On Charmless $B\to K_h\eta^{(')}$ Decays with $K_h=K,K^*,K_0^*(1430),K_2^*(1430)$

Abstract

We study the charmless decays $B\to K_h\eta$ and $B\to K_h\eta'$ within the framework of QCD factorization (QCDF) for $K_h= K,K^*,K_0^*(1430)$ and naive factorization for $K_h=K_2^*(1430)$. There are three distinct types of penguin contributions: (i) $b\to sq\bar q\to s\eta_{q}$, (ii) $b\to ss\bar s\to s\eta_s$, and (iii) $b\to s q\bar q\to q \bar K_h$, where $\eta_q=(u\bar u+d\bar d)/\sqrt{2}$ and $\eta_s=s\bar s$. $B\to K^{(*)}\eta^{(')}$ decays are dominated by type-II and type-III penguin contributions. The interference, constructive for $K\eta'$ and $K^*\eta$ and destructive for $K\eta$ and $K^*\eta'$, between type-II and type-III diagrams explains the pattern of $\Gamma(B\to K\eta')\gg\Gamma(B\to K\eta)$ and $\Gamma(B\to K^*\eta')\ll\Gamma(B\to K^*\eta)$. Within QCDF, the observed large rate of the $K\eta'$ mode can be naturally explained without invoking flavor-singlet contributions or something exotic. The decay pattern for $B\to K_0^*(1430)\eta^{(')}$ decays depends on whether the scalar meson $K_0^*(1430)$ is an excited state of $\kappa$ or a lowest-lying $P$-wave $q\bar q$ state. Hence, the experimental measurements of $B\to K_0^*(1430)\eta^{(')}$ can be used to explore the quark structure of $K_0^*(1430)$. If $K_0^*(1430)$ is a low-lying $q\bar q$ bound state, we find that $K_0^*\eta$ has a rate slightly larger than $K_0^*\eta'$ owing to the fact that the $\eta$-$\eta'$ mixing angle in the $\eta_q,\eta_s$ flavor basis is less than $45^\circ$, in agreement with experiment. Type-III penguin diagram does not contribute to $B\to K_2^*\eta^{(')}$ under the factorization hypothesis and type-II diagram dominates.