Searching for new physics with Bs0→K(⁎)0K¯(⁎)0 - A reappraisal

The effective phase 2βseff can be extracted from the indirect CP-violating asymmetry in Bs0→K(⁎)0K¯(⁎)0. In the standard model, 2βseff is expected to vanish, and so its measurement can potentially reveal the presence of new physics. However, there is a theoretical error if the second amplitude, Vub⁎VusPuc′, is non-negligible. Ciuchini, Pierini and Silvestrini (CPS) have suggested measuring Puc in Bd0→K(⁎)0K¯(⁎)0, and relating it to Puc′ using SU(3). For their choice of Cd and Sd, the direct and indirect CP asymmetries in Bd0→K(⁎)0K¯(⁎)0, they find that the error on 2βseff is very small, even allowing for 100% SU(3) breaking. In this Letter, we re-examine the CPS method, allowing for a large range of the Bd,s0→K(⁎)0K¯(⁎)0 observables. We find that, if Cd2+Sd2 is measured to be ≲0.4-0.5, the theoretical error on 2βseff is indeed small, 2-3°. However, for other values of these observables, this error can be quite large, up to 14.9°. This problem can be ameliorated if the values of SU(3) breaking were known, and we discuss different experimental ways of determining this quantity.