During 2014 the PVLAS experiment has started data taking with a new apparatus
installed at the INFN Section of Ferrara, Italy. The main target of the
experiment is the observation of magnetic birefringence of vacuum. According to
QED, the ellipticity generated by the magnetic birefringence of vacuum in the
experimental apparatus is expected to be ψ(QED)≈5×10−11. No ellipticity signal is present so far with a noise floor
ψ(noise)≈2.5×10−9 after 210 hours of data taking.
The resulting ellipticity limit provides the best model independent upper limit
on the coupling of axions to γγ for axion masses above 10−3eV