Constraining Extensions of the Quark Sector with the CP Asymmetry in $B\to \psi K_S$

Abstract

Models with extended quark sector affect the CP asymmetry in the $B\to \psi K_S$ decay, $a_{\psi K_S}$, in two ways: First, the top-mediated box diagram is not necessarily the only important contribution to $B-\bar{B}$ mixing. Second, the $3\times 3$ CKM matrix is no longer unitary. We analyze the constraints 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 $Z$ coupling in models with extra down quarks in vector-like representations. Further implications for the CP asymmetry in semileptonic $B$ decays are discussed.

Comments: 12 pages, LaTeX, 3 figures