  An excess in the branching fraction for $B^+ \to K^+ \nu\nu$ recently
measured at Belle II may be a hint of new physics. We perform thorough
likelihood analyses for different new physics scenarios such as $B \to KX$ with
a new invisible particle $X$, or $B\to K\chi\chi$ through a scalar, vector, or
tensor current with $\chi$ being a new invisible particle or a neutrino. We
find that vector-current 3-body decay with $m_X \simeq 0.6$ GeV - which may be
dark matter - is most favored, while 2-body decay with $m_X \simeq 2$ GeV is
also competitive. The best-fit branching fractions for the scalar and tensor
cases are a few times larger than for the 2-body and vector cases. Past BaBar
measurements provide further discrimination, although the best-fit parameters
stay similar.
