CP Asymmetry A_{\psi K_S}, \sin 2\beta, the Sign of \Delta M_B and the Physics Beyond the Standard Model

Abstract

We demonstrate that the sign of the B^0-\bar B^0 mass difference \Delta M_B is irrelevant for the extraction of the angle \beta=\phi_1 of the unitarity triangle from the CP asymmetry A_{\psi K_S}. Only the weak phase in the mixing amplitude M_{12} matters. Consequently the extraction of \sin 2\beta done by BaBar and Belle can only be affected by new weak phases in M_{12} in the extensions of the SM and possibly but unlikely by new physics contributions to the decay amplitude.