Around the 2025 September Equinox, hundreds of experimental and theoretical particle physicists plan to gather in the Canary Islands for the 20th Patras Workshop on axions and other candidate particles for the dark matter that dominates the large-scale structure and dynamics of galaxies, galaxy clusters, and the universe itself. Twenty years ago, though, at the first such meeting, held in early December 2005 at the CERN physics laboratory near Geneva, Switzerland, Giovanni Cantatore from the University of Trieste and the Italian National Nuclear Physics Institute in Legnaro spoke on behalf of the PVLAS (Polarization of Vacuum with LASer) collaboration about the team’s observation of a signal consistent with the production of axions in the laboratory. “We have consistently observed a dichroism signal generated by a 1.1 m long, 5.5 T magnet,” Cantatore explained. “The beam (at wavelength 1064 nm) traverses the magnetic region about 50000 times.”
The image above shows the 1.3 mm beam waist of the laser within the high finesse infrared cavity at the PVLAS experiment in 2005. In 2007 the team swapped out their Lightwave Electronics 100 mW infrared laser for an Innolight 800 mW infrared laser with nine times smaller beam waist. The result was a nine-fold drop in the axion production signal into the “noise floor” of the exquisitely precise experiment. “The new observations do not show the presence of a rotation signal down to the levels of 18 nanoradians at 5 T (at 99% confidence level) with 45000 passes in the magnetic zone,” the PVLAS collaboration reported in a 2008 publication in the prestigious particle physics journal Physical Review D published by the American Physical Society.
Science Synergy Science Chair Dr. Noah Bray-Ali submitted an abstract to the 20th Patras Workshop describing the April 2021 theoretical prediction and April 2024 experimental confirmation of the rest-mass energy of the axion by Science Synergy (See Dark Matter Rest-Mass Energy Found to 44 ppm with Infrared). Using the experimentally observed value for the axion rest-mass energy together with the corresponding theoretical prediction for the strength of the coupling between the axion and a pair of photons, Bray-Ali calculated the size of the “dichroism” signal during the 2005 run of the PVLAS experiment with the large beam waist: The result is 170 nanoradians which is in rough agreement with the experimental result reported in a 2006 Physical Review Letter by the PVLAS team. The calculation also predicts that the signal — which results from the production of axion dark matter particles by the coupling of the infrared electric field of photons in the laser beam and the static magnetic field of virtual photons in the magnet — scales linearly with the beam waist of the laser within the high finesse infrared cavity inside the magnet: The predicted signal for the 2007 PVLAS run with the nine times smaller beam waist lands at 18 nanoradians which is right at the noise floor of the PVLAS experiment (signal-to-noise ratio of three-to-one).