Branching ratios and CP asymmetries of the quasi-two-body decays B_c → K^*_0(1430,1950) D_(s)→ K π D_(s) in the PQCD approach

In this paper, we investigate the quasi-two-body decays B_c → K_0^*(1430,1950) D_(s)→ K π D_(s) within the perterbative QCD (PQCD) framework. The S-wave two-meson distribution amplitudes (DAs) are introduced to describe the final state interactions of the Kπ pair, which involve the time-like form factors and the Gegenbauer polynomials. In the calculations, we adopt two kinds of parameterization schemes to describe the time-like form factors: One is the relativistic Breit-Wigner (RBW) formula, which is usually more siutable for the narrow resonances, and the other is the LASS line shape proposed by the LASS Collaboration, which includes both the resonant and nonresonant components. We find that the branching ratios and the direct CP violations for the decays B_c → K_0^*(1430) D_(s) obtained from those of the quasi-two-body decays B_c → K_0^*(1430) D_(s)→ K π D_(s) under the narrow width approximation (NWA) can be consistent well with the previous PQCD results calculated in the two-body framework by assuming that K^*_0(1430) being the lowest lying q̅ s state, which is so-called scenario II (SII). We conclude that the LASS parameterization is more siutable to describe the K_0^*(1430) than the RBW formula, and the nonresonant components play an important role in the branching ratios of the decays B_c → K_0^*(1430) D_(s)→ K π D_(s). In view of the large difference between the decay width measurements for the K_0^*(1950) given by BaBar and LASS collaborations, we calculate the branching ratios and the CP violations for the quasi-two-body decays B_c → K_0^*(1950) D_(s)→ K π D_(s) by using two values, Γ_K^*_0(1950)=0.100±0.04 GeV and Γ_K^*_0(1950)=0.201±0.034 GeV, besides the two kinds of parameterizations for the resonance K^*_0(1950).