Physical Review C
The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g-2)μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π0,η→γe+e- decays and obtained upper limits of O(2×10‐⁶) U-γ mixing at 90% C.L. for the mass range 30< mᵤ < 90 MeV/c². Combined with other experimental limits, the remaining region in the U-γ mixing parameter space that can explain the (g-2)ᵤ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29
Adare, Andrew Marshall; Baksay, Gyöngyi; Baksay, László A.; Hohlmann, Marcus; Rembeczki, S.; and PHENIX Collaboration, "Search For Dark Photons From Neutral Meson Decays In p+p And d+ Au Collisions At √sNN =200 GeV" (2015). Aerospace, Physics, and Space Science Faculty Publications. 447.