Branching-ratio and CP violation in semi-inclusive flavor-changing top decays

Abstract

Semi-inclusive top decays, $t \to q_i \v$, are examined in the framework of the standard model, with $q_i = u {\rm or} c$, $\v$ : vector meson formed by $q_j \qb_j$ ($q_j = d, s, b$). By using a simple model of hadronization, that is $ 0 \l| \qb_j \gamma^\mu q_j \r| \v = \mv \fv \evj^\mu$, the total branching ratio is expected to be $\br(\tivj) < ({\l| \vij^\ast \vtj \r|}/{\l| \vtb \r|})^2 \times O({10}^{-3})$ depends on the size of the coupling constant $\fv$. On the other hand, the CP asymmetry should be induced only by the long-distance effects of intermediate state $q_k \qb_k$ ($q_k = d, s, b$) that subsequent scatters into the vector meson. The analytical results including the continuum contributions are given with keeping all masses. However, it yields the CP asymmetry to be small, i.e. $\acp (\tivj) < {\im [(\vij^\ast \vtj)^\ast (\vik^\ast \vtk)]}/{\l| \vij^\ast \vtj \r|^2} \times O({10}^{-2})$ for an identified $q_k \qb_k$ intermediate state, and suppressed more again by a factor of $\sim {({m_b}^2 - {m_s}^2)}/{\mv^2}$ for summing up all of them. Particularly, $\acp (t \to u \Upsilon) \simeq \pm 1%$, induced by the intermediate state $d\bar{d}$ or $s\bar{s}$.