Photon Regeneration from Pseudoscalars at X-Ray Laser Facilities

Recently, the PVLAS Collaboration reported an anomalously large rotation of the polarization of light in the presence of a magnetic field in vacuum. As a possible explanation, they consider the existence of a light spin-zero particle coupled to two photons. We propose here a method of independently testing this result using a high-energy photon regeneration experiment (the x-ray analogue of “invisible light shining through walls”) using the synchrotron x rays from a free-electron laser. With such an experiment the region of parameter space implied by PVLAS could be probed in a matter of minutes.

Figure 1

Schematic figure of the regeneration experiment.

Figure 2

95% confidence level exclusion region for different running times: 1 d and 1 yr for two different magnets (a conventional magnet with $L=20\mathrm{m}$ and $B=1\mathrm{T}$ and a superconducting magnet with $L=10\mathrm{m}$ and $B=10\mathrm{T}$). We have assumed efficient (perfect) x-ray detection and an x-ray beam with $N_0={10}^{17}{\mathrm{s}}^{-1}$ and $\omega =10\mathrm{keV}$. Note that photons with energies as low as $\sim 30\mathrm{eV}$ would be adequate for testing PVLAS without being limited by incoherent effects.