  The Heavy Photon Search experiment (HPS) at Jefferson Laboratory will search
for a new $U(1)$ massive gauge boson, or "heavy-photon," mediator of a new
fundamental interaction, called "dark-force," that couples to ordinary photons
trough kinetic mixing. HPS has sensitivity in the mass range 20 MeV - 1 GeV and
coupling $\varepsilon^2$ between 10$^{-5}$ and 10$^{-10}$. The HPS experiment
will search for the $e^+e^-$ decay of the heavy photon, by resonance search and
detached vertexing, in an electron beam fixed target experiment. HPS will use a
compact forward spectrometer, which employs silicon microstrip detectors for
vertexing and tracking, and a PbWO$_4$ electromagnetic calorimeter for energy
measurement and fast triggering.
