Measuring a long-range dark matter force at the Large Hadron Collider.

A long-range "dark force" has recently been proposed to mediate the dark matter (DM) annihilation. If DM particles are copiously produced at the Large Hadron Collider, the light dark force mediator will also be produced through radiation. We demonstrate how and how precise we can utilize this fact to measure the coupling constant of the dark force. The light mediator's mass is measured for the "lepton jet" to which it decays. In addition, the mass of the DM particle is determined using the m(T2) technique. Knowing these quantities is critical for calculating the DM relic density.