CP Violation in {B_s}^0 > J psi.phi Decays 87 June 11–15 FACG June 11–15 recent research results and practical insights described specifically for this book The phase difference between transition amplitudes (“mixing phase”) is observable and extremely sensitive to contributions from non standard model particles or interactions that may be very hard to detect otherwise – a fact that makes the precise measurement of the B_s mixing phase one of the most important goals of particle physics This thesis reports on the final measurement of the flavor mixing phase in decays of strange bottom mesons (B_s) into J psi and phi mesons performed in high energy proton antiproton collisions recorded by the Collider Experiment at Fermilab