The $B^+ \to K^+ ν\bar ν$ decay as a search for the QCD axion

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Main Authors: Abumusabh, Merna, Dujany, Giulio, Guadagnoli, Diego, Iohner, Axel, Toni, Claudio
Format: Preprint
Published: 2025
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author Abumusabh, Merna
Dujany, Giulio
Guadagnoli, Diego
Iohner, Axel
Toni, Claudio
author_facet Abumusabh, Merna
Dujany, Giulio
Guadagnoli, Diego
Iohner, Axel
Toni, Claudio
contents We introduce a model-independent framework to reinterpret Belle II results using only public data, analytically reconstructing the mapping between true and reconstructed kinematic variables within the statistically dominant Inclusive Tagging Analysis. This enables rare-decay measurements to probe light invisible particles -- such as the QCD axion or axion-like particles, collectively denoted $a$ -- without relying on internal simulations. Applying the method to $B^+ \! \to \! K^+ ν\barν$ yields the strongest bound on the branching fraction for $B^+ \! \to \! K^+ a$, improving existing limits by about a factor of nine and constraining the axion's fundamental flavour-changing coupling to $b$ and $s$ quarks. The approach establishes $B^+ \! \to \! K^+ ν\barν$ as a dual probe -- simultaneously testing short-distance new physics and light invisible states, the two probes working independently to an excellent approximation -- and provides a general strategy for model-independent reinterpretation of collider data.
format Preprint
id arxiv_https___arxiv_org_abs_2510_18953
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle The $B^+ \to K^+ ν\bar ν$ decay as a search for the QCD axion
Abumusabh, Merna
Dujany, Giulio
Guadagnoli, Diego
Iohner, Axel
Toni, Claudio
High Energy Physics - Phenomenology
High Energy Physics - Experiment
We introduce a model-independent framework to reinterpret Belle II results using only public data, analytically reconstructing the mapping between true and reconstructed kinematic variables within the statistically dominant Inclusive Tagging Analysis. This enables rare-decay measurements to probe light invisible particles -- such as the QCD axion or axion-like particles, collectively denoted $a$ -- without relying on internal simulations. Applying the method to $B^+ \! \to \! K^+ ν\barν$ yields the strongest bound on the branching fraction for $B^+ \! \to \! K^+ a$, improving existing limits by about a factor of nine and constraining the axion's fundamental flavour-changing coupling to $b$ and $s$ quarks. The approach establishes $B^+ \! \to \! K^+ ν\barν$ as a dual probe -- simultaneously testing short-distance new physics and light invisible states, the two probes working independently to an excellent approximation -- and provides a general strategy for model-independent reinterpretation of collider data.
title The $B^+ \to K^+ ν\bar ν$ decay as a search for the QCD axion
topic High Energy Physics - Phenomenology
High Energy Physics - Experiment
url https://arxiv.org/abs/2510.18953