Fast CP violation

Abstract

B flavor tagging will be extensively studied at the asymmetric B factories due to its importance in CP asymmetry measurements. The primary tagging modes are the semileptonic decays of the b (lepton tag), or the hadronic b → c(→ s) decays (kaon tag). We suggest that looking for time dependent CP asymmetries in events where one B is tagged leptonically and the other one is tagged with a kaon could result in an early detection of CP violation. Although in the standard model these asymmetries are expected to be small, 1%, they could be measured with about the same amount of data as in the "gold-plated" decay B_d→ψ K_s. In the presence of physics beyond the standard model, these asymmetries could be as large as 5%, and the first CP violation signal in the B system may show up in these events. We give explicit examples of new physics scenarios where this occurs. [S0556-2821(98)09321-7]