## Saturday, December 3, 2011

### CDF on Charm CP

Thanks to Resonaances for a report on the new CDF paper about $D^0$ decays and the (CP) asymmetry recently measured at LHCb. From the abstract:
We report on a measurement of CP violating asymmetries (Acp) in the Cabibbo suppressed $D^0$ $\rightarrow$ $\pi^{+} \pi^{+}$ and $D^0$ $\rightarrow$ $K^{+} K^{-}$ decays ... We measure Acp($\pi^{+} \pi^{-}$) = $+0.22 \pm 0.24$ (stat) $\pm 0.11$ (syst) (percent) and Acp($K^{+} K^{-}$) = $-0.24 \pm 0.22$ (stat) $\pm 0.09$ (syst), in agreement with CP conservation ... Under the assumption of negligible direct CP violation in both decays, the results provide an upper limit to the CP violating asymmetry in $D^0$ mixing, $|\textrm{Acp}^{\textrm{ind}}| < 0.13$, at the 90 percent confidence level.

1. This appears to rule out the large $-0.82$ result from LHCb, unless the true CDF value sits at the upper end of its error range, and/or some of their assumptions are incorrect.
2. The relevant (EW scale) triality phase is here. The full $4$ parameter mixing of course reduces the phases to the standard small values.