2025/10/18 by BESIII Collaboration, Ablikim, M., Achasov, M. N. +678 · 1 citation
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2510.16531
We report a direct search for a new gauge boson, X, with a mass of 17~MeV/c2, which could explain the anomalous excess of e+e- pairs observed in the 8Be nuclear transitions. The search is conducted in the charmonium decay χcJ→ X J/ψ~(J=0,1,2) via the radiative transition ψ(3686)→γχcJ using (2712.4± 14.3 )× 106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the new upper limit on the coupling strength of charm quark and the new gauge boson, εc, at 17~MeV/c2 is set to be |εc|<1.2× 10-2 at 90% confidence level. We also report new constraints on the mixing strength ε between the Standard Model photon and dark photon γ^′ in the mass range from 5~MeV/c2 to 300~MeV/c2. The upper limits at 90% confidence level vary within (2.5-17.5)× 10-3 depending on the γ^′ mass.