The search for new physics in $B\to K{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}$ and $B\to K\nu \bar{\nu }$ using precise lattice QCD form factors

We present HPQCD’s improved scalar, vector and tensor form factors for $B\to K$ semileptonic decays, using the heavy-HISQ formalism for more accurate normalisation of the weak currents. Working with masses close to the physical $b$ on the finest ensemble and including three ensembles with physical light quarks, we cover the full physical $q^2$ range with good precision. Our uncertainties at $q^2=0$ are a factor of three better than earlier work. We compare Standard Model observables using our form factors to experimental measurements for the rare flavour changing neutral current processes $B\to K{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}$ and $B\to K\nu \bar{\nu }$ and discuss the significance of the tensions that arise.