Thursday, 13 May 2004 - h. 15:00 

Auditorium B. Touschek

  G. Cantatore
(INFN -Trieste)

Experimental study of the "vacuum element"
with PVLAS


Vacuum is the most abundant element in the Cosmos. The nature of vacuum as a material medium can be evidenced by studying its magneto-optical activity using high-sensitivity ellipsometry techniques. In particular, from a measurement of the macroscopic effects due to vacuum magnetic birefringence, it is possible to determine physical parameters relative to microscopic photon-photon interactions at low energy. Such processes include, among others, photon-photon scattering, predicted by QED but not yet experimentally confirmed, and the production of neutral, light, scalar/pseudoscalar particles coupled to two photons.
The PVLAS experiment, presently taking data at L.N.L., uses a 6 T superconducting dipole magnet to excite a pneumatic vacuum region, and a polarised laser beam as a probe of the vacuum structure when perturbed by the field. In addition, the optical path in the interaction region is amplified by means of a high-finesse Fabry-Perot optical resonator.
Relevant physical processes, along with their experimental signature, will be illustrated, together with the measurement technique employed by PVLAS. The most recent results obtained thus far will also be discussed. In particular, one observes an ellipticity signal compatible with a magnetic birefringence generated in the Fabry-Perot cavity.


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MCD, 22/4/2004