Constraints on invisible $B^{+}\to K^{+}X$ decays from the Belle II $B^{+}\to K^{+}\nu \bar{\nu }$ measurement

Lorenz Gärtner, Nikolai Krug, Thomas Kuhr +3

The Belle II measurement of the branching fraction for $B^{+}\to K^{+}\nu \bar{\nu }$ shows a $2.7\sigma$ excess over the Standard Model prediction and motivates new-physics explanations such as ax…