Search for very light neutral spin-zero bosons at optical frequencies.

A Hampton-Jefferson Lab-Yale collaboration is working on an experiment (LIPSS) to test one interpretation of the PVLAS experiment. The PVLAS experiment detected a rotation of the plane of polarization of light in a magnetic field in a vacuum. This can be interpreted as due to the production of a very light (meV) neutral boson that couples to two photons. Such a boson would be outside the Standard Model. The LIPSS experiment is looking for the two-step process in which bosons are generated in a magnetic field by a laser beam and then photons are regenerated by the bosons in a second magnetic field. The status of the experiment, being carried out at the Jefferson Lab Free-Electron Laser User Facility, will be reported.