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Probing axionlike particles near the neutral pion mass with KOTO data

Reuven Balkin ¹, Stefania Gori ¹, Dean J. Robinson ^2,3, and Christiane Scherb ^2,3

¹Department of Physics, University of California Santa Cruz and Santa Cruz Institute for Particle Physics, 1156 High Street, Santa Cruz, California 95064, USA
²Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA
³Berkeley Center for Theoretical Physics, Department of Physics, University of California, Berkeley, California 94720, USA

Phys. Rev. D 113, 075034 – Published 22 April, 2026

DOI: https://doi.org/10.1103/hpzj-v6dl

Abstract

We demonstrate that novel limits on prompt axionlike particles (ALPs) in the hard-to-probe mass range near the neutral pion—the so-called pion chimney—may be obtained from recasting $K_{L} \to 3 π^{0} \to 6 γ$ data taken by the J-PARC KOTO experiment, to search for $K_{L} \to 2 π^{0} a \to 6 γ$ . We also explore the power of KOTO $6 γ$ data to probe $K_{L} \to 2 π^{0} a$ for a broader range of ALP masses, incorporating displaced decays.

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References (52)

E. Abouzaid et al. (KTeV Collaboration), Final results from the KTeV experiment on the decay $K_{L} \to π^{0} γ γ$ , Phys. Rev. D 77, 112004 (2008).
S. Gori, G. Perez, and K. Tobioka, KOTO vs. NA62 dark scalar searches, J. High Energy Phys. 08 (2020) 110.
J. K. Ahn et al. (KOTO Collaboration), Search for the $K_{L} \to π^{0} ν \bar{ν}$ and $K_{L} \to π^{0} X^{0}$ decays at the J-PARC KOTO experiment, Phys. Rev. Lett. 122, 021802 (2019).
C. Lin et al. (KOTO Collaboration), Search for the pair production of dark particles $X$ with $K_{L}^{0} \to X X$ , $X \to γ γ$ , Phys. Rev. Lett. 130, 111801 (2023).
E. Abouzaid et al. (KTeV Collaboration), Detailed study of the $K_{L} \to π^{0} π^{0} π^{0}$ dalitz plot, Phys. Rev. D 78, 032009 (2008).
R. Balkin, S. Gori, and C. Scherb, Probing $C P$ and flavor violation in neutral kaon decays with ALPs, J. High Energy Phys. 02 (2026) 011.
E. Goudzovski et al., New physics searches at kaon and hyperon factories, Rep. Prog. Phys. 86, 016201 (2023).
T. Kitahara, T. Okui, G. Perez, Y. Soreq, and K. Tobioka, New physics implications of recent search for $K_{L} \to π^{0} ν \bar{ν}$ at KOTO, Phys. Rev. Lett. 124, 071801 (2020).
E. Izaguirre, T. Lin, and B. Shuve, Searching for axionlike particles in flavor-changing neutral current processes, Phys. Rev. Lett. 118, 111802 (2017).
M. Freytsis, Z. Ligeti, and J. Thaler, Constraining the axion portal with $B \to K l^{+} l^{-}$ , Phys. Rev. D 81, 034001 (2010).
M. Bauer, M. Neubert, S. Renner, M. Schnubel, and A. Thamm, Flavor probes of axion-like particles, J. High Energy Phys. 09 (2022) 056.
M. Bauer, M. Neubert, S. Renner, M. Schnubel, and A. Thamm, Consistent treatment of axions in the weak chiral lagrangian, Phys. Rev. Lett. 127, 081803 (2021).
M. Bauer, M. Neubert, S. Renner, M. Schnubel, and A. Thamm, The low-energy effective theory of axions and ALPs, J. High Energy Phys. 04 (2021) 063.
M. Chala, G. Guedes, M. Ramos, and J. Santiago, Running in the ALPs, Eur. Phys. J. C 81, 181 (2021).
J. Martin Camalich, M. Pospelov, P. N. H. Vuong, R. Ziegler, and J. Zupan, Quark flavor phenomenology of the QCD axion, Phys. Rev. D 102, 015023 (2020).
K. Choi, S. H. Im, C. B. Park, and S. Yun, Minimal flavor violation with axion-like particles, J. High Energy Phys. 11 (2017) 070.
A. Celis, J. Fuentes-Martín, and H. Serôdio, An invisible axion model with controlled fcncs at tree level, Phys. Lett. B 741, 117 (2015).
Y. H. Ahn, Flavored Peccei-Quinn symmetry, Phys. Rev. D 91, 056005 (2015).
J. L. Feng, T. Moroi, H. Murayama, and E. Schnapka, Third generation familons, $b$ factories, and neutrino cosmology, Phys. Rev. D 57, 5875 (1998).
K. S. Babu and S. M. Barr, Family symmetry, gravity, and the strong $C P$ problem, Phys. Lett. B 300, 367 (1993).
A. Davidson and A. Vozmediano, The horizontal axion alternative: The interplay of vacuum structure and flavor interactions, Nucl. Phys. B248, 647 (1984).
A. Davidson, V. P. Nair, and K. C. Wali, Peccei-Quinn symmetry as flavor symmetry and grand unification, Phys. Rev. D 29, 1504 (1984).
D. B. Reiss, Can the family group be a global symmetry?, Phys. Lett. 115B, 217 (1982).
A. Davidson and K. C. Wali, Minimal flavor unification via multigenerational Peccei-Quinn symmetry, Phys. Rev. Lett. 48, 11 (1982).
Y. Ema, K. Hamaguchi, T. Moroi, and K. Nakayama, Flaxion: A minimal extension to solve puzzles in the standard model, J. High Energy Phys. 01 (2017) 096.
L. Calibbi, F. Goertz, D. Redigolo, R. Ziegler, and J. Zupan, Minimal axion model from flavor, Phys. Rev. D 95, 095009 (2017).
C. Cornella, A. M. Galda, M. Neubert, and D. Wyler, $K^{\pm} \to π^{\pm} a$ at next-to-leading order in chiral perturbation theory and updated bounds on ALP couplings, J. High Energy Phys. 06 (2024) 029.
C. Cornella, P. Paradisi, and O. Sumensari, Hunting for ALPs with lepton flavor violation, J. High Energy Phys. 01 (2020) 158.
F. Björkeroth, E. J. Chun, and S. F. King, Flavourful axion phenomenology, J. High Energy Phys. 08 (2018) 117.
F. Ertas and F. Kahlhoefer, On the interplay between astrophysical and laboratory probes of MeV-scale axion-like particles, J. High Energy Phys. 07 (2020) 050.
M. B. Gavela, R. Houtz, P. Quilez, R. Del Rey, and O. Sumensari, Flavor constraints on electroweak ALP couplings, Eur. Phys. J. C 79, 369 (2019).
Y. Afik, B. Döbrich, J. Jerhot, Y. Soreq, and K. Tobioka, Probing long-lived axions at the KOTO experiment, Phys. Rev. D 108, 055007 (2023).
T. Masuda et al., Long-lived neutral-kaon flux measurement for the KOTO experiment, Prog. Theor. Exp. Phys. 2016, 013C03 (2016).
T. Masuda, Development and experimental study of the KOTO detector system using three $K_{L}$ neutral decay modes, Ph.D. thesis, Kyoto University, 2014.
S. Navas et al. (Particle Data Group), Review of particle physics, Phys. Rev. D 110, 030001 (2024).
W. Voigt, Über das Gesetz der Intensitätsverteilung innerhalb der Linien eines Gasspektrums, Sitzungsberichte, (München, 1912), Vol. 1912, p. 25, https://publikationen.badw.de/de/003395768.
R. A. Kycia and S. Jadach, Relativistic Voigt profile for unstable particles in high energy physics, J. Math. Anal. Appl. 463, 1040 (2018).
K. Burnham and D. Anderson, Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach (Springer Verlag, Berlin, 2002).
H. Chernoff, On the distribution of the likelihood ratio, Ann. Math. Stat. 25, 573 (1954).
E. Cortina Gil et al. (NA62 Collaboration), Measurement of the very rare $K^{+} \to π^{+} ν \bar{ν}$ decay, J. High Energy Phys. 06 (2021) 093.
E. Cortina Gil et al. (NA62 Collaboration), Measurement of the $K \to π^{+} γ γ$ decay, Phys. Lett. B 850, 138513 (2024).
A. Lai et al. (NA48 Collaboration), Precise measurement of the decay $K_{L} \to π^{0} γ γ$ , Phys. Lett. B 536, 229 (2002).
R. Ogata et al. (E391a Collaboration), Study of the $K_{L}^{0} \to π^{0} π^{0} ν \bar{ν}$ decay, Phys. Rev. D 84, 052009 (2011).
P. del Amo Sanchez et al. (BABAR Collaboration, Search for production of invisible final states in single-photon decays of $ϒ (1 S)$ , Phys. Rev. Lett. 107, 021804 (2011).
A. V. Artamonov et al. (E949 Collaboration), Search for the decay $K^{+} \to π^{+} γ γ$ in the $π^{+}$ momentum region $P > 213 MeV$ /c, Phys. Lett. B 623, 192 (2005).
J. K. Ahn et al. (KOTO Collaboration), Search for the $K_{L} \to π^{0} ν \bar{ν}$ decay at the J-PARC KOTO experiment, Phys. Rev. Lett. 134, 081802 (2025).
A. M. Sirunyan et al. (CMS Collaboration), Measurement of the top quark polarization and $t \bar{t}$ spin correlations using dilepton final states in proton-proton collisions at $\sqrt{s} = 13 TeV$ , Phys. Rev. D 100, 072002 (2019).
Combination of the ATLAS, CMS and LHCb results on the $B_{(s)}^{0} \to μ^{+} μ^{-}$ decays (2020).
R. Mammen Abraham et al. (FASER Collaboration), Shining light on the dark sector: Search for axion-like particles and other new physics in photonic final states with FASER, J. High Energy Phys. 01 (2025) 199.
J. Blumlein et al., Limits on the mass of light (pseudo)scalar particles from Bethe-Heitler $e^{+} e^{-}$ and $μ^{+} μ^{-}$ pair production in a proton—iron beam dump experiment, Int. J. Mod. Phys. A 07, 3835 (1992).
M. Ovchynnikov and A. Zaporozhchenko, Advancing the phenomenology of GeV-scale axionlike particles, Phys. Rev. D 112, 015001 (2025).
J. L. Goity, A. M. Bernstein, and B. R. Holstein, The decay $π^{0} \to γ γ$ to next to leading order in chiral perturbation theory, Phys. Rev. D 66, 076014 (2002).

Phys. Rev. D 113, 075034– Published 22 April, 2026

Vol. 113, Iss. 7 — 1 April 2026

Received 22 August 2025
Accepted 12 March 2026

DOI: https://doi.org/10.1103/hpzj-v6dl

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Probing axionlike particles near the neutral pion mass with KOTO data

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