A Proposal for the DarkLight Experiment at the Jefferson Laboratory Free Electron Laser

New theories of dark matter predict A gauge bosons in the mass range of 0.01– 10 GeV that couple to charged fermions with a strength of α /α EM = 10 −4 of the photon or less. We propose to design, construct and operate an experiment called DarkLight (Detecting A Resonance Kinematically with eLectrons Incident on a Gaseous Hydrogen Target) to use the 1 MW 100 MeV electron beam at the Jeffer-son Lab Free Electron Laser incident on a 10 19 cm 2 thick target to study the process e − +p → e − +p+e − +e +. A dark force particle would show up as a narrow resonance in the radiated e + − e − system. Our experiment would explore the A mass region 10-100 MeV and couplings as low as α ∼ 10 −9 with 1/ab of data, which would require 60 days of data taking (assuming 100% efficiency) at the Jefferson Lab Free Electron Laser. We also plan for 30 days of running (assuming 100% efficiency) for beam studies, calibration and commissioning.