# Measurement of CP asymmetry in $D^0 \to K^- K^+$ decays

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2017). Measurement of CP asymmetry in $D^0 \to K^- K^+$ decays. Physics Letters B, B767:177-187.

## Abstract

A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay $D^0 \to K^- K^+$ is performed using ppcollision data, corresponding to an integrated luminosity of 3 $fb^{−1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8TeV. The flavour of the charm meson at production is determined from the charge of the pion in $D^{∗+} \to D^0\pi^+ and D^{∗−} \to \overline{D}^0\pi^-$ decays. The time-integrated CP asymmetry $A_{CP}(K^- K^+)$ is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured $D^0 \to K^−\pi^+, D^+ \to K^-\pi^+\pi^+$ and $D^+ \to \overline{K}^0\pi^+$ decays used as calibration channels. It is found to be
$A_{CP}(K^- K^+) = (0.14 \pm 0.15 (stat) \pm 0.10 (syst))$%.
A combination of this result with previous LHCb measurements yields
$A_{CP}(K^- K^+) = (0.04 \pm 0.12 (stat) \pm 0.10 (syst)$)%,
$A_{CP}(\pi^-\pi^+) = (0.07 \pm 0.14 (stat) \pm 0.11 (syst))$%.
These are the most precise measurements from a single experiment. The result for $A_{CP}(K^- K^+)$ is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

## Abstract

A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay $D^0 \to K^- K^+$ is performed using ppcollision data, corresponding to an integrated luminosity of 3 $fb^{−1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8TeV. The flavour of the charm meson at production is determined from the charge of the pion in $D^{∗+} \to D^0\pi^+ and D^{∗−} \to \overline{D}^0\pi^-$ decays. The time-integrated CP asymmetry $A_{CP}(K^- K^+)$ is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured $D^0 \to K^−\pi^+, D^+ \to K^-\pi^+\pi^+$ and $D^+ \to \overline{K}^0\pi^+$ decays used as calibration channels. It is found to be
$A_{CP}(K^- K^+) = (0.14 \pm 0.15 (stat) \pm 0.10 (syst))$%.
A combination of this result with previous LHCb measurements yields
$A_{CP}(K^- K^+) = (0.04 \pm 0.12 (stat) \pm 0.10 (syst)$)%,
$A_{CP}(\pi^-\pi^+) = (0.07 \pm 0.14 (stat) \pm 0.11 (syst))$%.
These are the most precise measurements from a single experiment. The result for $A_{CP}(K^- K^+)$ is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

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