$ and $\pi^+\pi^-$ final states yields $A^\Gamma(K^+K^-) = (-0.134 \pm 0.077^{+0.026}_{-0.034})\, \%,$ $A^\Gamma(\pi^+\pi^-) = (-0.092 \pm 0.145^{+0.025}_{-0.033})\, \%. $
Thus no evidence of direct or indirect CP violation in the $D^0$ system is found, though it is tightly constrained.
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