Search for a muonic dark force at BABAR

TL;DR

This paper reports a search for a hypothetical dark sector gauge boson Z' that couples to muons, using BABAR data, setting new limits on its coupling strength in the 0.212-10 GeV mass range.

Contribution

The study provides the first search for a Z' boson coupling only to second and third generation leptons in electron-positron collisions, improving existing bounds.

Findings

No significant Z' signal observed in the mass range 0.212-10 GeV.

Set upper limits on the coupling parameter g' as low as 7x10^-4.

Improved constraints compared to previous neutrino experiment bounds.

Abstract

Many models of physics beyond the Standard Model predict the existence of new Abelian forces with new gauge bosons mediating interactions between "dark sectors" and the Standard Model. We report a search for a dark boson Z' coupling only to the second and third generations of leptons in the reaction e+e- -> mu+mu- Z', Z' -> mu+mu- using 514 fb-1 of data collected by the BABAR experiment. No significant signal is observed for Z' masses in the range 0.212 - 10 GeV. Limits on the coupling parameter g' as low as 7x10^-4 are derived, leading to improvements in the bounds compared to those previously derived from neutrino experiments.