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

Summary

Semi-inclusive top decays, t → q_iX_jj, are examined in the framework of the standard model, with q_i = u or c and X_jj a vector meson formed by q_jq_j (q_j = d, s, b). By using a simple model of hadronization, that is «0|q_jγ^μq_j|X_jj» = mx_jj fx_jj ɛ x_jj^μ, the total branching ratio is expected to be B(t → q_iX_jj) < (|V_ij*V_tj|/|V_tb|)² × O(10^-3) depending on the size of the coupling constant fx_jj. On the other hand, the CP asymmetry should be induced only by the long-distance effects of the intermediate state q_kq_k (q_k = d, s, b) that subsequently 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. A_CP (t → q_iX_jj < Im [(V_ij*V_tj)*(V_ik*V_tk)]/|V_ij*V_tj|² × O(10^-2) for an identified q_k\-q_k intermediate state, and suppressed more again by a factor of ~ (m_b² - m_s²)/mxb_jj² for summing up all of them. Particularly, A_CP (t → u Y) \~- \+-1%, induced by the intermediate state d\-d or s-s.