Search for a vector gauge boson in φ meson decays with the KLOE detector

The existence of a light dark force mediator has been tested with the KLOE detector at DAΦNE. This particle, called U, is searched for using the decay chain φ→ηU, η→π+π-π0, U→e+e-. No evidence is found in 1.5 fb-1 of data. The resulting exclusion plot covers the mass range 5<MU<470 MeV, setting an upper limit on the ratio between the U boson coupling constant and the fine structure constant, α'/α, of ≤2×10-5 at 90% C.L. for 50<MU<420 MeV. © 2011 Elsevier B.V.