Open Access

Long-lived axionlike particles from tau decays

Yohei Ema^1,*, Patrick J. Fox ^2,†, Matheus Hostert ^3,‡, Tony Menzo ^4,§, Maxim Pospelov^5,6,∥, Anupam Ray ^7,¶, and Jure Zupan ^4,**

¹CERN, Theory Division, CH-1211 Geneva 23, Switzerland
²Theory Division, Fermilab, Batavia, Illinois 60510, USA
³Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
⁴Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA
⁵School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
⁶William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
⁷Department of Physics, University of California Berkeley, Berkeley, California 94720, USA

^*Contact author: yohei.ema@cern.ch
^†Contact author: pjfox@fnal.gov
^‡Contact author: matheus-hostert@uiowa.edu
^§Contact author: menzoad@mail.uc.edu
^∥Contact author: pospelov@umn.edu
^¶Contact author: anupam.ray@berkeley.edu
^**Contact author: zupanje@ucmail.uc.edu

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Phys. Rev. D 112, 115028 – Published 15 December, 2025

DOI: https://doi.org/10.1103/51gx-m32t

Abstract

Axionlike particles (ALPs) are well-motivated examples of light, weakly coupled particles in theories beyond the Standard Model. In this work, we study long-lived ALPs coupled exclusively to leptons in the mass range between $2 m_{e}$ and $m_{τ} - m_{e}$ . For anarchic flavor structure the leptophilic ALP production in tau decays or from ALP-tau bremsstrahlung is enhanced thanks to derivative couplings of the ALP and can surpass production from electron and muon channels, especially for ALPs heavier than $m_{μ}$ . Using past data from high-energy fixed-target experiments such as CHARM and BEBC we place new constraints on the ALP decay constant $f_{a}$ , reaching scales as high as $O (10^{8}) GeV$ in lepton-flavor-violating channels and $f_{a} \sim O (10^{2}) GeV$ in lepton-flavor-conserving ones. We also present projections for the event-rate sensitivity of current and future detectors to ALPs produced at the Fermilab Main Injector, the CERN SPS, and in the forward direction of the LHC. We show that SHiP will be sensitive to $f_{a}$ values that are over an order of magnitude above the existing constraints.

Physics Subject Headings (PhySH)

Axion-like particles

Article Text

References (144)

J. Beacham et al., Physics beyond colliders at CERN: Beyond the standard model working group report, J. Phys. G 47, 010501 (2020).
M. Battaglieri et al., US cosmic visions: New ideas in dark matter 2017: Community report, in U.S. Cosmic Visions: New Ideas in Dark Matter (Maryland University United States, College Park, MD, 2017).
G. Lanfranchi, M. Pospelov, and P. Schuster, The search for feebly interacting particles, Annu. Rev. Nucl. Part. Sci. 71, 279 (2021).
R. D. Peccei and H. R. Quinn, $C P$ conservation in the presence of instantons, Phys. Rev. Lett. 38, 1440 (1977).
S. Weinberg, A new light boson?, Phys. Rev. Lett. 40, 223 (1978).
F. Wilczek, Problem of strong $P$ and $T$ invariance in the presence of instantons, Phys. Rev. Lett. 40, 279 (1978).
R. Balkin, N. Burger, J. L. Feng, and Y. Shadmi, Flavor at FASER: Discovering light scalars beyond minimal flavor violation, J. High Energy Phys. 04 (2025) 071.
C. Delaunay, T. Kitahara, Y. Soreq, and J. Zupan, Light scalar beyond the Higgs mixing limit, J. High Energy Phys. 10 (2025) 222.
J. Heeck and W. Rodejohann, Lepton flavor violation with displaced vertices, Phys. Lett. B 776, 385 (2018).
S. Navas et al. (Particle Data Group), Review of particle physics, Phys. Rev. D 110, 030001 (2024).
A. Jodidio et al., Search for right-handed currents in muon decay, Phys. Rev. D 34, 1967 (1986); 37, 237(E) (1988).
R. Bayes et al. (TWIST Collaboration), Search for two body muon decay signals, Phys. Rev. D 91, 052020 (2015).
A. Aguilar-Arevalo et al. (PIENU Collaboration), Improved search for two body muon decay $μ^{+} \to e^{+} X_{H}$ , Phys. Rev. D 101, 052014 (2020).
L. Calibbi, D. Redigolo, R. Ziegler, and J. Zupan, Looking forward to lepton-flavor-violating ALPs, J. High Energy Phys. 09 (2021) 173.
W. Altmannshofer, J. A. Dror, and S. Gori, New opportunities for detecting axion-lepton interactions, Phys. Rev. Lett. 130, 241801 (2023).
X.-H. Jiang and C.-T. Lu, Leptophilic axionlike particles at forward detectors, Phys. Rev. D 111, 035035 (2025).
J. F. Donoghue, E. Golowich, and B. R. Holstein, Dynamics of the Standard Model: Second Edition (Cambridge University Press, Cambridge, England, 2022).
E. Izaguirre, T. Lin, and B. Shuve, Searching for axionlike particles in flavor-changing neutral current processes, Phys. Rev. Lett. 118, 111802 (2017).
J. A. Dror, R. Lasenby, and M. Pospelov, New constraints on light vectors coupled to anomalous currents, Phys. Rev. Lett. 119, 141803 (2017).
J. A. Dror, R. Lasenby, and M. Pospelov, Dark forces coupled to nonconserved currents, Phys. Rev. D 96, 075036 (2017).
C. Bierlich et al., A comprehensive guide to the physics and usage of pythia 8.3, SciPost Phys. Codebases 2022, 8 (2022).
P. Skands, S. Carrazza, and J. Rojo, Tuning pythia 8.1: The Monash 2013 tune, Eur. Phys. J. C 74, 3024 (2014).
P. Coloma, E. Fernández-Martínez, M. González-López, J. Hernández-García, and Z. Pavlovic, GeV-scale neutrinos: Interactions with mesons and DUNE sensitivity, Eur. Phys. J. C 81, 78 (2021).
S. Alekhin et al., A facility to search for hidden particles at the CERN SPS: THE SHiP physics case, Rep. Prog. Phys. 79, 124201 (2016).
W. Bai and M. H. Reno, Prompt neutrinos and intrinsic charm at SHiP, J. High Energy Phys. 02 (2019) 077.
R. Maciuła, A. Szczurek, J. Zaremba, and I. Babiarz, Production asymmetry of $ν_{τ}$ neutrinos and ${\bar{ν}}_{τ}$ antineutrinos from a fixed target experiment SHiP, J. High Energy Phys. 01 (2020) 116.
R. Mammen Abraham et al. (FASER Collaboration), Neutrino rate predictions for FASER, Phys. Rev. D 110, 012009 (2024).
S. Aoki et al. (DsTau Collaboration), DsTau: Study of tau neutrino production with 400 GeV protons from the CERN-SPS, J. High Energy Phys. 01 (2020) 033.
C. Ahdida et al. (SHiP Collaboration), Reconstruction of $400 GeV / c$ proton interactions with the SHiP-charm project, Eur. Phys. J. C 84, 562 (2024).
R. Mammen Abraham et al. (FASER Collaboration), First measurement of the muon neutrino interaction cross section and flux as a function of energy at the LHC with FASER, Phys. Rev. Lett. 134, 211801 (2025).
M. Fieg, F. Kling, H. Schulz, and T. Sjöstrand, Tuning pythia for forward physics experiments, Phys. Rev. D 109, 016010 (2024).
J. L. Schubert, B. Döbrich, J. Jerhot, and T. Spadaro, On the impact of heavy meson production spectra on searches for heavy neutral leptons, J. High Energy Phys. 02 (2025) 140.
G. A. Alves et al. (E769 Collaboration), Feynman x and transverse momentum dependence of $D^{\pm}$ and $D^{0}, D^{- 0}$ production in 250-GeV $π$ nucleon interactions, Phys. Rev. Lett. 77, 2392 (1996).
R. Albanese, J. Alt, A. Alexandrov, S. Aoki et al. (SHiP Collaboration), BDF/SHiP at the ECN3 high-intensity beam facility, Technical Report No. CERN-SPSC-2023-033, SPSC-P-369, CERN, Geneva, 2023, https://cds.cern.ch/record/2878604.
V. Hewes et al. (DUNE Collaboration), Deep Underground Neutrino Experiment (DUNE) near detector conceptual design report, Instruments 5, 31 (2021).
P. Coloma, J. López-Pavón, L. Molina-Bueno, and S. Urrea, New physics searches using ProtoDUNE and the CERN SPS accelerator, J. High Energy Phys. 01 (2024) 134.
H. Abreu et al. (FASER Collaboration), Search for dark photons with the FASER detector at the LHC, Phys. Lett. B 848, 138378 (2024).
L. A. Anchordoqui et al. (FPF Working Groups), The forward physics facility at the Large Hadron Collider, arXiv:2503.19010.
B. Batell, J. Berger, and A. Ismail, Probing the Higgs portal at the Fermilab short-baseline neutrino experiments, Phys. Rev. D 100, 115039 (2019).
F. A. Alrahman et al. (ICARUS Collaboration), Search for a hidden sector scalar from kaon decay in the di-muon final state at ICARUS, Phys. Rev. Lett. 134, 151801 (2025).
D. S. Ayres et al. (NOvA Collaboration), The NOvA technical design report, Technical Report No. FERMILAB-DESIGN-2007-01, 2007.
P. Abratenko et al. (MicroBooNE Collaboration), Search for a Higgs portal scalar decaying to electron-positron pairs in the MicroBooNE detector, Phys. Rev. Lett. 127, 151803 (2021).
A. M. Cooper-Sarkar et al. (WA66 Collaboration), Search for heavy neutrino decays in the BEBC beam dump experiment, Phys. Lett. 160B, 207 (1985).
R. Barouki, G. Marocco, and S. Sarkar, Blast from the past II: Constraints on heavy neutral leptons from the BEBC WA66 beam dump experiment, SciPost Phys. 13, 118 (2022).
F. Bergsma et al. (CHARM Collaboration), Search for axion like particle production in 400-GeV proton—copper interactions, Phys. Lett. 157B, 458 (1985).
F. Bergsma et al. (CHARM Collaboration), A search for decays of heavy neutrinos in the mass range 0.5-GeV to 2.8-GeV, Phys. Lett. 166B, 473 (1986).
A. Barr, FASER2 overview, in Presented at the FPF8 Workshop (2025), https://indico.cern.ch/event/1473651/contributions/6284552/attachments/3000335/5287123/FASER2-2025-01-22.pdf.
P. Abratenko et al. (MicroBooNE Collaboration), First measurement of $ν_{e}$ and ${\bar{ν}}_{e}$ charged current single charged pion production differential cross sections on argon using the MicroBooNE detector, Phys. Rev. Lett. 135, 061802 (2025).
P. Coloma, J. Martín-Albo, and S. Urrea, Discovering long-lived particles at DUNE, Phys. Rev. D 109, 035013 (2024).
P. Abratenko et al. (MicroBooNE Collaboration), Search for long-lived heavy neutral leptons and Higgs portal scalars decaying in the MicroBooNE detector, Phys. Rev. D 106, 092006 (2022).
P. Abratenko et al. (MicroBooNE Collaboration), Search for heavy neutral leptons in electron-positron and neutral-pion final states with the MicroBooNE detector, Phys. Rev. Lett. 132, 041801 (2024).
R. Acciarri et al. (ArgoNeuT Collaboration), New constraints on tau-coupled heavy neutral leptons with masses $mN = 280 - 970 MeV$ , Phys. Rev. Lett. 127, 121801 (2021).
R. Acciarri et al. (ArgoNeuT Collaboration), First constraints on heavy QCD axions with a liquid argon time projection chamber using the ArgoNeuT experiment, Phys. Rev. Lett. 130, 221802 (2023).
E. Bertuzzo, A. L. Foguel, G. M. Salla, and R. Z. Funchal, New limits on leptophilic axionlike particles and majorons from ArgoNeuT, Phys. Rev. Lett. 130, 171801 (2023).
B. Russell (DUNE Collaboration), The $2 \times 2$ demonstrator—A demonstrator for the DUNE ND-LAr near detector based on the ArgonCube design, Proc. Sci. TAUP2023 (2024) 221.
K. Wresilo (DUNE Collaboration), Overview and status of the $2 \times 2$ NDLAr demonstrator: A pixel-based LArTPC prototype for the DUNE near detector, Proc. Sci. ICHEP2024 (2025) 176.
E. Cortina Gil et al. (NA62 Collaboration), Search for leptonic decays of dark photons at NA62, Phys. Rev. Lett. 133, 111802 (2024).
E. Cortina Gil et al. (NA62 Collaboration), Search for hadronic decays of feebly-interacting particles at NA62, Eur. Phys. J. C 85, 571 (2025).
J. Jerhot (NA62 Collaboration), Projection of finalized NA62 beam-dump analyses to the full 2021–2026 statistics, Technical Report No. NA62-PUB-2025-01, CERN, Geneva, 2025, https://cds.cern.ch/record/2936260.
J. Blumlein et al., Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment, Z. Phys. C 51, 341 (1991).
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).
Y.-D. Tsai, P. deNiverville, and M. X. Liu, Dark photon and muon $g - 2$ inspired inelastic dark matter models at the high-energy intensity frontier, Phys. Rev. Lett. 126, 181801 (2021).
Y. Kyselov and M. Ovchynnikov, Searches for long-lived dark photons at proton accelerator experiments, Phys. Rev. D 111, 015030 (2025).
M. Ovchynnikov, J.-L. Tastet, O. Mikulenko, and K. Bondarenko, Sensitivities to feebly interacting particles: Public and unified calculations, Phys. Rev. D 108, 075028 (2023).
P. Coloma, P. Hernández, and S. Urrea, New bounds on axion-like particles from MicroBooNE, J. High Energy Phys. 08 (2022) 025.
J. Berger and G. Putnam, Sensitivity to kaon decays to ALPs at fixed target experiments, Phys. Rev. D 110, 055035 (2024).
R. Eichler et al. (SINDRUM Collaboration), Limits for shortlived neutral particles emitted $μ^{+}$ or $π^{+}$ decay, Phys. Lett. B 175, 101 (1986).
Y.-S. Liu, D. McKeen, and G. A. Miller, Electrophobic scalar boson and muonic puzzles, Phys. Rev. Lett. 117, 101801 (2016).
T. Araki, K. Asai, and T. Shimomura, Electron beam dump constraints on light bosons with lepton flavor violating couplings, J. High Energy Phys. 11 (2021) 082.
J. D. Bjorken, R. Essig, P. Schuster, and N. Toro, New fixed-target experiments to search for dark gauge forces, Phys. Rev. D 80, 075018 (2009).
S. Andreas, O. Lebedev, S. Ramos-Sanchez, and A. Ringwald, Constraints on a very light $C P$ -odd Higgs of the NMSSM and other axion-like particles, J. High Energy Phys. 08 (2010) 003.
J. D. Bjorken, S. Ecklund, W. R. Nelson, A. Abashian, C. Church, B. Lu, L. W. Mo, T. A. Nunamaker, and P. Rassmann, Search for neutral metastable penetrating particles produced in the SLAC beam dump, Phys. Rev. D 38 (1988) 3375.
E. M. Riordan et al., A search for short lived axions in an electron beam dump experiment, Phys. Rev. Lett. 59, 755 (1987).
M. Davier and H. Nguyen Ngoc, An unambiguous search for a light Higgs boson, Phys. Lett. B 229, 150 (1989).
J. P. Lees et al. (BABAR Collaboration), Search for a dark leptophilic scalar in $e^{+} e^{-}$ collisions, Phys. Rev. Lett. 125, 181801 (2020).
D. Biswas et al. (Belle Collaboration), Search for a dark leptophilic scalar produced in association with $τ + τ$ - pair in $e^{+} e^{-}$ annihilation at center-of-mass energies near 10.58 GeV, Phys. Rev. D 109, 032002 (2024).
Y. M. Andreev et al. (NA64 Collaboration), Search for pseudoscalar bosons decaying into $e^{+} e^{-}$ pairs in the NA64 experiment at the CERN SPS, Phys. Rev. D 104, L111102 (2021).
P. Carenza and G. Lucente, Supernova bound on axionlike particles coupled with electrons, Phys. Rev. D 104, 103007 (2021); 110, 049901(E) (2024).
D. F. G. Fiorillo, T. Pitik, and E. Vitagliano, Supernova production of axion-like particles coupling to electrons, reloaded, Phys. Rev. D 112, 083008 (2025).
A. Caputo, H.-T. Janka, G. Raffelt, and E. Vitagliano, Low-energy supernovae severely constrain radiative particle decays, Phys. Rev. Lett. 128, 221103 (2022).
A. Eberhart, M. Fedele, F. Kahlhoefer, E. Ravensburg, and R. Ziegler, Leptophilic ALPs in laboratory experiments, arXiv:2504.05873.
S. Gninenko (NA64 Collaboration), NA64 status report 2020, Technical Report No. CERN-SPSC-2020-017, SPSC-SR-273, CERN, Geneva, 2020, https://cds.cern.ch/record/2719646.
D. Banerjee et al. (NA64 Collaboration), Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^{+} e^{-}$ pairs, Phys. Rev. D 101, 071101 (2020).
Y. M. Andreev et al. (NA64 Collaboration), First results in the search for dark sectors at NA64 with the CERN SPS high energy muon beam, Phys. Rev. Lett. 132, 211803 (2024).
J. Jaeckel and M. Spannowsky, Probing MeV to 90 GeV axion-like particles with LEP and LHC, Phys. Lett. B 753, 482 (2016).
J. Alda, G. Levati, P. Paradisi, S. Rigolin, and N. Selimovic, Collider and astrophysical signatures of light scalars with enhanced $τ$ couplings, J. High Energy Phys. 06 (2025) 008.
H. Albrecht et al. (ARGUS Collaboration), A search for lepton flavor violating decays $τ \to e α, τ \to μ α$ , Z. Phys. C 68, 25 (1995).
K. Uno et al. (Belle Collaboration), Search for lepton-flavor-violating tau decays to $ℓ α$ at Belle, J. High Energy Phys. 08 (2025) 155.
I. Adachi et al. (Belle-II Collaboration), Search for lepton-flavor-violating $τ$ decays to a lepton and an invisible boson at Belle II, Phys. Rev. Lett. 130, 181803 (2023).
J. P. Lees et al. (BABAR Collaboration), Limits on tau lepton-flavor violating decays in three charged leptons, Phys. Rev. D 81, 111101 (2010).
K. Hayasaka et al., Search for lepton flavor violating tau decays into three leptons with 719 million produced $τ^{+}$ $τ^{-}$ Pairs, Phys. Lett. B 687, 139 (2010).
G. Aad et al. (ATLAS Collaboration), Probing lepton flavour violation via neutrinoless $τ ⟶ 3 μ$ decays with the ATLAS detector, Eur. Phys. J. C 76, 232 (2016).
A. M. Sirunyan et al. (CMS Collaboration), Search for the lepton flavor violating decay $τ \to 3 μ$ in proton-proton collisions at $\sqrt{s} = 13 TeV$ , J. High Energy Phys. 01 (2021) 163.
R. Aaij et al. (LHCb Collaboration), Search for the lepton flavour violating decay $τ^{- -} \to μ^{- -} μ^{+} μ^{- -}$ , J. High Energy Phys. 02 (2015) 121.
I. Adachi et al. (Belle-II Collaboration), Search for lepton-flavor-violating $τ^{- -} \to μ^{- -} μ^{+} μ^{- -}$ decays at Belle II, J. High Energy Phys. 09 (2024) 062.
M. Davier, A. Hocker, and Z. Zhang, The physics of hadronic tau decays, Rev. Mod. Phys. 78, 1043 (2006).
P. Banerjee, T. Engel, A. Signer, and Y. Ulrich, QED at NNLO with McMule, SciPost Phys. 9, 027 (2020).
G. M. Pruna, A. Signer, and Y. Ulrich, Fully differential NLO predictions for the radiative decay of muons and taus, Phys. Lett. B 772, 452 (2017).
S. E. Derenzo, Measurement of the low-energy end of the mu-plus decay spectrum, Phys. Rev. 181, 1854 (1969).
R. Bilger, K. Foehl, H. Clement, M. Croni, A. Erhardt, R. Meier, J. Patzold, and G. J. Wagner, Search for exotic muon decays, Phys. Lett. B 446, 363 (1999).
M. Bauer, M. Neubert, S. Renner, M. Schnubel, and A. Thamm, Flavor probes of axion-like particles, J. High Energy Phys. 09 (2022) 056.
K. Afanaciev et al. (MEG II Collaboration), New limit on the $μ^{+} \to e + γ$ decay with the MEG II experiment, arXiv:2504.15711.
B. Aubert et al. (BABAR Collaboration), Searches for lepton flavor violation in the decays $τ^{\pm} \to e^{\pm} γ$ and $τ^{\pm} \to μ^{\pm} γ$ , Phys. Rev. Lett. 104, 021802 (2010).
A. Abdesselam et al. (Belle Collaboration), Search for lepton-flavor-violating tau-lepton decays to $ℓ γ$ at Belle, J. High Energy Phys. 10 (2021) 19.
Y. Li and Z. Liu, Supernova constraints on lepton flavor violating ALPs, arXiv:2501.12075.
D. F. G. Fiorillo, T. Pitik, and E. Vitagliano, Energy transfer by feebly interacting particles in supernovae: The trapping regime, Phys. Rev. Lett. 135, 071005 (2025).
Z.-M. Huang and Z. Liu, Low-energy supernova constraints on lepton flavor violating axions, J. High Energy Phys. 10 (2025) 024.
Y. Fei, P. Li, Z. Liu, K.-F. Lyu, and M. Pospelov, $W$ -boson exotic decay into three charged leptons at the LHC, Phys. Rev. D 110, L111302 (2024).
M. Ablikim et al. (BESIII Collaboration), Search for the decay $J / ψ \to γ + invisible$ , Phys. Rev. D 101, 112005 (2020).
M. Ablikim et al. (BESIII Collaboration), Search for diphoton decays of an axionlike particle in radiative $J / ψ$ decays, Phys. Rev. D 110, L031101 (2024).
F. Abudinén et al. (Belle-II Collaboration), Search for axion-like particles produced in $e^{+} e^{-}$ collisions at Belle II, Phys. Rev. Lett. 125, 161806 (2020).
W. Altmannshofer et al. (Belle-II Collaboration), The Belle II physics book, Prog. Theor. Exp. Phys. 2019, 123C01 (2019); 2020, 029201(E) (2020).
Y. M. Andreev et al. (NA64 Collaboration), Constraints on new physics in electron $g - 2$ from a search for invisible decays of a scalar, pseudoscalar, vector, and axial vector, Phys. Rev. Lett. 126, 211802 (2021).
S. N. Gninenko and N. V. Krasnikov (NA64 Collaboration), Leptonic scalar portal: Origin of muon $g - 2$ anomaly and dark matter?, Phys. Rev. D 106, 015003 (2022).
B. Radics, L. Molina-Bueno, L. Fields., H. Sieber, and P. Crivelli, Sensitivity potential to a light flavor-changing scalar boson with DUNE and $NA 64 μ$ , Eur. Phys. J. C 83, 775 (2023).
H. Davoudiasl, R. Marcarelli, and E. T. Neil, Lepton-flavor-violating ALPs at the electron-ion collider: A golden opportunity, J. High Energy Phys. 02 (2023) 071.
B. Batell, H. Davoudiasl, R. Marcarelli, E. T. Neil, and S. Trojanowski, Lepton-flavor-violating ALP signals with TeV-scale muon beams, Phys. Rev. D 110, 075039 (2024).
A. Ponten, H. Sieber, B. B. Oberhauser, P. Crivelli, D. Kirpichnikov, S. N. Gninenko, M. Hösgen, L. M. Bueno, M. Mongillo, and A. Zhevlakov, Probing hidden leptonic scalar portals using the NA64 experiment at CERN, Eur. Phys. J. C 84, 1035 (2024).
D. P. Aguillard et al. (Muon $g - 2$ Collaboration), Measurement of the positive muon anomalous magnetic moment to 127 ppb, Phys. Rev. Lett. 135, 101802 (2025).
R. Aliberti et al., The anomalous magnetic moment of the muon in the standard model: An update, Phys. Rep. 1143, 1 (2025).
S. Borsanyi et al., Leading hadronic contribution to the muon magnetic moment from lattice QCD, Nature (London) 593, 51 (2021).
A. Bazavov et al., Hadronic vacuum polarization for the muon $g - 2$ from lattice QCD: Long-distance and full light-quark connected contribution, Phys. Rev. Lett. 135, 011901 (2025).
D. Djukanovic, G. von Hippel, S. Kuberski, H. B. Meyer, N. Miller, K. Ottnad, J. Parrino, A. Risch, and H. Wittig, The hadronic vacuum polarization contribution to the muon $g - 2$ at long distances, J. High Energy Phys. 04 (2025) 098.
T. Blum et al. (RBC and UKQCD Collaborations), Long-distance window of the hadronic vacuum polarization for the Muon $g - 2$ , Phys. Rev. Lett. 134, 201901 (2025).
R. H. Parker, C. Yu, W. Zhong, B. Estey, and H. Müller, Measurement of the fine-structure constant as a test of the standard model, Science 360, 191 (2018).
L. Morel, Z. Yao, P. Cladé, and S. Guellati-Khélifa, Determination of the fine-structure constant with an accuracy of 81 parts per trillion, Nature (London) 588, 61 (2020).
M. Bauer, M. Neubert, and A. Thamm, Collider probes of axion-like particles, J. High Energy Phys. 12 (2017) 044.
C. Cornella, P. Paradisi, and O. Sumensari, Hunting for ALPs with lepton flavor violation, J. High Energy Phys. 01 (2020) 158.
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).
S. Knapen, K. Langhoff, T. Opferkuch, and D. Redigolo, A robust search for lepton flavour violating axions at Mu3e, J. High Energy Phys. 07 (2025) 243.
S. Knapen, T. Opferkuch, D. Redigolo, and M. Tammaro, Displaced searches for axion-like particles and heavy neutral leptons at Mu3e, J. High Energy Phys. 06 (2025) 189.
M. Achasov et al., STCF conceptual design report (volume 1): Physics & detector, Front. Phys. (Beijing) 19, 14701 (2024).
Y. Ema, P. J. Fox, M. Hostert, T. Menzo, M. Pospelov, A. Ray, and J. Zupan (to be published).
M. Hostert, , Zenodo, 10.5281/zenodo.17667773 (2025).
C. Lourenco and H. K. Wohri, Heavy flavour hadro-production from fixed-target to collider energies, Phys. Rep. 433, 127 (2006).
L. Gladilin, Fragmentation fractions of $c$ and $b$ quarks into charmed hadrons at LEP, Eur. Phys. J. C 75, 19 (2015).
M. Cacciari, M. Greco, and P. Nason, The $p_{T}$ spectrum in heavy-flavour hadroproduction., J. High Energy Phys. 05 (1998) 007.
M. Cacciari, S. Frixione, and P. Nason, The $p_{T}$ spectrum in heavy flavor photoproduction, J. High Energy Phys. 03 (2001) 006.
A. Buckley, J. Ferrando, S. Lloyd, K. Nordström, B. Page, M. Rüfenacht, M. Schönherr, and G. Watt, lhapdf6: Parton density access in the LHC precision era, Eur. Phys. J. C 75, 132 (2015).
R. D. Ball et al. (NNPDF Collaboration), The path to proton structure at 1% accuracy, Eur. Phys. J. C 82, 428 (2022).
W. Bai, M. Diwan, M. V. Garzelli, Y. S. Jeong, and M. H. Reno, Far-forward neutrinos at the Large Hadron Collider, J. High Energy Phys. 06 (2020) 032.
W. Bai, M. Diwan, M. V. Garzelli, Y. S. Jeong, K. Kumar, and M. H. Reno, Forward production of prompt neutrinos from charm in the atmosphere and at high energy colliders, J. High Energy Phys. 10 (2023) 142.
A. Bhattacharya, F. Kling, I. Sarcevic, and A. M. Stasto, Forward neutrinos from charm at the Large Hadron Collider, Phys. Rev. D 109, 014040 (2024).
L. Buonocore, F. Kling, L. Rottoli, and J. Sominka, Predictions for neutrinos and new physics from forward heavy hadron production at the LHC, Eur. Phys. J. C 84, 363 (2024).

Phys. Rev. D 112, 115028– Published 15 December, 2025

Vol. 112, Iss. 11 — 1 December 2025

Received 12 August 2025
Accepted 17 November 2025

DOI: https://doi.org/10.1103/51gx-m32t

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.

Published by the American Physical Society

Physical Review D

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Long-lived axionlike particles from tau decays

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