Analysis of Bd → φKS CP asymmetry in a flavour changing Z′ model

According to the recent experimental data, the time-dependent CP asymmetry SφKS for Bd→φKS decay might still be inconsistent with the standard model (SM) expectations. We try to understand the anomaly with a Z′ model associated with flavour changing neutral currents (FCNCs) at the tree level. We find that (i) if neglecting the contributions from the right-handed flavour changing coupling BR sb and setting ξLL = ξLR = ξ and ξLL = ξ, ξLR = 0, we may obtain 0.01<ξ<0.014, 0.0175<ξ<0.0205, 0.021<ξ<0.0255 and 0.004<ξ<0.008, 0.018<ξ<0.028, 0.042<ξ<0.048 for the Bd→φKS decay, respectively; (ii) if considering the contributions coming from BRsb and setting ξLL = ξRL = ξLR = ξRR = ξ and ξLL = ξRL = ξ, ξLR = ξRR = 0, we can obtain 0.005<ξ<0.075, 0.0085<ξ<0.0105, 0.011<ξ<0.013 and 0.0125<ξ<0.0177, 0.0224<ξ<0.025. These results are consistent with the constraints and the assumptions in some literature. ©2007 Chinese Physical Society and IOP Publishing Ltd.