Search for light vector boson production in $e^{+}{e}^{-}\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}{\hat{I}}^3$ interactions with the KLOE experiment

Abstract

We have searched for a light vector boson $U$, the possible carrier of a "dark force", with the KLOE detector at the DA$\hat{I}¦$NE \epm\ collider, motivated by astrophysical evidence for the presence of dark matter in the universe. Using \epm\ collisions collected with an integrated luminosity of $239.3$~pb${}^{-1}$, we look for a dimuon mass peak in the reaction \epm\to$\hat{I}{¼}^{+}\hat{I}{¼}^{-}$\gam, corresponding to the decay $U\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$. We find no evidence for a $U$ vector boson signal. We set a 90\% CL upper limit for the mixing parameter squared between the photon and the $U$ boson of 1.6$\times$10${}^{-5}$ to 8.6$\times$10${}^{-7}$ for the mass region $520<m_{\mathrm{U}}<980$ MeV.

12 pages, 7 figures, version accepted for publication in Physics Letters B