Projects: GammeV
The GammeV experiment is a gamma to milli-eV particle search using a "light shining through a wall" technique. Recently, the PVLAS collaboration has reported measurements of anomalous vacuum magnetic dichroism or polarization rotation and birefringence or polarization ellipticity generation which, when interpreted as a new two-photon interaction, imply new resonances of the vacuum at the milli-eV scale with a coupling constant between 10-6 and 10-5 GeV-1. This meV scale particle would be an axion-like particle (ALP) but with a much stronger coupling than expected for the QCD axion.
The ALP interpretation of the PVLAS data can be tested in our "light shining through a wall" experiment where a photon in a high magnetic field can convert into an ALP, travel through the "wall¨ and then reconvert back into a photon on the other side. Such an experiment was performed by the BFRT collaboration in the early 1990s. However, that experiment happened to be minimally sensitive in the PVLAS region of interest. This is because the probability for a photon to be regenerated depends on the length of the traversal in the magnetic field and BFRT happened to use a magnet which gave a result with minimal sensitivity in the meV mass range exactly where the PVLAS signal would suggest a new resonance may occur.
The GammeV experiment uses a spare Tevatron magnet whose length is such that it can test the PVLAS region of interest in an efficient manner with the potential of being the first experimental test world-wide of the expected photon regeneration process assuming the new milli-eV particle interpretation. The "wall" in our apparatus is attached to a moveable plunger which allows us to adjust the path length in the magnetic field, and hence probe for ALP's of different masses.
In addition to the ALP search, a slight modification to our experiment allows us to manufacture and trap chameleon or dilaton particles (particles whose interactions with matter depend upon the local matter density) should those particles exist. In this situation, a photon enters the magnetic field region and converts into a chameleon particle. The windows on either side of the chamber would then act as totally reflecting mirrors to the chameleon particles. Over time those particles would convert back into photons which pass through the windows and strike our detector.
