Constraints on invisible B→K X decays

Applying the public \(B^+\to K^+\nu\bar\nu\) likelihood to constrain a generic invisible particle \(X\) in \(B^+\to K^+X\), including a heavy dark-sector mediator interpretation.

Published as: Constraints on invisible \(B^+\to K^+X\) decays from the Belle II \(B^+\to K^+\nu\bar\nu\) measurement, Phys. Rev. D 114, 032003 (2026).

Reinterpreting the measurement as a search for a dark-sector mediator \(X\): posterior on its mass \(m_X\) and coupling \(\mu_X\), for two assumed decay widths \(\Gamma_X\).

Try your own reinterpretation — a minimal starting point for fitting the model at two fixed widths.