Updated E141 constraints on a long-lived X17 vector boson
Abstract
Since its first observation by the ATOMKI experiment in 2018, the ^*Be anomaly has attracted considerable interest within the dark sector community as it may indicate the existence of a new fundamental particle with a mass of about 16.9 MeV, the X17. However, the minimal model describing X17 as a new vector boson is severely constrained by null results from legacy beam-dump experiments. Among these, the E141 experiment at SLAC places stringent limits on the X17 coupling to electrons εe in the 5.1×10−5≲ εe≲1.7×10−4 region. This excludes the possibility of a long-lived X17, potentially in contrast with the preliminary estimate of the particle lifetime recently reported by the ATOMKI collaboration. The E141 limits commonly adopted in the literature rely on reinterpretations of the original analysis under solid but simplifying assumptions. While these studies provide a reliable estimate of the experiment's reach, they rely on approximations that were well justified when the boson mass was largely unconstrained. With the X17 mass now confined to a narrow region by recent experimental observations, a more refined treatment of the E141 sensitivity becomes necessary. In this work, we revisit the E141 exclusion limits in the X17 scenario by performing a dedicated reanalysis that incorporates a more accurate treatment of the experimental setup and signal prediction. We quantify the impact of these refinements on the excluded parameter space and discuss their implications for the compatibility between the E141 constraints and the vector boson interpretation of the ATOMKI anomalies.
Related
- Constraints on a Long-Lived X17 Vector Boson with FASER
- Probing pair production of long-lived scalars via an off-shell Standard-Model-like Higgs boson at the LHC
- One-loop QCD amplitudes for vector-boson-fusion Higgs-boson production to higher orders in ε
- Next-to-Leading-Order Multi-Jet Merging of Higgs Boson Production via Vector Boson Fusion in the Presence of Anomalous Couplings
- Two Feynman integral families for vector boson fusion at NNLO QCD
BibTeX
@misc{celentano2026updated,
title = {{Updated E141 constraints on a long-lived $X_17$ vector boson}},
author = {A. Celentano and A. Marini and L. Marsicano},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.22102},
eprint = {2607.22102},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.22102},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Updated E141 constraints on a long-lived X_17 vector boson
AU - A. Celentano
AU - A. Marini
AU - L. Marsicano
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2607.22102
UR - https://arxiv.org/abs/2607.22102
AB - Since its first observation by the ATOMKI experiment in 2018, the ^*Be anomaly has attracted considerable interest within the dark sector community as it may indicate the existence of a new fundamental particle with a mass of about 16.9 MeV, the X_17. However, the minimal model describing X_17 as a new vector boson is severely constrained by null results from legacy beam-dump experiments. Among these, the E141 experiment at SLAC places stringent limits on the X_17 coupling to electrons ε_e in the 5.1×10^−5≲ ε_e≲1.7×10^−4 region. This excludes the possibility of a long-lived X_17, potentially in contrast with the preliminary estimate of the particle lifetime recently reported by the ATOMKI collaboration. The E141 limits commonly adopted in the literature rely on reinterpretations of the original analysis under solid but simplifying assumptions. While these studies provide a reliable estimate of the experiment's reach, they rely on approximations that were well justified when the boson mass was largely unconstrained. With the X_17 mass now confined to a narrow region by recent experimental observations, a more refined treatment of the E141 sensitivity becomes necessary. In this work, we revisit the E141 exclusion limits in the X_17 scenario by performing a dedicated reanalysis that incorporates a more accurate treatment of the experimental setup and signal prediction. We quantify the impact of these refinements on the excluded parameter space and discuss their implications for the compatibility between the E141 constraints and the vector boson interpretation of the ATOMKI anomalies.
ER -