Constraining extensions of the quark sector with the CP asymmetry in B ->psi K-S

Models with extended quark sector affect the CP asymmetry in the B --> psi K-S decay, a psi K-s, in two ways: First, the top-mediated box diagram is n ot necessarily the only important contribution to B - (B) over bar mixing. Second, the 3 x 3 CKM matrix is no longer unitary. We analyze the constrain ts that follow from the CDF measurement, a psi K-S = 0.79(-0.44)(+0.41), on the mixing parameters of extended quark sectors. Most noticeably, we find significant constraints on the phase of the relevant flavor changing Z coup ling in models with extra down quarks in vector-like representations. Furth er implications for the CP asymmetry in semileptonic B decays are discussed .