Probing new physics in B → D ℓ + ℓ - decays by using angular asymmetries

We present a fully general, model-independent study of a few rare semileptonic B decays that get dominant contributions from W-annihilation and W-exchange diagrams, in particular B0→D¯0ℓ+ℓ-, where ℓ=e,μ. We consider the most general Lagrangian for the decay, and define three angular asymmetries in the Gottfried–Jackson frame, which are sensitive to new physics. We show how these angular asymmetries can easily be extracted from the distribution of events in the Dalitz plot for B→Dℓ+ℓ- decays. Especially a non-zero forward–backward asymmetry within the frame would give the very first hint of possible new physics. These observations are also true for related decay modes, such as B+→D+ℓ+ℓ- and B0→D0ℓ+ℓ-. Moreover, these asymmetry signatures are not affected by either B0–B¯0 or D0–D¯0 mixings. Then this implies that both B0→D¯0ℓ+ℓ- and B0→D0ℓ+ℓ- as well as their CP conjugate modes can all be considered together in our search for signature of new physics. Hence, it would be of great importance to look for and study these decays in the laboratory, LHCb and Belle II in particular.