Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays

TL;DR

This paper uses data from the CHARM experiment to set new limits on hypothetical sub-GeV gauge bosons that could mediate interactions between hidden sectors and standard matter, improving constraints on their properties.

Contribution

It provides the first experimental bounds on the mixing parameter  and mass range for hidden sector gauge bosons using neutrino experiment data, and tightens constraints on ' and ' related models.

Findings

Excluded ' mixing range 10^{-7} to 10^{-4} for masses 1-500 MeV.

Set upper limits on ta rrow  ' decay branching ratios.

Improved bounds on ta, ta' decays involving new gauge bosons.

Abstract

Several models of dark matter motivate the concept of hidden sectors consisting of SU(3)_C x SU(2)_L x U(1)_Y singlet fields. The interaction between our and hidden matter could be transmitted by new abelian U'(1) gauge bosons A' mixing with ordinary photons. If such A's with the mass in the sub-GeV range exist, they would be produced through mixing with photons emitted in two photon decays of \eta,\eta' neutral mesons generated by the high energy proton beam in a neutrino target. The A's would then penetrate the downstream shielding and be observed in a neutrino detector via their A'-> e+e- decays. Using bounds from the CHARM neutrino experiment at CERN that searched for an excess of e+e- pairs from heavy neutrino decays, the area excluding the \gamma - A' mixing range 10^{-7} < \epsilon < 10^{-4} for the A' mass region 1 < M_A' <500 MeV is derived. The obtained results are also used to constrain models, where a new gauge boson X interacts with quarks and leptons. New upper limits on the branching ratio as small as Br(\eta -> \gamma X) < 10^{-14} and Br(\eta' -> \gamma X) < 10^{-12} are obtained, which are several orders of magnitude more restrictive than the previous bounds from the Crystal Barrel experiment.