Experimental validation of a high accuracy test of the equivalence principle with the small satellite "Galileo galilet"

The small satellite "Galileo Galilei" (GG) has been designed to test the equivalence principle (EP) to 10(-17) with a total mass at launch of 250 kg. The key instrument is a di. fferential accelerometer made up of weakly coupled coaxial, concentric test cylinders rapidly spinning around the symmetry axis and sensitive in the plane perpendicular to it, lying at a small inclination from the orbit plane. The whole spacecraft spins around the same symmetry axis so as to be passively stabilized. The test masses are large (10 kg each, to reduce thermal noise), their coupling is very weak (for high sensitivity to differential effects), and rotation is fast (for high frequency modulation of the signal). A 1g version of the accelerometer ("Galileo Galilei on the Ground"-GGG) has been built to the full scale-except for coupling, which cannot be as weak as in the absence of weight, and a motor to maintain rotation (not needed in space due to angular momentum conservation). GGG has proved: (i) high Q; (ii) auto-centering and long term stability; (iii) a sensitivity to EP testing which is close to the target sensitivity of the GG experiment provided that the physical properties of the experiment in space are going to be fully exploited

Particle laser production at PVLAS: recent developments

In the PVLAS apparatus a polarised laser beam is used to probe the structure of quantum vacuum when it is perturbed by an external magnetic field. The photon-photon scattering process, taking place in the field region, could result in the production of light scalar/pseudoscalar particles coupled to two photons thought to be dark matter candidates. The photon-photon scattering induces a change in the polarisation state of the laser beam, and can be detected by optical techniques. The PVLAS collaboration has been operating the apparatus for about two years, and the available sets of data show the presence of a signal believed to originate within the magnetic field region. Preliminary results from the data sets will be presented, along with a brief discussion

A precise measurement of the Cotton-Mouton effect in neon

In this Letter, we report a novel measurement of the magnetically induced birefringence (Cotton–Mouton effect) in neon. Using a highly sensitive apparatus we were able to precisely measure the specific birefringence value of \Delta\nu = (5.9 ± 0.2)x10^-16 at the wavelength of 1064 nm (for B = 1 T and atmospheric pressure) and T 290 K. The results reported here are in agreement with theory, while the only previous precise measurement differs significantly

PVLAS results on laser production of axion-like dark matter candidate particles

Microscopic processes in the quantum vacuum, such as photon-photon scattering and the Primakoff effect, where light, neutral, scalar/pseudoscalar particles are produced from a two-photon vertex, could give rise, in the presence of an external magnetic field, to macroscopically observable optical phenomena, such as vacuum birefringence and dichroism. Such particles are candidate constituents of the Cold Dark Matter. The PVLAS collaboration is operating a high-sensitivity (similar to 10(-7) 1/root Hz) optical ellipsometer capable of detecting very small changes in the light polarisation state induced by a strong transverse magnetic field on a linearly polarised laser beam. This ellipsometer is capable of measuring vacuum birefringences and dichroisms, in an independent way, down to levels below 10(-8) rad, for about one hour of data taking time. Preliminary results, involving the observation of candidate signals in vacuum, will be discussed

Editorial note to: Experimental observation of optical rotation generated in vacuum by a magnetic field (Physical Review Letters (2006) 96 (110406))

The observed vacuum optical rotation signal reported in [1] has now been excluded by more recent results from the PVLAS Collaboration [2], which show that it was due to an instrumental artifact and was not of physical origin. These new data therefore also exclude the possible interpretation of the signal reported in [1], as caused by the existence of a light, neutral, spin-zero particle. [1] E. Zavattini et al., Phys. Rev. Lett. 96, 110406 (2006). [2] E. Zavattini et al., arXiv:0706.3419

Data acquisition and signal processing in the PVLAS experiment

Photonic crystals are commonly used in quantum electronics to generate harmonic or subharmonic beams from primary laser. One surprising result of quantum field theory is that vacuum behaves like a photonic crystal with a very weak nonlinearity. The virtual particle pairs associated to quantum fluctuations of charged fields, can be polarized by an external field and vacuum can thus become birefringent: the PVLAS experiment was originally meant to explore this strange quantum regime with optical methods. Since its inception PVLAS has found a new, additional goal: in fact vacuum can become a dichroic medium if we assume that it is filled with light neutral particles that couple to two photons, and thus PVLAS can search for exotic particles as well. PVLAS implements a complex signal processing scheme with some unusual features, the most outstanding being the uneven time spacing of the samples. Here we describe the double data acquisition chain and the data analysis methods used to process the experimental data

First run of the PVLAS experiment: Dark matter candidates production and detection

The PVLAS experiment is designed to study photon-photon interactions in the low energy region using optical techniques. In the PVLAS apparatus photons from a laser beam interact in vacuum with an external magnetic field, and the two-photon interaction results in the possible production of neutral, nearly massless, scalar/pseudoscalar particles. Evidence of particle production is extracted from the study of the light polarisation state after traversing a region where a the magnetic field is provided by a superconducting dipole magnet. Polarisation measurements are conducted using a very sensitive ellipsometer based on a high finesse (~100000), 6.4 m long, Fabry-Perot optical resonator. The PVLAS apparatus is now fully integrated and operational: the first commissioning run with a 4.0 T field has been successfully completed, the first data taking runs have been conducted, yielding a total integration time of about 20 hours, and data analysis is now in progress. We will present details from the commissioning run and preliminary results from the data runs