New PVLAS results and limits on magnetically induced optical rotation and ellipticity in vacuum

TL;DR

The study re-evaluates magnetically induced effects in vacuum with upgraded PVLAS instrumentation, performing 2.3 T and 5 T vacuum runs to test for instrumental artifacts. Using a high-finesse Fabry-Perot cavity and a rotating 5 T magnet, the team isolates potential artifacts and finds no evidence for vacuum birefringence or dichroism within the stated limits, attributing the previously reported rotation signal to instrumental effects. The new results set stringent bounds on rotation and ellipticity, constrain the photon-photon cross-section to $\sigma_{\gamma\gamma} < 4.5\times10^{-34}$ barn, and exclude spin-zero boson interpretations compatible with earlier PVLAS reports, while mapping excluded regions in the mass–coupling parameter space. These findings significantly tighten constraints on new physics and clarify the experimental origin of past PVLAS signals.

Abstract

IIn 2006 the PVLAS collaboration reported the observation of an optical rotation generated in vacuum by a magnetic field. To further check against possible instrumental artifacts several upgrades to the PVLAS apparatus have been made during the last year. Two data taking runs, at the wavelength of 1064 nm, have been performed in the new configuration with magnetic field strengths of 2.3 T and 5 T. The 2.3 T field value was chosen in order to avoid stray fields. The new observations do not show the presence of a rotation signal down to the levels of $1.2\cdot 10^{-8}$ rad at 5 T and $1.0\cdot 10^{-8}$ rad at 2.3 T (at 95% c.l.) with 45000 passes in the magnetic field zone. In the same conditions no ellipticity signal was detected down to $1.4\cdot 10^{-8}$ at 2.3 T (at 95% c.l.), whereas at 5 T a signal is still present. The physical nature of this ellipticity as due to an effect depending on $B^2$ can be excluded by the measurement at 2.3 T. These new results completely exclude the previously published magnetically induced vacuum dichroism results, indicating that they were instrumental artifacts. These new results therefore also exclude the particle interpretation of the previous PVLAS results as due to a spin zero boson. The background ellipticity at 2.3 T can be used to determine a new limit on the total photon-photon scattering cross section of $σ_{γγ} < 4.5 \cdot10^{-34}$ barn at 95% c.l..

Figures (7)

• Figure 1: Schematic layout of the PVLAS apparatus. See text for description.
• Figure 2: Polar plot for the ellipticity signal generated with a 2.3 T magnetic field intensity when Helium gas is present in the vacuum chamber. The figure shows the signal for four different gas pressures: 5, 10, 15 and 20 mbar. Each data point represents amplitude and phase of the signal peak observed in a 100 s long time record. For these data, an ellipticity amplitude of $10^{-6}$ corresponds to a birefringence $\Delta n\approx10^{-17}$
• Figure 3: Summary table of typical spectra observed in vacuum in the measurements reported here. Each spectrum corresponds to about 600 s of data acquisition time (see text).
• Figure 4: QWP0 and QWP90 noise distributions in the magnet rotation frequency band $1.92\Omega_{Mag}$ -- $2.08\Omega_{Mag}$ for the 2.3 T rotation measurements. The vertical line indicates the resulting amplitude at $2\Omega_{Mag}$ determined from a weighted average of 100 s long data subsets. The value of $\sigma$ for the two configurations is also shown (see text).
• Figure 5: QWP0 and QWP90 noise distributions in the magnet rotation frequency band $1.92\Omega_{Mag}$ -- $2.08\Omega_{Mag}$ for the 5 T rotation measurements. The vertical line indicates the resulting amplitude at $2\Omega_{Mag}$ determined from a weighted average of 100 s long data subsets. The value of $\sigma$ for the two configurations is also shown (see text).