- Physical Review Journals
All JournalsPhysics Magazine

Physical Review D

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Dark vector boson bremsstrahlung: New form factors for a broader class of models

F. Kling1,2,*, P. Reimitz3,4,†, and A. Ritz4,‡

  • *Contact author: fkling@uci.edu
  • †Contact author: peter@if.usp.br
  • ‡Contact author: aritz@uvic.ca
PDF

Phys. Rev. D 113, 015008 – Published 8 January, 2026

DOI: https://doi.org/10.1103/fxpl-yhc2

Abstract

We explore the sensitivity of collider experiments to a broad class of GeV-scale dark vector models of new physics via production in proton and neutron bremsstrahlung and initial state radiation. This is achieved using a new physically motivated model for timelike vector form factors with generic charges for both protons and neutrons, which is fit to a variety of timelike and spacelike data with quantified uncertainties. The production model for both proton and neutron bremsstrahlung is applied to recast and extend the reach of existing FASER data to GeV-mass dark photons, U(1)B, U(1)B−L, and protophobic vectors, as well as forecasts for millicharged particles at FORMOSA.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (201)

  1. J. L. Feng, Dark matter candidates from particle physics and methods of detection, Annu. Rev. Astron. Astrophys. 48, 495 (2010).
  2. J. Alexander et al., Dark sectors 2016 workshop: Community report, arXiv:1608.08632.
  3. G. Bertone and M. P. Tim Tait, A new era in the search for dark matter, Nature (London) 562, 51 (2018).
  4. G. Arcadi, M. Dutra, P. Ghosh, M. Lindner, Y. Mambrini, M. Pierre, S. Profumo, and F. S. Queiroz, The waning of the WIMP? A review of models, searches, and constraints, Eur. Phys. J. C 78, 203 (2018).
  5. L. Roszkowski, E. M. Sessolo, and S. Trojanowski, WIMP dark matter candidates and searches—current status and future prospects, Rep. Prog. Phys. 81, 066201 (2018).
  6. M. Pospelov, Secluded U(1) below the weak scale, Phys. Rev. D 80, 095002 (2009).
  7. B. Batell, M. Pospelov, and A. Ritz, Probing a secluded U(1) at B-factories, Phys. Rev. D 79, 115008 (2009).
  8. R. Essig, P. Schuster, and N. Toro, Probing dark forces and light hidden sectors at low-energy e+e− colliders, Phys. Rev. D 80, 015003 (2009).
  9. M. Reece and L.-T. Wang, Searching for the light dark gauge boson in GeV-scale experiments, J. High Energy Phys. 07 (2009) 051.
  10. M. Freytsis, G. Ovanesyan, and J. Thaler, Dark force detection in low energy e-p collisions, J. High Energy Phys. 01 (2010) 111.
  11. B. Batell, M. Pospelov, and A. Ritz, Multi-lepton signatures of a hidden sector in rare B decays, Phys. Rev. D 83, 054005 (2011).
  12. M. Freytsis, Z. Ligeti, and J. Thaler, Constraining the axion portal with B→Kl+l−, Phys. Rev. D 81, 034001 (2010).
  13. R. Essig, P. Schuster, N. Toro, and B. Wojtsekhowski, An electron fixed target experiment to search for a new vector boson A’ decaying to e+e−, J. High Energy Phys. 02 (2011) 009.
  14. R. Essig, R. Harnik, J. Kaplan, and N. Toro, Discovering new light states at neutrino experiments, Phys. Rev. D 82, 113008 (2010).
  15. K. L. McDonald and D. E. Morrissey, Low-energy signals from kinetic mixing with a warped Abelian hidden sector, J. High Energy Phys. 02 (2011) 087.
  16. M. Williams, C. P. Burgess, A. Maharana, and F. Quevedo, New constraints (and motivations) for Abelian gauge bosons in the MeV-TeV mass range, J. High Energy Phys. 08 (2011) 106.
  17. H. Davoudiasl, H.-S. Lee, and W. J. Marciano, ‘Dark’ Z implications for parity violation, rare meson decays, and Higgs physics, Phys. Rev. D 85, 115019 (2012).
  18. Y. Kahn and J. Thaler, Searching for an invisible A’ vector boson with DarkLight, Phys. Rev. D 86, 115012 (2012).
  19. S. Andreas, C. Niebuhr, and A. Ringwald, New limits on hidden photons from past electron beam dumps, Phys. Rev. D 86, 095019 (2012).
  20. 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 (2017), arXiv:1707.04591.
  21. S. Knapen, T. Lin, and K. M. Zurek, Light dark matter: Models and constraints, Phys. Rev. D 96, 115021 (2017).
  22. B. Batell, M. Pospelov, and A. Ritz, Exploring portals to a hidden sector through fixed targets, Phys. Rev. D 80, 095024 (2009).
  23. P. deNiverville, M. Pospelov, and A. Ritz, Observing a light dark matter beam with neutrino experiments, Phys. Rev. D 84, 075020 (2011).
  24. P. deNiverville, D. McKeen, and A. Ritz, Signatures of sub-GeV dark matter beams at neutrino experiments, Phys. Rev. D 86, 035022 (2012).
  25. Y. Kahn, G. Krnjaic, J. Thaler, and M. Toups, DAEδALUS and dark matter detection, Phys. Rev. D 91, 055006 (2015).
  26. C. Adams et al. (LBNE Collaboration), The long-baseline neutrino experiment: Exploring fundamental symmetries of the universe, in Snowmass 2013: Workshop on Energy Frontier (2013), arXiv:1307.7335.
  27. D. E. Soper, M. Spannowsky, C. J. Wallace, and T. M. P. Tait, Scattering of dark particles with light mediators, Phys. Rev. D 90, 115005 (2014).
  28. B. A. Dobrescu and C. Frugiuele, GeV-scale dark matter: Production at the main injector, J. High Energy Phys. 02 (2015) 019.
  29. P. Coloma, B. A. Dobrescu, C. Frugiuele, and R. Harnik, Dark matter beams at LBNF, J. High Energy Phys. 04 (2016) 047.
  30. C. Alpigiani et al. (MATHUSLA Collaboration), A letter of intent for MATHUSLA: A dedicated displaced vertex detector above ATLAS or CMS, arXiv:1811.00927.
  31. A. Ariga et al. (FASER Collaboration), Technical proposal for FASER: Forward search experiment at the LHC, arXiv:1812.09139.
  32. B. Dutta, D. Kim, S. Liao, J.-C. Park, S. Shin, L. E. Strigari, and A. Thompson, Searching for dark matter signals in timing spectra at neutrino experiments, J. High Energy Phys. 01 (2022) 144.
  33. B. Batell, J. L. Feng, and S. Trojanowski, Detecting dark matter with far-forward emulsion and liquid argon detectors at the LHC, Phys. Rev. D 103, 075023 (2021).
  34. B. Batell, J. L. Feng, A. Ismail, F. Kling, R. M. Abraham, and S. Trojanowski, Discovering dark matter at the LHC through its nuclear scattering in far-forward emulsion and liquid argon detectors, Phys. Rev. D 104, 035036 (2021).
  35. 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).
  36. E. Izaguirre, G. Krnjaic, P. Schuster, and N. Toro, New electron beam-dump experiments to search for MeV to few-GeV dark matter, Phys. Rev. D 88, 114015 (2013).
  37. M. D. Diamond and P. Schuster, Searching for light dark matter with the SLAC millicharge experiment, Phys. Rev. Lett. 111, 221803 (2013).
  38. E. Izaguirre, G. Krnjaic, P. Schuster, and N. Toro, Physics motivation for a pilot dark matter search at Jefferson Laboratory, Phys. Rev. D 90, 014052 (2014).
  39. B. Batell, R. Essig, and Z. Surujon, Strong constraints on Sub-GeV dark sectors from SLAC beam dump E137, Phys. Rev. Lett. 113, 171802 (2014).
  40. J. P. Lees et al. (BABAR Collaboration, Search for invisible decays of a dark photon produced in e+e− collisions at BABAR, Phys. Rev. Lett. 119, 131804 (2017).
  41. A. Berlin, P. deNiverville, A. Ritz, P. Schuster, and N. Toro, Sub-GeV dark matter production at fixed-target experiments, Phys. Rev. D 102, 095011 (2020).
  42. G. Krnjaic et al., A snowmass whitepaper: Dark matter production at intensity-frontier experiments, arXiv:2207.00597.
  43. A. Berlin, N. Blinov, G. Krnjaic, P. Schuster, and N. Toro, Dark matter, millicharges, axion and scalar particles, gauge bosons, and other new physics with LDMX, Phys. Rev. D 99, 075001 (2019).
  44. M. Bauer, P. Foldenauer, and J. Jaeckel, Hunting all the hidden photons, J. High Energy Phys. 07 (2018) 094.
  45. A. Berlin, G. Krnjaic, and E. Pinetti, Reviving MeV-GeV indirect detection with inelastic dark matter, Phys. Rev. D 110, 035015 (2024).
  46. C.-T. Lu, J. Tu, and L. Wu, Probing inelastic dark matter at the LHC, FASER, and STCF, Phys. Rev. D 109, 015018 (2024).
  47. M. Mongillo, A. Abdullahi, B. B. Oberhauser, P. Crivelli, M. Hostert, D. Massaro, L. M. Bueno, and S. Pascoli, Constraining light thermal inelastic dark matter with NA64, Eur. Phys. J. C 83, 391 (2023).
  48. A. Filimonova, S. Junius, L. Lopez Honorez, and S. Westhoff, Inelastic Dirac dark matter, J. High Energy Phys. 06 (2022) 048.
  49. M. Carrillo González and N. Toro, Cosmology and signals of light pseudo-Dirac dark matter, J. High Energy Phys. 04 (2022) 060.
  50. B. Batell, J. L. Feng, M. Fieg, A. Ismail, F. Kling, R. M. Abraham, and S. Trojanowski, Hadrophilic dark sectors at the forward physics facility, Phys. Rev. D 105, 075001 (2022).
  51. G. D. V. Garcia, F. Kahlhoefer, M. Ovchynnikov, and T. Schwetz, Not-so-inelastic dark matter, J. High Energy Phys. 02 (2025) 127.
  52. S. Abrahamyan et al. (APEX Collaboration), Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment, Phys. Rev. Lett. 107, 191804 (2011).
  53. F. Archilli et al. (KLOE-2 Collaboration), Search for a vector gauge boson in ϕ meson decays with the KLOE detector, Phys. Lett. B 706, 251 (2012).
  54. J. P. Lees et al. (BABAR Collaboration, Search for low-mass dark-sector Higgs bosons, Phys. Rev. Lett. 108, 211801 (2012).
  55. J. Beacham et al., Physics beyond colliders at CERN: Beyond the standard model working group report, J. Phys. G 47, 010501 (2020).
  56. C. Adams et al. (LBNE Collaboration), The long-baseline neutrino experiment: Exploring fundamental symmetries of the universe, in Snowmass 2013: Workshop on Energy Frontier (2013), arXiv:1307.7335.
  57. A. A. Aguilar-Arevalo et al. (MiniBooNE Collaboration), Dark matter search in a proton beam dump with MiniBooNE, Phys. Rev. Lett. 118, 221803 (2017).
  58. A. A. Aguilar-Arevalo et al. (MiniBooNE DM Collaboration), Dark matter search in nucleon, pion, and electron channels from a proton beam dump with MiniBooNE, Phys. Rev. D 98, 112004 (2018).
  59. C. Alpigiani et al. (MATHUSLA Collaboration), A letter of intent for MATHUSLA: A dedicated displaced vertex detector above ATLAS or CMS, arXiv:1811.00927.
  60. J. P. Lees et al. (BABAR Collaboration), Search for invisible decays of a dark photon produced in e+e− collisions at BABAR, Phys. Rev. Lett. 119, 131804 (2017).
  61. D. Banerjee et al., Dark matter search in missing energy events with NA64, Phys. Rev. Lett. 123, 121801 (2019).
  62. C. Antel et al., Feebly-interacting particles: FIPs 2022 workshop report, Eur. Phys. J. C 83, 1122 (2023).
  63. A. Berlin and F. Kling, Inelastic dark matter at the LHC lifetime frontier: ATLAS, CMS, LHCb, CODEX-b, FASER, and MATHUSLA, Phys. Rev. D 99, 015021 (2019).
  64. J. L. Feng, I. Galon, F. Kling, and S. Trojanowski, Forward search experiment at the LHC, Phys. Rev. D 97, 035001 (2018).
  65. M. Anelli et al. (SHiP Collaboration), A facility to search for hidden particles (SHiP) at the CERN SPS, arXiv:1504.04956.
  66. P. A. Machado, O. Palamara, and D. W. Schmitz, The short-baseline neutrino program at Fermilab, Annu. Rev. Nucl. Part. Sci. 69, 363 (2019).
  67. B. Abi et al. (DUNE Collaboration), Prospects for beyond the standard model physics searches at the deep underground neutrino experiment, Eur. Phys. J. C 81, 322 (2021).
  68. A. Celentano, L. Darmé, L. Marsicano, and E. Nardi, New production channels for light dark matter in hadronic showers, Phys. Rev. D 102, 075026 (2020).
  69. F. Capozzi, B. Dutta, G. Gurung, W. Jang, I. M. Shoemaker, A. Thompson, and J. Yu, Extending the reach of leptophilic boson searches at DUNE and MiniBooNE with bremsstrahlung and resonant production, Phys. Rev. D 104, 115010 (2021).
  70. N. Blinov, P. J. Fox, K. J. Kelly, P. A. N. Machado, and R. Plestid, Dark fluxes from electromagnetic cascades, J. High Energy Phys. 07 (2024) 022.
  71. P. Lo Chiatto and F. Yu, Consistent electroweak phenomenology of a nearly degenerate Z’ boson, Phys. Rev. D 111, 035001 (2025).
  72. W. Altmannshofer, J. A. Dror, and S. Gori, New opportunities for detecting axion-lepton interactions, Phys. Rev. Lett. 130, 241801 (2023).
  73. D. Curtin, Y. Kahn, and R. Nguyen, Dark photons from charged pion bremsstrahlung at proton beam experiments, Phys. Rev. D 108, 095039 (2023).
  74. Y. Kyselov and M. Ovchynnikov, Searches for long-lived dark photons at proton accelerator experiments, Phys. Rev. D 111, 015030 (2025).
  75. L. A. Anchordoqui et al., The forward physics facility: Sites, experiments, and physics potential, Phys. Rep. 968, 1 (2022).
  76. J. L. Feng et al., The forward physics facility at the high-luminosity LHC, J. Phys. G 50, 030501 (2023).
  77. J. Adhikary et al., Scientific program for the forward physics facility, Eur. Phys. J. C 85, 430 (2025).
  78. J. Blümlein and J. Brunner, New exclusion limits on dark gauge forces from proton bremsstrahlung in beam-dump data, Phys. Lett. B 731, 320 (2014).
  79. P. deNiverville, C.-Y. Chen, M. Pospelov, and A. Ritz, Light dark matter in neutrino beams: Production modelling and scattering signatures at MiniBooNE, T2K and SHiP, Phys. Rev. D 95, 035006 (2017).
  80. S. Foroughi-Abari and A. Ritz, Dark sector production via proton bremsstrahlung, Phys. Rev. D 105, 095045 (2022).
  81. S. Foroughi-Abari, P. Reimitz, and A. Ritz, A closer look at dark vector splitting functions in proton bremsstrahlung, Phys. Rev. D 112, 015030 (2025).
  82. D. Gorbunov and E. Kriukova, Pauli form factor contributions to the inelastic proton bremsstrahlung and dark photon production, J. High Energy Phys. 02 (2025) 018.
  83. D. Gorbunov and E. Kriukova, Dark photon production via inelastic proton bremsstrahlung with Pauli form factor, Phys. Part. Nucl. 56, 506 (2025).
  84. S. Okubo, Phi meson and unitary symmetry model, Phys. Lett. 5, 165 (1963).
  85. G. Zweig, An SU(3) Model for Strong Interaction Symmetry and its Breaking. Version 2 (1964), pp. 22–101, 10.17181/CERN-TH-412.
  86. J. Iizuka, Systematics and phenomenology of meson family, Prog. Theor. Phys. Suppl. 37, 21 (1966).
  87. H. Czyż, J. H. Kühn, and S. Tracz, Nucleon form factors and final state radiative corrections to e+e−→pp¯γ, Phys. Rev. D 90, 114021 (2014).
  88. G. P. Lepage and S. J. Brodsky, Exclusive processes in perturbative quantum chromodynamics, Phys. Rev. D 22, 2157 (1980).
  89. C. Adamuščin, E. Bartoš, S. Dubnička, and A. Z. Dubničková, Numerical values of fF, fD, fS coupling constants in SU(3) invariant interaction Lagrangian of vector-meson nonet with 1/2+ octet baryons, Phys. Rev. C 93, 055208 (2016).
  90. A. Faessler, M. I. Krivoruchenko, and B. V. Martemyanov, Once more on electromagnetic form factors of nucleons in extended vector meson dominance model, Phys. Rev. C 82, 038201 (2010).
  91. M. Ablikim et al. (BESIII Collaboration), Measurement of the proton form factor by studying e+e−→pp¯, Phys. Rev. D 91, 112004 (2015).
  92. A. Antonelli et al., The first measurement of the neutron electromagnetic form-factors in the timelike region, Nucl. Phys. B517, 3 (1998).
  93. B. Delcourt et al., Study of the reaction e+e−→pp¯ in the total energy range 1925-MeV–2180-MeV, Phys. Lett. 86B, 395 (1979).
  94. T. K. Pedlar et al. (CLEO Collaboration), Precision measurements of the timelike electromagnetic form-factors of pion, kaon, and proton, Phys. Rev. Lett. 95, 261803 (2005).
  95. M. Castellano, G. Di Giugno, J. W. Humphrey, E. Sassi Palmieri, G. Troise, U. Troya, and S. Vitale, The reaction e+e−→pp¯ at a total energy of 2.1 gev, Nuovo ento Soc. Ital. Fis. 14A, 1 (1973).
  96. T. A. Armstrong et al. (E760 Collaboration), Measurement of the proton electromagnetic form-factors in the timelike region at 8.9−GeV2–13−GeV2, Phys. Rev. Lett. 70, 1212 (1993).
  97. M. Ambrogiani et al. (E835 Collaboration), Measurements of the magnetic form-factor of the proton in the timelike region at large momentum transfer, Phys. Rev. D 60, 032002 (1999).
  98. M. Andreotti et al., Measurements of the magnetic form factor of the proton for timelike momentum transfers, Phys. Lett. B 559, 20 (2003).
  99. J. P. Lees et al. (BABAR Collaboration, Study of e+e−→pp¯ via initial-state radiation at BABAR, Phys. Rev. D 87, 092005 (2013).
  100. A. J. R. Puckett et al., Final analysis of proton form factor ratio data at Q2=4.0, 4.8 and 5.6  GeV2, Phys. Rev. C 85, 045203 (2012).
  101. A. J. R. Puckett et al., Polarization transfer observables in elastic electron proton scattering at Q2=2.5, 5.2, 6.8, and 8.5  GeV2, Phys. Rev. C 96, 055203 (2017); 98, 019907(E) (2018).
  102. V. Punjabi et al., Proton elastic form-factor ratios to Q2=3.5−GeV2 by polarization transfer, Phys. Rev. C 71, 055202 (2005); 71, 069902(E) (2005).
  103. M. E. Christy et al. (E94110 Collaboration), Measurements of electron proton elastic cross-sections for 0.4<Q2<5.5 (GeV/c)2, Phys. Rev. C 70, 015206 (2004).
  104. J. C. Bernauer, Measurement of the elastic electron-proton cross section and separation of the electric and magnetic form factor in the Q2 range from 0.004 to 1 (GeV/c)2, Ph.D. thesis, Mainz University, Inst. Kernphys., 2010.
  105. M. Ablikim et al. (BESIII Collaboration), Measurement of proton electromagnetic form factors in e+e−→pp¯ in the energy region 2.00–3.08 GeV, Phys. Rev. Lett. 124, 042001 (2020).
  106. G. Hohler, E. Pietarinen, I. Sabba Stefanescu, F. Borkowski, G. G. Simon, V. H. Walther, and R. D. Wendling, Analysis of electromagnetic nucleon form-factors, Nucl. Phys. B114, 505 (1976).
  107. W. Bartel, F. W. Busser, W. Dix, R. Felst, D. Harms, H. Krehbiel, P. E. Kuhlmann, J. McElroy, J. Meyer, and G. Weber, Measurement of proton and neutron electromagnetic form-factors at squared four momentum transfers up to 3−GeV/c2, Nucl. Phys. B58, 429 (1973).
  108. T. Janssens, R. Hofstadter, E. B. Hughes, and M. R. Yearian, Proton form factors from elastic electron-proton scattering, Phys. Rev. 142, 922 (1966).
  109. M. Ablikim et al. (BESIII Collaboration), Measurement of proton electromagnetic form factors in the timelike region using initial state radiation at BESIII, Phys. Lett. B 817, 136328 (2021).
  110. B. Plaster et al. (Jefferson Laboratory E93-038 Collaboration), Measurements of the neutron electric to magnetic form-factor ratio GEn/GMn via the H-2(polarized-e, e-prime, polarized-n)H-1 reaction to Q2=1.45−(GeV/c)2, Phys. Rev. C 73, 025205 (2006).
  111. E. Geis et al. (BLAST Collaboration), The charge form factor of the neutron at low momentum transfer from the H-2-polarized (e-polarized, e-prime n) p reaction, Phys. Rev. Lett. 101, 042501 (2008).
  112. J. Golak, G. Ziemer, H. Kamada, H. Witala, and W. Gloeckle, Extraction of electromagnetic neutron form-factors through inclusive and exclusive polarized electron scattering on polarized He-3 target, Phys. Rev. C 63, 034006 (2001).
  113. D. I. Glazier et al., Measurement of the electric form-factor of the neutron at Q2=0.3−(GeV/c)2 to 0.8−(GeV/c)2, Eur. Phys. J. A 24, 101 (2005).
  114. G. Warren et al. (Jefferson Lab E93-026 Collaboration), Measurement of the electric form-factor of the neutron at Q2=0.5 and 1.0  GeV2/c2, Phys. Rev. Lett. 92, 042301 (2004).
  115. H. Zhu et al. (E93026 Collaboration), A measurement of the electric form-factor of the neutron through polarized-d (polarized-e, e-prime n)p at Q2=0.5−(GeV/c)2, Phys. Rev. Lett. 87, 081801 (2001).
  116. C. Herberg et al., Determination of the neutron electric form-factor in the D(e,e’ n)p reaction and the influence of nuclear binding, Eur. Phys. J. A 5, 131 (1999).
  117. M. Ostrick et al., Measurement of the neutron electric form-factor G(E,n) in the quasifree H-2(e(pol.),e’ n(pol.))p reaction, Phys. Rev. Lett. 83, 276 (1999).
  118. I. Passchier et al., The charge form-factor of the neutron from the reaction polarized H-2(polarized e, e-prime n) p, Phys. Rev. Lett. 82, 4988 (1999).
  119. T. Eden et al., Electric form factor of the neutron from the H2(e→,e′n→)H1 reaction at Q2=0.255 (GeV/c)2, Phys. Rev. C 50, R1749 (1994).
  120. R. W. Berard, F. R. Buskirk, E. B. Dally, J. N. Dyer, X. K. Maruyama, R. L. Topping, and T. J. Traverso, Elastic electron deuteron scattering, Phys. Lett. B 47, 355 (1973).
  121. S. Rock, R. G. Arnold, P. E. Bosted, B. T. Chertok, B. A. Mecking, I. A. Schmidt, Z. M. Szalata, R. York, and R. Zdarko, Measurement of elastic electron—neutron cross-sections up to Q2=10−(GeV/c)2, Phys. Rev. Lett. 49, 1139 (1982).
  122. A. Lung et al., Measurements of the electric and magnetic form-factors of the neutron from Q2=1.75−GeV/c2 to 4−GeV/c2, Phys. Rev. Lett. 70, 718 (1993).
  123. B. Anderson et al. (Jefferson Lab E95-001 Collaboration), Extraction of the neutron magnetic form factor from quasi-elastic He→3(e→,e′) at Q2=0.1–0.6 (GeV/c)2, Phys. Rev. C 75, 034003 (2007).
  124. G. Kubon et al., Precise neutron magnetic form-factors, Phys. Lett. B 524, 26 (2002).
  125. H. Anklin et al., Precise measurements of the neutron magnetic form-factor, Phys. Lett. B 428, 248 (1998).
  126. M. Ablikim et al. (BESIII Collaboration), Oscillating features in the electromagnetic structure of the neutron, Nat. Phys. 17, 1200 (2021).
  127. V. Druzhinin et al., Study of e+e− annihilation into hadrons with the SND detector at the VEPP-2000 collider, Proc. Sci., EPS-HEP2019 (2020) 509.
  128. D. W. Hogg, J. Bovy, and D. Lang, Data analysis recipes: Fitting a model to data, arXiv:1008.4686.
  129. S. Navas et al. (Particle Data Group), Review of particle physics, Phys. Rev. D 110, 030001 (2024).
  130. P. Virtanen et al., scipy 1.0: Fundamenta algorithms for scientific computing in python, Nat. Methods 17, 261 (2020).
  131. F. James and M. Roos, minuit: A system for function minimization and analysis of the parameter errors and correlations, Comput. Phys. Commun. 10, 343 (1975).
  132. H. Dembinski, P. Ongmongkolkul et al., scikit-hep/iminuit, 10.5281/zenodo.3949207.
  133. A. K. Likhoded, A. V. Luchinsky, and A. A. Novoselov, Light hadron production in inclusive pp-scattering at LHC, Phys. Rev. D 82, 114006 (2010).
  134. H. Abreu et al. (FASER Collaboration), The FASER detector, J. Instrum. 19, P05066 (2024).
  135. H. Abreu et al. (FASER Collaboration), Detecting and studying high-energy collider neutrinos with FASER at the LHC, Eur. Phys. J. C 80, 61 (2020).
  136. H. Abreu et al. (FASER Collaboration), Technical proposal: FASERnu, arXiv:2001.03073.
  137. R. Mammen Abraham et al. (FASER Collaboration), Reconstruction and performance evaluation of FASER’s emulsion detector at the LHC, J. Instrum. 20, P12018 (2025).
  138. R. Mammen Abraham et al. (FASER Collaboration), First measurement of νe and νμ interaction cross sections at the LHC with FASER’s emulsion detector, Phys. Rev. Lett. 133, 021802 (2024).
  139. A. Ariga et al. (FASER Collaboration), Letter of intent for FASER: ForwArd search experiment at the LHC, arXiv:1811.10243.
  140. A. Ariga et al. (FASER Collaboration), Technical proposal for FASER: Forward search experiment at the LHC, arXiv:1812.09139.
  141. A. Ariga et al. (FASER Collaboration), FASER’s physics reach for long-lived particles, Phys. Rev. D 99, 095011 (2019).
  142. A. Ariga et al. (FASER Collaboration), FASER: Forward search experiment at the LHC, arXiv:1901.04468.
  143. H. Abreu et al. (FASER Collaboration), The tracking detector of the FASER experiment, Nucl. Instrum. Methods Phys. Res., Sect. A 1034, 166825 (2022).
  144. H. Abreu et al. (FASER Collaboration), Search for dark photons with the FASER detector at the LHC, Phys. Lett. B 848, 138378 (2024).
  145. 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.
  146. O. Adriani et al. (LHCf Collaboration), Measurement of inclusive forward neutron production cross section in proton-proton collisions at s=13  TeV with the LHCf Arm2 detector, J. High Energy Phys. 11 (2018) 073.
  147. T. Pierog, I. Karpenko, J. M. Katzy, E. Yatsenko, and K. Werner, EPOS LHC: Test of collective hadronization with data measured at the CERN large hadron collider, Phys. Rev. C 92, 034906 (2015).
  148. F. Riehn, R. Engel, A. Fedynitch, T. K. Gaisser, and T. Stanev, Hadronic interaction model Sibyll 2.3d and extensive air showers, Phys. Rev. D 102, 063002 (2020).
  149. S. Ostapchenko, Monte Carlo treatment of hadronic interactions in enhanced Pomeron scheme: I. QGSJET-II model, Phys. Rev. D 83, 014018 (2011).
  150. F. Kling and S. Trojanowski, Forward experiment sensitivity estimator for the LHC and future hadron colliders, Phys. Rev. D 104, 035012 (2021).
  151. L. Heinrich, M. Feickert, G. Stark, and K. Cranmer, pyhf: Pure-python implementation of HistFactory statistical models, J. Open Source Software 6, 2823 (2021).
  152. H. Merkel et al., Search at the mainz microtron for light massive gauge bosons relevant for the muon g-2 anomaly, Phys. Rev. Lett. 112, 221802 (2014).
  153. J. P. Lees et al. (BABAR Collaboration, Search for a dark photon in e+e− collisions at BABAR, Phys. Rev. Lett. 113, 201801 (2014).
  154. J. R. Batley et al. (NA48/2 Collaboration), Search for the dark photon in π0 decays, Phys. Lett. B 746, 178 (2015).
  155. 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).
  156. E. Cortina Gil et al. (NA62 Collaboration), Search for leptonic decays of dark photons at NA62, Phys. Rev. Lett. 133, 111802 (2024).
  157. A. L. Foguel, P. Reimitz, and R. Z. Funchal, A robust description of hadronic decays in light vector mediator models, J. High Energy Phys. 04 (2022) 119.
  158. F. Bergsma et al. (CHARM Collaboration), Search for axion like particle production in 400-GeV proton—copper interactions, Phys. Lett. B 157, 458 (1985).
  159. M. Davier and H. Nguyen Ngoc, An unambiguous search for a light Higgs boson, Phys. Lett. B 229, 150 (1989).
  160. 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).
  161. P. Ilten, Y. Soreq, M. Williams, and W. Xue, Serendipity in dark photon searches, J. High Energy Phys. 06 (2018) 004.
  162. P. Vilain et al. (CHARM-II Collaboration), Measurement of differential cross-sections for muon-neutrino electron scattering, Phys. Lett. B 302, 351 (1993).
  163. S. Bilmis, I. Turan, T. M. Aliev, M. Deniz, L. Singh, and H. T. Wong, Constraints on dark photon from neutrino-electron scattering experiments, Phys. Rev. D 92, 033009 (2015).
  164. Y. M. Andreev et al. (NA64 Collaboration), Search for a new B-L Z’ gauge boson with the NA64 experiment at CERN, Phys. Rev. Lett. 129, 161801 (2022).
  165. J. Blumlein et al., Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment, Z. Phys. C 51, 341 (1991).
  166. A. Anastasi et al., Limit on the production of a low-mass vector boson in e+e−→Uγ, U→e+e− with the KLOE experiment, Phys. Lett. B 750, 633 (2015).
  167. D. Babusci et al. (KLOE-2 Collaboration), Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector, Phys. Lett. B 720, 111 (2013).
  168. R. Aaij et al. (LHCb Collaboration), Search for dark photons produced in 13 TeV pp collisions, Phys. Rev. Lett. 120, 061801 (2018).
  169. R. Aaij et al. (LHCb Collaboration), Search for A′→μ+μ− decays, Phys. Rev. Lett. 124, 041801 (2020).
  170. J. A. Dror, R. Lasenby, and M. Pospelov, New constraints on light vectors coupled to anomalous currents, Phys. Rev. Lett. 119, 141803 (2017).
  171. J. L. Feng, B. Fornal, I. Galon, S. Gardner, J. Smolinsky, T. M. P. Tait, and P. Tanedo, Particle physics models for the 17 MeV anomaly in beryllium nuclear decays, Phys. Rev. D 95, 035017 (2017).
  172. J. L. Feng, T. M. P. Tait, and C. B. Verhaaren, Dynamical evidence for a fifth force explanation of the ATOMKI nuclear anomalies, Phys. Rev. D 102, 036016 (2020).
  173. A. J. Krasznahorkay et al., Observation of anomalous internal pair creation in Be8: A possible indication of a light, neutral boson, Phys. Rev. Lett. 116, 042501 (2016).
  174. D. S. Firak et al., Confirmation of the existence of the X17 particle, EPJ Web Conf. 232, 04005 (2020).
  175. D. S. M. Alves et al., Shedding light on X17: Community report, Eur. Phys. J. C 83, 230 (2023).
  176. P. S. B. Dev, B. Dutta, T. Han, A. Karthikeyan, D. Kim, and H. Kim, New physics at a neutron beam dump, Phys. Rev. D 110, L051703 (2024).
  177. A. Anastasi et al. (KLOE-2 Collaboration), Combined limit on the production of a light gauge boson decaying into μ+μ− and π+π−, Phys. Lett. B 784, 336 (2018).
  178. F. Bossi et al., Search for a new 17 MeV resonance via e+e− annihilation with the PADME experiment, J. High Energy Phys. 11 (2025) 007.
  179. E. M. Riordan et al., A search for short lived axions in an electron beam dump experiment, Phys. Rev. Lett. 59, 755 (1987).
  180. F. Arias-Aragón, G. G. di Cortona, E. Nardi, and C. Toni, Combined evidence for the X17 boson after PADME results on resonant production in positron annihilation, arXiv:2504.11439.
  181. B. Holdom, Two U(1)’s and epsilon charge shifts, Phys. Lett. 166B, 196 (1986).
  182. S. Foroughi-Abari, F. Kling, and Y.-D. Tsai, Looking forward to millicharged dark sectors at the LHC, Phys. Rev. D 104, 035014 (2021).
  183. A. Haas, C. S. Hill, E. Izaguirre, and I. Yavin, Looking for milli-charged particles with a new experiment at the LHC, Phys. Lett. B 746, 117 (2015).
  184. A. Ball et al., A letter of intent to install a milli-charged particle detector at LHC P5, arXiv:1607.04669.
  185. A. Ball et al. (milliQan Collaboration), Sensitivity to millicharged particles in future proton-proton collisions at the LHC with the milliQan detector, Phys. Rev. D 104, 032002 (2021).
  186. S. N. Gninenko, D. V. Kirpichnikov, and N. V. Krasnikov, Probing millicharged particles with NA64 experiment at CERN, Phys. Rev. D 100, 035003 (2019).
  187. G. Marocco and S. Sarkar, Blast from the past: Constraints on the dark sector from the BEBC WA66 beam dump experiment, SciPost Phys. 10, 043 (2021).
  188. A. A. Prinz et al., Search for millicharged particles at SLAC, Phys. Rev. Lett. 81, 1175 (1998).
  189. S. Davidson, S. Hannestad, and G. Raffelt, Updated bounds on millicharged particles, J. High Energy Phys. 05 (2000) 003.
  190. R. Akers et al. (OPAL Collaboration), Search for heavy charged particles and for particles with anomalous charge in e+e− collisions at LEP, Z. Phys. C 67, 203 (1995).
  191. S. Chatrchyan et al. (CMS Collaboration), Search for fractionally charged particles in pp collisions at s=7  TeV, Phys. Rev. D 87, 092008 (2013); 106, 099903(E) (2022).
  192. J. Jaeckel, M. Jankowiak, and M. Spannowsky, LHC probes the hidden sector, Phys. Dark Universe 2, 111 (2013).
  193. A. Hayrapetyan et al. (CMS Collaboration), Search for fractionally charged particles in proton-proton collisions at s=13  TeV, Phys. Rev. Lett. 134, 131802 (2025).
  194. G. Magill, R. Plestid, M. Pospelov, and Y.-D. Tsai, Millicharged particles in neutrino experiments, Phys. Rev. Lett. 122, 071801 (2019).
  195. R. Acciarri et al. (ArgoNeuT Collaboration), Improved limits on millicharged particles using the argoneut experiment at Fermilab, Phys. Rev. Lett. 124, 131801 (2020).
  196. A. Ball et al., Search for millicharged particles in proton-proton collisions at s=13  TeV, Phys. Rev. D 102, 032002 (2020).
  197. S. Alcott et al., Search for millicharged particles in proton-proton collisions at s=13.6  TeV, Phys. Rev. Lett. 135, 121802 (2025).
  198. L. Barak et al. (SENSEI Collaboration), Search by the SENSEI experiment for millicharged particles produced in the NuMI beam, Phys. Rev. Lett. 133, 071801 (2024).
  199. P. Ilten et al., Experiments and facilities for accelerator-based dark sector searches, in Snowmass 2021 (2022), arXiv:2206.04220.
  200. 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).
  201. C. Ahdida et al., Post-LS3 experimental options in ECN3, arXiv:2310.17726.

Outline

Information

Phys. Rev. D 113, 015008– Published 8 January, 2026
  • Received 30 September 2025
  • Accepted 15 December 2025
Crossmark - Check for updates button
Creative Commons Logo

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

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation