The time-dependent angular analysis of Bd → KSll, a new benchmark for new physics

We consider the time-dependent analysis of B-d -> K(S)ll taking into account the time-evolution of the B-d meson and its mixing into (B) over bar (d). We discuss the angular conventions required to define the angular observables in a transparent way with respect to CP conjugation. The inclusion of time evolution allows us to identify six new observables, out of which three could be accessed from a time-dependent tagged analysis. We also show that these observables could be obtained by time-integrated measurements in a hadronic environment if flavour tagging is available. We provide simple and precise predictions for these observables in the SM and in NP models with real contributions to SM and chirally flipped operators, which are independent of form factors and charm-loop contributions. As such, these observables provide robust and powerful cross-checks of the New Physics scenarios currently favoured by global fits to b -> sll data. In addition, we discuss the sensitivity of these observables with respect to NP scenarios involving scalar and tensor operators, or CP-violating phases. We illustrate how these new observables can provide a benchmark to discriminate among the various NP scenarios in b -> s mu mu. We discuss the extension of these results for B-s decays into f(0), eta or eta '.

Automated summary

This study explores the time-dependent analysis of B-d -> K(S)ll, discussing the angular conventions required for defining angular observables and introducing new observables accessible through time-dependent or time-integrated measurements. The predictions for these observables in both the Standard Model and New Physics models provide a robust test for current New Physics scenarios favored by global fits to b -> sll data.