Search for $B^{+} to K^{+} u bar u$ decays with an inclusive tagging method at the Belle II experiment

This contribution illustrates a new search for the flavor-changing neutral-current decay ${B^+ to K^+ u bar u}$ performed by the Belle II experiment at the SuperKEKB asymmetric-energy electron-positron collider. In this study, a sample corresponding to an integrated luminosity of $63, rm{fb}^{-1}$ collected at the $rm Upsilon(4S)$ resonance and an additional sample of $9, rm{fb}^{-1}$ collected at an energy $60, rm MeV$ below the resonance are used. A novel technique, based on an inclusive tagging method and exploiting the topological features of the ${B^+ to K^+ u bar u}$ decay, is employed and it provides a higher signal efficiency with respect to the methods used in the previous searches. No significant signal is observed. An upper limit of $4.1 times 10^{-5}$ is set on the ${B^+ to K^+ u bar u}$ branching fraction at the $90, %$ confidence level.