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Measuring the Magnetic Birefringence of Vacuum: The Pvlas Experiment
International Journal of Modern Physics A, 2012
We describe the principle and the status of the PVLAS experiment which is presently running at the INFN section of Ferrara, Italy, to detect the magnetic birefringence of vacuum. This is related to the QED vacuum structure and can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Such an effect is predicted by the Euler–Heisenberg Lagrangian. The method is also sensitive to other hypothetical physical effects such as axion-like particles and in general to any fermion/boson millicharged particle. Here we report on the construction of our apparatus based on a high finesse (> 2·105) Fabry–Perot cavity and two 0.9 m long 2.5 T permanent dipole rotating magnets, and on the measurements performed on a scaled down test setup. With the test setup we have improved by about a factor 2 the limit on the parameter Ae describing nonlinear electrodynamic effects in vacuum: Ae < 2.9 · 10-21 T-2 @ 95% C.L.
Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment
New Journal of Physics, 2013
The PVLAS collaboration is presently assembling a new apparatus (at the INFN section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB is related to the structure of the quantum electrodynamics (QED) vacuum and is predicted by the Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Using the very same optical technique it is also possible to search for hypothetical low-mass particles interacting with two photons, such as axion-like (ALP) or millicharged particles. Here we report the results of a scaled-down test setup and describe the new PVLAS apparatus. This latter is in construction and is based on a highsensitivity ellipsometer with a high-finesse Fabry-Perot cavity (> 4 × 10 5) and two 0.8 m long 2.5 T rotating permanent dipole magnets. Measurements with the test setup have improved, by a factor 2, the previous upper bound on the parameter A e , which determines the strength of the nonlinear terms in the QED 4 Author to whom any correspondence should be addressed. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
The European Physical Journal C, 2016
Vacuum magnetic birefringence was predicted long time ago and is still lacking a direct experimental confirmation. Several experimental efforts are striving to reach this goal, and the sequence of results promises a success in the next few years. This measurement generally is accompanied by the search for hypothetical light particles that couple to two photons. The PVLAS experiment employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In this paper we report on the latest experimental results of this experiment. The data are analysed taking into account the intrinsic birefringence of the dielectric mirrors of the cavity. Besides a new limit on the vacuum magnetic birefringence, the measurements also allow the model-independent exclusion of new regions in the parameter space of axion-like and milli-charged particles. In particular, these last limits hold also for all types of neutrinos, resulting in a laboratory limit on their charge.
First results from the new PVLAS apparatus: A new limit on vacuum magnetic birefringence
Physical Review D, 2014
Several groups are carrying out experiments to observe and measure vacuum magnetic birefringence, predicted by Quantum Electrodynamics (QED). We have started running the new PVLAS apparatus installed in Ferrara, Italy, and have measured a noise floor value for the unitary field magnetic birefringence of vacuum ∆n (vac) u = (4 ± 20) × 10 −23 T −2 (the error represents a 1σ deviation). This measurement is compatible with zero and hence represents a new limit on vacuum magnetic birefringence deriving from non linear electrodynamics. This result reduces to a factor 50 the gap to be overcome to measure for the first time the value of ∆n (vac,QED) u predicted by QED: ∆n (vac,QED) u = 4 × 10 −24 T −2. These birefringence measurements also yield improved modelindependent bounds on the coupling constant of axion-like particles to two photons, for masses greater than 1 meV, along with a factor two improvement of the fractional charge limit on millicharged particles (fermions and scalars), including neutrinos.
Feasibility study of an experiment to measure the vacuum magnetic birefringence
Czechoslovak Journal of Physics, 2005
The use of a recently decommissioned 15-meters long twin aperture LHC supercon-ducting magnet prototype having a transverse magnetic fieldB ≈ 9.5 T provides the unique opportunity for the construction of a new powerful experiment to measure the Vacuum Magnetic Birefringence (VMB). The values or the limit values of the mass and of the coupling constant to two photons of possible dark matter candidates such as axions are aimed to be deduced from such an experiment. In this article, the technical feasibility study of a new setup to measure the VMB will be presented. It is based on a linear optical resonant cavity house in the LHC superconducting dipole prototype. The mechanical integrations of the optical components inside the magnet aperture as well as the optical detection principles will be presented. A comparison of the expected performances with respect to the present reference results for this type of experiment will also be given.
Letter of Intent to measure Vacuum Magnetic Birefringence: the VMB@CERN experiment
2018
Non linear electrodynamic effects have been predicted since the formulation of the Euler effective Lagrangian in 1935. These include processes such as light-by-light scattering, Delbrück scattering, g-2 and vacuum magnetic birefringence. This last effect deriving from quantum fluctuations appears at a macroscopic level. Although experimental efforts have been active for about 40 years (having begun at CERN in 1978) a direct laboratory observation of vacuum magnetic birefringence is still lacking: the predicted magnetic birefringence of vacuum is ∆n = 4.0 × 10 −24 @ 1 T. Key ingredients of a polarimeter for detecting such a small birefringence are a long optical path within an intense magnetic field and a time dependent effect. To lengthen the optical path a Fabry-Perot interferometer is generally used. Interestingly, there is a difficulty in reaching the predicted shot noise limit of such polarimeters. The cavity mirrors generate a birefringence-dominated noise whose ellipticity is amplified by the cavity itself limiting the maximum finesse which can be used. This Letter of Intent proposes an experiment which overcomes this difficulty by using a LHC superconducting magnet together with a novel polarisation modulation scheme for the polarimeter. The proposing authors all come from previous experimental efforts to measure vacuum magnetic birefringence and represent the maximum expertise in the field. Using the proposed setup, vacuum magnetic birefringence should be detected with an SNR = 1 in less than 1 day.
2005
The use of a recently decommissioned 15-meters long twin aperture LHC superconducting magnet prototype having a transverse magnetic field B ~ 9.5 T provides the unique opportunity for the construction of a new powerful experiment to measure the Vacuum Magnetic Birefringence (VMB). The values or the limit values of the mass and of the coupling constant to two photons of possible dark matter candidates such as axions are aimed to be deduced from such an experiment. In this article, the technical feasibility study of a new setup to measure the VMB will be presented. It is based on a linear optical resonant cavity housed in the LHC superconducting dipole prototype. The mechanical integrations of the optical components inside the magnet aperture as well as the optical detection principles will be presented. A comparison of the expected performances with respect to the present reference results for this type of experiment will also be given.
PVLAS : probing vacuum with polarized light
Nuclear Physics B - Proceedings Supplements, 2007
The PVLAS experiment operates an ellipsometer which embraces a superconducting dipole magnet and can measure ellipticity and rotation induced by the magnetic field onto linearly polarized laser light. The sensitivity of the instrument is about 10 -7 rad Hz -1/2 . With a residual pressure less than 10 -7 mbar the apparatus gives both ellipticity and rotation signals at the 10-7rad level with more than 8 sigma sob ratio in runs that last about 1000 sec. These signals can be interpreted as being generated largely by vacuum ellipticity and dichroism induced by the transverse magnetic field. If this interpretation is correct, a tool has become available to characterize physical properties of vacuum as if it were an ordinary transparent medium. A microscopic effect responsible for this induced dichroism could be the existence of ultralight spin zero bosons with mass of the order of 10 -3 eV, that would couple to two photons and would be created in the experiment by interactions of photons of the laser beam with virtual photons of the magnetic field. The inverse of the coupling constant to two photons would correspond to a mass M of the order of 10 6 GeV.