New FOCUS results on charm mixing and CP violation

TL;DR

This paper reports recent high-statistics measurements of charm meson mixing and CP violation, including lifetime differences, asymmetries, and branching ratios, using data from the FOCUS experiment at Fermilab.

Contribution

It provides new measurements of charm mixing parameters and CP violation asymmetries, with a focus on lifetime differences and decay rate ratios, using a large photoproduction dataset.

Findings

Measured the $y_{CP}$ mixing parameter in the $D^0$ system.

Verified negligible CP violation in certain charm decays.

Reported preliminary branching ratio results for $D^{*+}$ decays.

Abstract

We present a summary of recent results on CP violation and mixing in the charm quark sector based on a high statistics sample collected by photoproduction experiment FOCUS (E831 at Fermilab). We have measured the difference in lifetimes for the $D^0$ decays: $D^0 \to K^-\pi^+$ and $D^0 \to K^-K^+$. This translates into a measurement of the $y_{CP}$ mixing parameter in the $\d0d0$ system, under the assumptions that $K^-K^+$ is an equal mixture of CP odd and CP even eigenstates, and CP violation is negligible in the neutral charm meson system. We verified the latter assumption by searching for a CP violating asymmetry in the Cabibbo suppressed decay modes $D^+ \to K^-K^+\pi^+$, $D^0 \to K^-K^+$ and $D^0 \to \pi^-\pi^+$. We show preliminary results on a measurement of the branching ratio $\Gamma(D^{*+}\to \pi^+ (K^+\pi^-))/\Gamma(D^{*+}\to \pi^+ (K^-\pi^+))$.