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Autores principales: Altmannshofer, Wolfgang, Dror, Jeff A., Giffin, Pierce, Gori, Stefania, Jackson, Ollie, Luong, Khai, Schwendimann, Patrick, Seo, Se Rang
Formato: Preprint
Publicado: 2026
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Acceso en línea:https://arxiv.org/abs/2601.06254
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author Altmannshofer, Wolfgang
Dror, Jeff A.
Giffin, Pierce
Gori, Stefania
Jackson, Ollie
Luong, Khai
Schwendimann, Patrick
Seo, Se Rang
author_facet Altmannshofer, Wolfgang
Dror, Jeff A.
Giffin, Pierce
Gori, Stefania
Jackson, Ollie
Luong, Khai
Schwendimann, Patrick
Seo, Se Rang
contents We study the sensitivity of past and future stopped-pion experiments to light, invisible dark sector particles produced in exotic pion decays. We consider two-body decays involving sterile neutrinos, $π^+ \to \ell^+ N$, as well as three-body decays $π^+ \to \ell^+ ν_\ell X$, with $X$ an invisible scalar, axion-like particle, or dark vector. We recast existing limits from the PIENU experiment and project the reach of the planned PIONEER experiment using detailed simulations based on the current detector design. We find that PIONEER can improve bounds on exotic pion branching ratios by at least one order of magnitude below current limits. We compare the projected sensitivities with complementary constraints from lepton anomalous magnetic moments, mono-photon searches, and beam-dump experiments, identifying weak-violating axion-like particles as a particularly well-motivated benchmark. Our results establish PIONEER as a powerful and complementary probe of light, invisible dark sectors.
format Preprint
id arxiv_https___arxiv_org_abs_2601_06254
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Exploring Invisible New Physics with Exotic Pion Decays
Altmannshofer, Wolfgang
Dror, Jeff A.
Giffin, Pierce
Gori, Stefania
Jackson, Ollie
Luong, Khai
Schwendimann, Patrick
Seo, Se Rang
High Energy Physics - Phenomenology
We study the sensitivity of past and future stopped-pion experiments to light, invisible dark sector particles produced in exotic pion decays. We consider two-body decays involving sterile neutrinos, $π^+ \to \ell^+ N$, as well as three-body decays $π^+ \to \ell^+ ν_\ell X$, with $X$ an invisible scalar, axion-like particle, or dark vector. We recast existing limits from the PIENU experiment and project the reach of the planned PIONEER experiment using detailed simulations based on the current detector design. We find that PIONEER can improve bounds on exotic pion branching ratios by at least one order of magnitude below current limits. We compare the projected sensitivities with complementary constraints from lepton anomalous magnetic moments, mono-photon searches, and beam-dump experiments, identifying weak-violating axion-like particles as a particularly well-motivated benchmark. Our results establish PIONEER as a powerful and complementary probe of light, invisible dark sectors.
title Exploring Invisible New Physics with Exotic Pion Decays
topic High Energy Physics - Phenomenology
url https://arxiv.org/abs/2601.06254