In this letter we revisit the Standard Model predictions for Br(B→K(∗)νν) and discuss the opportunities that open up when combining its partial decay rate with that of B→K(∗)ℓℓ. In the Standard Model a suitable ratio of these two modes can be used to extract Ceff9, which is essential for a reliable phenomenological analysis of the B→K(∗)ℓℓ angular observables. The same ratio also proves to be more sensitive to the presence of New Physics in many plausible extensions of the Standard Model. We also suggest that the separate measurement of Br(B→Kνν¯) for high and for low q2's can be helpful for testing the assumed shape of the vector form factor, because the lattice QCD data are obtained at high q2's, whereas the low q2 region is obtained through an extrapolation.
Jan 18, 2023