Results from the PVLAS attempt to measure vacuum magnetic birefringence and future outlook

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• Guido Zavattini (Ferrara INFN)
• Wednesday 23 June 2021, 13:30-14:30
• Zoom.

If you have a question about this talk, please contact Prof Ian Kenyon.

Sensitive magneto-optical polarimetry was proposed in 1979 as a means to detect vacuum electrodynamic non linearity, in particular Vacuum Magnetic Birefringence (VMB). This process is predicted in QED via the fluctuation of electron-positron virtual pairs but can also be due to hypothetical Axion Like Particles (ALPs). Today ALPs are considered a strong candidate for Dark Matter. Starting in 1992 the PVLAS collaboration, financed by INFN , Italy, attempted to measure VMB with a polarimeter based on an optical cavity permeated by a time dependent magnetic field and heterodyne detection. Two setups followed differing basically in the magnet: the first using a rotating superconducting 5.5 T dipole magnet and the second using two rotating permanent 2.5 T dipole magnets. At present PVLAS is the experiment which has set the best limit in VMB reaching a noise floor within a factor 10 of the predicted QED signal of ∆n(QED) = 2.5e-23 @ 2.5 T.  It was also shown that the noise floor was due to the optical cavity and a larger magnet is the only solution to increase the signal to noise ratio. The PVLAS experiment ended at the end of 2018. A new effort, VMB @CERN, which plans to use a spare LHC dipole magnet at CERN with a new modified optical scheme is now being proposed and tested. In this seminar a description of the PVLAS effort and the comprehension of its limits leading to a VMB @CERN will be given.

This talk is part of the Particle Physics Seminars series.

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