Search for light vector boson production in $e^+e^- \rightarrow \mu^+ \mu^- \gamma$ interactions with the KLOE experiment

TL;DR

This study searches for a hypothetical light vector boson 'U' in electron-positron collisions producing muon pairs and a photon, but finds no evidence and sets upper limits on its possible coupling strength within a specific mass range.

Contribution

First search for the light vector boson 'U' in the extit{e+e-} to extit{ extmu+ extmu-} extgamma eaction using the KLOE detector, establishing new upper limits on its coupling.

Findings

No evidence of the 'U' boson signal was observed.

Set upper limits on the mixing parameter squared between photon and 'U' boson.

Limits range from 1.6×10^{-5} to 8.6×10^{-7} for 520-980 MeV mass.

Abstract

We have searched for a light vector boson $U$, the possible carrier of a "dark force", with the KLOE detector at the DA$\Phi$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$\mu^+ \mu^-$\gam, corresponding to the decay $U\to\mu^+\mu^-$. 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 $520<m_{\rm U}<980$ MeV.