Trapping penguins with entangled B mesons

The first direct observation of time-reversal (T) violation in the BB‾ system has been reported by the BaBar Collaboration, employing the method of Bañuls and Bernabéu. Given this, we generalize their analysis of the time-dependent T-violating asymmetry (ATAT) to consider different choices of CP tags for which the dominant amplitudes have the same weak phase. As one application, we find that it is possible to measure departures from the universality of sin⁡(2β)sin⁡(2β) directly. If sin⁡(2β)sin⁡(2β) is universal, as in the Standard Model, the method permits the direct determination of penguin effects in these channels. Our method, although no longer a strict test of T, can yield tests of the sin⁡(2β)sin⁡(2β) universality, or, alternatively, of penguin effects, of much improved precision even with existing data sets.