Iso-singlet Down Quark Mixing And CP Violation Experiments

We confront the new physics models with extra iso-singlet down quarks in the new CP violation experimental era with $\sin{(2β)}$ and $ε'/ε$ measurements, $K^+ \to π^+ ν\barν$ events, and $x_s$ limits. The closeness of the new experimental results to the standard model theory requires us to include full SM amplitudes in the analysis. In models allowing mixing to a new isosinglet down quark, as in E$_6$, flavor changing neutral currents are induced that allow a $Z^0$ mediated contribution to $B-\bar B$ mixing and which bring in new phases. In $(ρ,η)$, $(x_s,\sin{(γ)})$, and $(x_s, \sin{(2ϕ_s)})$ plots we still find much larger regions in the four down quark model than in the SM, reaching down to $η\approx 0$, $0 \leq \sin{(γ)} \leq 1$, $-.75 \leq \sin{(2α)} \leq 0.15$, and $\sin{(2ϕ_s)}$ down to zero, all at 1$σ$. We elucidate the nature of the cancellation in an order $λ^5$ four down quark mixing matrix element which satisfies the experiments and reduces the number of independent angles and phases. We also evaluate tests of unitarity for the $3\times3$ CKM submatrix.

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