Constraining new physics with the Fermilab measurement of CP violation in B ->psi K-s

Recently, the CDF Collaboration has reported a measurement of the CP asymme try in the B --> psi K-s decay: a(psi K), = 0.74(-0.44)(+0.44). We analyze the constraints that follow from this measurement on the size and the phase of contributions from new physics to B-B mixing. Defining the relative pha se between the full Mt:! amplitude and the standard model contribution to b e 2 theta(d), we find a new bound: sin2 theta(d) greater than or similar to -0.6 (-0.87) at 1 sigma (95% C.L.). Further implications for the CP asymme try in semileptonic B decays are discussed.