Constraining Extensions of the Quark Sector with the CP Asymmetry in $B\to \psi K_{S}$

TL;DR

This paper investigates how models with extended quark sectors influence the CP asymmetry in B meson decays, providing constraints on new physics parameters using experimental data.

Contribution

It analyzes the effects of extended quark sectors on CP asymmetry in B decays and derives constraints on flavor-changing Z couplings from experimental measurements.

Findings

Significant constraints on the phase of flavor-changing Z couplings.

Extended quark sectors can alter the dominant contributions to B-B̄ mixing.

Implications for CP asymmetry in semileptonic B decays are discussed.

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, $a_{\psi K_{S}} =0.79^{+0.41}_{-0.44}$, 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.