Constraints on dark photons from $\pi^0$ decays

Understand

Several models of dark matter suggest the existence of hidden sectors consisting of SU(3)_C x SU(2)_L x U(1)_Y singlet fields.

• The interaction between the ordinary and hidden sectors could be transmitted by new Abelian U'(1) gauge bosons A' (dark or hidden photons) mixing with ordinary photons.
• If such A's have masses below the \pi^0 meson mass, they would be produced through \gamma - A' mixing in the \pi^0 ->2\gamma - decays and be observed via their decays A' -> e+e- in a detector.
• Using bounds from the SINDRUM experiment at the Paul Scherrer Institute that searched for an excess of e+e- pairs in \pi^- p interactions at rest, the area excluding the \gamma - A' mixing \epsilon > 10^{-3} for the A' mass region 25 < M_{A'} < 120 MeV is derived.