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