Searching hidden-sector photons inside a superconducting box

We propose an experiment to search for extra hidden-sector U(1) gauge bosons with small gauge kinetic mixing chi with the ordinary photon, predicted by many extensions of the Standard Model. The setup consists of a highly sensitive magnetometer inside a superconducting shielding which are in turn placed inside a strong (but sub-critical) magnetic field. Photon - hidden-sector photon - photon oscillations would allow the magnetic field to leak into the shielded volume and register on the magnetometer. In our setup the magnetometer directly measures the field strength (alpha chi(2)), improving the sensitivity over light-shining-through-walls experiments which measure the regeneration probability (alpha chi(4)). In the mass range 2 mu eV less than or similar to m(gamma') less than or similar to 200meV the projected sensitivity is in the chi similar to 5 x 10(-9) to chi similar to 10(-6) range. This surpasses current astrophysical and laboratory limits by several orders of magnitude - ample room to discover new physics. Copyright (C) EPLA, 2008