/ Experiment-HEP arXiv:1111.5023

Measurement of CP--violating asymmetries in $D^0\to\pi^+\pi^-$ and $D^0\to K^+K^-$ decays at CDF

Pages: 29

Abstract: We report on a measurement of CP--violating asymmetries (Acp) in the Cabibbo-suppressed \mbox{$D^0\to\pi^+\pi^-$} and \mbox{$D^0\to K^+K^-$} decays reconstructed in a data sample corresponding to $5.9$~fb$^{-1}$ of integrated luminosity collected by the upgraded Collider Detector at Fermilab. We use the strong decay $D^{*+}\to D^0\pi^+$ to identify the flavor of the charmed meson at production and exploit CP--conserving strong $c\bar{c}$ pair-production in $p\bar{p}$ collisions. High-statistics samples of Cabibbo-favored $D^0\to K^-\pi^+$ decays with and without a $D^{*\pm}$ tag are used to correct for instrumental effects and significantly reduce systematic uncertainties. We measure Acp$(D^0\to\pi^+\pi^-) = \bigl(+0.22\pm0.24(\mbox{stat})\pm0.11(\mbox{syst})\bigr)\%$ and Acp$(D^0\to K^+K^-) = \bigl(-0.24\pm0.22(\mbox{stat})\pm0.09\mbox{(syst)}\bigr)\%$}, in agreement with CP conservation. These are the most precise determinations from a single experiment to date. Under the assumption of negligible direct \CP\ violation in \mbox{$D^0\to\pi^+\pi^-$} and \mbox{$D^0\to K^+K^-$} decays, the results provide an upper limit to the \CP--violating asymmetry in $D^0$ mixing, $|\Acp^{\rm{ind}}(D^0)|< 0.13\%$ %$|\acp{ind}|< 0.13\%$ at the 90\% confidence level.

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