Search for the U-boson in the process $e^ +e^- \to \mu^+ \mu^- \gamma, \,\, U \to \mu^+\mu^-$ with the KLOE detector

TL;DR

This study searched for a hypothetical U-boson in electron-positron collisions producing muon pairs and a photon, but found no evidence, setting upper limits on its coupling strength within a specific mass range.

Contribution

First search for the U-boson in the muon channel using the KLOE detector, establishing new upper limits on its coupling constants in the 520-980 MeV mass range.

Findings

No U-boson signal detected.

Set upper limits on U-boson coupling constants.

Projected increased sensitivity with full data set.

Abstract

We present a search for a new light vector boson, carrier of a "dark force" between WIMPs, with the KLOE detector at \DA$\Phi$NE. We analyzed $e^+ e^- \to \mu^+ \mu^- \gamma$ ISR events corresponding to an integrated luminosity of $239$ pb$^{-1}$ to find evidence for the $e^+ e^- \to U\gamma ,\,\, U\to\mu^+\mu^-$ process. We found no $U$ vector boson signal and set a 90% CL upper limit on the ratio of the U boson and photon coupling constants between 1.6$\times10^{-5}$ to 8.6$\times10^{-7}$ in the mass region $520<M_{\rm U}<980$ MeV. A projection of the KLOE sensitivity for the $\mu\mu\gamma$ and $\pi\pi\gamma$ channels at full statistics and extended muon acceptance is also presented.