Constraints on a Long-Lived X17 Vector Boson with FASER

@misc{collaboration2026constraints,
  title = {{Constraints on a Long-Lived X17 Vector Boson with FASER}},
  author = {FASER Collaboration and Roshan Mammen Abraham and Xiaocong Ai and Saul Alonso Monsalve and John Anders and Emma Kate Anderson and Akitaka Ariga and Tomoko Ariga and Jeremy Atkinson and Florian U. Bernlochner and Jianming Bian and Tobias Boeckh and Eliot Bornand and Jamie Boyd and Lydia Brenner and Angela Burger and Franck Cadoux and Haichuan Cao and Roberto Cardella and David W. Casper and Charlotte Cavanagh and Shiyang Chen and Xin Chen and Xing Cheng and Dhruv Chouhan and Emily Chown and Andrea Coccaro and Fabio Cufino and Stephane Débieux and Ansh Desai and Sergey Dmitrievsky and Radu Dobre and Monica D'Onofrio and Sinead Eley and Yannick Favre and Jonathan L. Feng and Carlo Alberto Fenoglio and Didier Ferrere and Max Fieg and Wissal Filali and Elena Firu and Haruhi Fujimori and Edward Galantay and Ali Garabaglu and Stephen Gibson and Sergio Gonzalez-Sevilla and Yuri Gornushkin and Yotam Granov and Jinjing Gu and Carl Gwilliam and Elie Hammou and Daiki Hayakawa and Michael Holzbock and Shih-Chieh Hsu and Zhen Hu and Giuseppe Iacobucci and Tomohiro Inada and Luca Iodice and Sune Jakobsen and Cesar Jesus-Valls},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.03904},
  eprint = {2611.03904},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.03904},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Constraints on a Long-Lived X17 Vector Boson with FASER
AU  - FASER Collaboration
AU  - Roshan Mammen Abraham
AU  - Xiaocong Ai
AU  - Saul Alonso Monsalve
AU  - John Anders
AU  - Emma Kate Anderson
AU  - Akitaka Ariga
AU  - Tomoko Ariga
AU  - Jeremy Atkinson
AU  - Florian U. Bernlochner
AU  - Jianming Bian
AU  - Tobias Boeckh
AU  - Eliot Bornand
AU  - Jamie Boyd
AU  - Lydia Brenner
AU  - Angela Burger
AU  - Franck Cadoux
AU  - Haichuan Cao
AU  - Roberto Cardella
AU  - David W. Casper
AU  - Charlotte Cavanagh
AU  - Shiyang Chen
AU  - Xin Chen
AU  - Xing Cheng
AU  - Dhruv Chouhan
AU  - Emily Chown
AU  - Andrea Coccaro
AU  - Fabio Cufino
AU  - Stephane Débieux
AU  - Ansh Desai
AU  - Sergey Dmitrievsky
AU  - Radu Dobre
AU  - Monica D'Onofrio
AU  - Sinead Eley
AU  - Yannick Favre
AU  - Jonathan L. Feng
AU  - Carlo Alberto Fenoglio
AU  - Didier Ferrere
AU  - Max Fieg
AU  - Wissal Filali
AU  - Elena Firu
AU  - Haruhi Fujimori
AU  - Edward Galantay
AU  - Ali Garabaglu
AU  - Stephen Gibson
AU  - Sergio Gonzalez-Sevilla
AU  - Yuri Gornushkin
AU  - Yotam Granov
AU  - Jinjing Gu
AU  - Carl Gwilliam
AU  - Elie Hammou
AU  - Daiki Hayakawa
AU  - Michael Holzbock
AU  - Shih-Chieh Hsu
AU  - Zhen Hu
AU  - Giuseppe Iacobucci
AU  - Tomohiro Inada
AU  - Luca Iodice
AU  - Sune Jakobsen
AU  - Cesar Jesus-Valls
PY  - 2026
DA  - 2026/11/02
PB  - arXiv
DO  - 10.48550/arxiv.2611.03904
UR  - https://arxiv.org/abs/2611.03904
AB  - The ATOMKI anomalies motivate the possibility of a new particle, the X17, with a mass of 17 MeV and weak couplings to nuclei and electrons. Such a particle may be produced at the LHC, travel 480 m in the far-forward direction, and decay to e^+e^- in FASER. In this paper, previous FASER searches for dark photons and axion-like particles (ALPs) are combined and interpreted as searches for a candidate X17 particle, the protophobic vector boson. The searches use data collected from pp collisions at √s = 13.6 TeV in LHC Run 3 from 2022 for the dark photon search and from 2022-2023 for the ALP search. No excess events are found above the expected background, and the combined null results exclude a previously-unconstrained "low-coupling window" with electron coupling 6 × 10^−5 < ε_e < 1.2 × 10^−4. A "high-coupling window" remains.
ER  -