Dilepton asymmetries at B factories in search of ∆ B = − ∆ Q transitions

Bottom meson decay is a promising place to look for CP violation outside the neutral kaon system. It will also facilitate a test of the CP violation mechanism of the standard model [1]. One way to achieve this aim would be to measure decay time asymmetries at the asymmetric B factories presently under construction [2]. But violations of the standard model may show up in B physics in other ways also. Here we focus on the interesting possibility of the breakdown of ∆B = ∆Q rule in semileptonic decays of neutral bottom mesons. This rule is not exact as it is violated in higher order weak interactions. For instance, a ∆B = −∆Q amplitude is generated in the decay B(b̄d) → πeν̄e by two tree-level transitions b̄ → q̄ud̄ and d → qeν̄e by exchanging the quark q = u, c, t. However an estimate of this amplitude may be misleading because we could have additional contributions (at the same order and with the same CKM factors) from the b̄ → d̄ Penguin transition, and the effects due to new particle exchanges in the Penguin loop are unknown [3]. In any case, an experimental check of the ∆B = ∆Q rule as a phenomenological question is important in its own right; the rule forms the basis of lepton-tagging of bottom flavor. For this check, we shall examine the decay time asymmetries involving like-sign dilepton events produced at asymmetric factories of Υ(4S). The parameters of interest are the ratios of semileptonic decay amplitudes for B and B̄ mesons