Dark photon limits: A handbook

The dark photon is a massive hypothetical particle that interacts with the Standard Model by kinetically mixing visible photon. For small values of parameter, photons can evade cosmological bounds to be viable matter candidate. Due similarities electromagnetic signals generated axions, several on are simply reinterpretations historical set axion haloscopes. However, has property does not: an intrinsic polarisation. rotation Earth, accurately accounting for this polarisation nontrivial, highly experiment-dependent, and depends upon assumptions about photon's production mechanism. We show if one account DP polarisation, experiment's discovery reach enhanced over order magnitude. detail strategies would need taken properly optimise search. These include judiciously choosing location orientation experiment, as well strategically timing any repeated measurements. Experiments located at $\pm$35$^\circ$ or $\pm$55$^\circ$ latitude, making three observations different times sidereal day, achieve sensitivity fully optimised insensitive state, hence its also point out well-known searches axions employ techniques testing preclude their ability exclusion limits photons, should not reinterpreted such.