Search for dark forces with KLOE

During the last years several Dark Sector Models have been proposed in order to address striking astrophysical observations which failed standard interpretations. In the minimal case a new vector particle, the so called dark photon, or A′ or U boson, is introduced, with small coupling with Standard Model particles. Also, the existence of a dark Higgs boson h′ is postulated, in analogy with the Standard Model, to give mass to the U boson through the Spontaneous Symmetry Breaking mechanism. The KLOE experiment working at DAΦNE, an e⁺e⁻ collider operating in Frascati (near Rome), searched for the existence of the U boson investigating three different processes and six different final states: (1) in Dalitz decays of the ϕ meson ϕ → ηU, with U → e⁺e⁻ and η → π⁺π⁻π⁰ and π⁰π⁰π⁰, (2) in e⁺e⁻ → Uh′ events, with U decaying into lepton and pion pairs, (3) in the dark Higgsstrahlung process, e⁺e⁻ → Uh′, U → μ⁺μ⁻, h′ invisible. Limits on the model parameters have been set at 90 % CL for U boson masses below 1 GeV. Further improvements are expected in terms of sensitivity and discovery potential with the new KLOE-2 detector.