Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector

TL;DR

This paper sets new upper limits on the production of a hypothetical light vector gauge boson in phi meson decays, using data from the KLOE detector, without observing any signal over background.

Contribution

It provides the first combined analysis of two decay channels to improve sensitivity and establishes the most stringent limits to date on the U boson coupling in the specified mass range.

Findings

No evidence of the U boson was observed.

Upper limits on the coupling ratio were set at 1.7x10^-5 and 8x10^-6.

The results depend on the assumed transition form factor.

Abstract

We present a new limit on the production of a light dark-force mediator with the KLOE detector at DAPHNE. This boson, called U, has been searched for in the decay phi --> eta U, U --> e+ e-, analyzing the decay eta --> pi0 pi0 pi0 in a data sample of 1.7 fb-1. No structures are observed in the e+e- invariant mass distribution over the background. This search is combined with a previous result obtained from the decay eta --> pi+ pi- pi0, increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of alpha'/alpha < 1.7x10^-5 for 30<M_U<400 MeV and alpha'/alpha < 8x10^-6 for the sub-region 50<M_U<210 MeV. This result assumes the Vector Meson Dominance expectations for the phietagamma^* transition form factor. The dependence of this limit on the transition form factor has also been studied.