Abstract
The dark photon and the dark Higgs boson are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel , with . We investigate ten exclusive final states with , , or in the mass ranges and . We also investigate three inclusive final states , , and , where denotes a dark photon candidate detected via missing mass, in the mass ranges and . Using the entire data set collected by Belle, we observe no significant signal. We obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, , on the Born cross section , and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, . These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states and are the first placed by any experiment. For equal to , , and , we exclude values of the mixing parameter above .
- Received 31 January 2015
DOI:https://doi.org/10.1103/PhysRevLett.114.211801
© 2015 American Physical Society