Measurement of B_s mixing parameters from B_s → J/&psi φ decays at CDF and D∅

<!--HTML-->CP violation in B⁰ and B⁺ decays has already been extensively investigated at the B-factories over the last years, while the corresponding knowlege in the B⁰_s system has been lacking so far. B⁰_s mesons are produced with large cross section at the Tevatron collider. Following the measurement of the B⁰_s to <font style="text-decoration: overline;">B</font>⁰_s oscillation frequency in 2006, the D∅ and CDF experiments have now investigated CP asymmetries in B⁰_s meson decays. We report on the first flavor-tagged analyses from both experiments using B⁰_s decays to J/ψφ. This channel is sensitive not only to the width difference ΔΓ in the B⁰_s system but also to the (CP violating) weak phase β_s.