CP Violation in {B_s}^0 > J psi.phi Decays 87 June 11–15 O.P June 11–15 In publishing this work among the Boston Studies in the Philosophy of Science 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 All measurements are among the most precise available from a single experiment and provide significantly improved constraints on the phenomenology of new particles and interactions