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In light of the recent branching fraction measurement of the B+→K+νν¯ decay by Belle II and its poor agreement with the Standard Model expectation, we analyze the effects of an axionlike particle (ALP) in B meson decays. We assume a long-lived ALP with a mass of the order of the pion mass that decays to two photons. We focus on a scenario where the ALP decay length is of the order of meters such that the ALP has a non-negligible probability to decay outside the detector volume of Belle II, mimicking the B+→K+νν¯ signal. Remarkably, such an arrangement is also relevant for the long-standing B→πK puzzle by noting that the measured B0→π0K0 and B+→π0K+ decays could have a B0→aK0 and B+→aK+ component, respectively. We also argue based on our results that the required ALP-photon effective coupling belongs to a region of parameter space that can be extensively probed in future beam dump experiments like SHiP.
Altmannshofer et al. (Tue,) studied this question.