Interference-assisted detection of dark photon using atomic transitions

Dark photon is a massive vector particle which couples to the physical photon through the kinetic mixing term. Such particles, if they exist, are produced in photon beams and, in particular, in laser radiation. Because of the oscillations between the physical photon and the dark photon, the latter may be, in principle, detected in the light-shining-through-a-wall experiment. We propose a variant of this experiment in which the detection of dark photons is based on the atomic transitions. The key feature of this scheme is that the detection probability is first order in the coupling constant due to the interference term in the photon and dark photon absorption amplitudes. We expect that such an experiment may give new constraints on the dark photon coupling constant in the mass region ${10}^{-3}<m<{10}^{-2}\mathrm{eV}$.

Figure 1

Experiment setup. The dashed (blue) line corresponds to the dark photon beam ${\gamma }^{\prime }$, while the solid (red) lines represent the photon beams ${\gamma }_1$ and ${\gamma }_2$.

Figure 2

Comparison of constraints on the dark photon coupling constant from different LSW-type experiments. The purple thin line corresponds to the GammeV experiment, the brown dotted-dashed line corresponds to the BMV experiment, the blue dotted line corresponds to the BFRT experiment, the yellow dashed line corresponds to the OSQAR experiment, and the red thick line represents possible constraints from the experimental setup proposed in this paper based on the interference between the photon and dark photon amplitudes. The short-dashed black line shows expected results from the ALPS-II experiment. The new (pink) exclusion region improves the constraints from other SLW experiments in the region of the dark photon mass ${10}^{-3}<m<{10}^{-2}\mathrm{eV}$.