Physics beyond the Standard Model predicts the possible existence of new particles that can be searched at the low energy frontier in the sub-eV range. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles", such as axion or Axion-Like Particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of 2 × 14.3 m. In 2014, this experiment has been run with an outstanding sensitivity, using an 18.5 W continuous wave laser emitting in the green at the single wavelength of 532 nm. No regenerated photons have been detected after the wall, pushing the limits for the existence of axions and ALPs down to an unprecedented level for such a type of laboratory experiment. The di-photon couplings of possible pseudoscalar and scalar ALPs can be constrained in the nearly massless limit to be less than 3.5·10 −8 GeV −1 and 3.2·10 −8 GeV −1 , respectively, at 95% Confidence Level.

2 3 4 5 6 7 8 9 10 11 12 and experimental 13, , , 14 15 16 studies shed light on possible new physics beyond the standard model of particle physics, which can be probed with sub-eV energy experiments. They were triggered by the observation of the PVLAS collaboration 17 , newly disclaimed 18,19 , of a rotation of polarization for light propagating in the vacuum permeated by a transverse magnetic field. The OSQAR project 20 proposed to investigate such possibilities by reusing superconducting dipole prototypes and related infrastructure developed at CERN for the Large Hadron Collider (LHC). Combined with innovative optical techniques, unique opportunities in the emerging field of laser-based particle physics are being taken. Here we report first results from the OSQAR photon regeneration experiment. When submitted to a transverse magnetic field, properly polarized photons can couple to weakly interacting scalar or pseudo-scalar particles like axions undergoing quantum oscillations 21 in a similar way to neutrinos. If an optical barrier is introduced in the light path, only photons converted into scalars or pseudoscalars will not be absorbed and can be regenerated on the other side of the barrier, allowing their detection as "a shining light through a wall" 22 . For this, a LHC superconducting dipole providing a field of up to 9.5 T over 14.3 m was equipped with an optical barrier at centre. As a new way to amplify the photon-axion conversions, the magnet aperture was filled with nitrogen gas at a specific pressure. At one magnet end an 18 W Ar+ laser was installed and aligned with a CCD detector sitting on the opposite end. As a result, no regenerated photons were detected. New bounds for mass and coupling constant for purely laboratory experiments aiming to detect any hypothetical scalars and pseudo-scalars which can couple to photons were obtained at 95% confidence level.The axion is a neutral pseudo-scalar particle predicted independently by S. Weinberg 23 and F. Wilczek 24 from the Peccei and Quinn 25 symmetry breaking. It remains the most plausible solution to the strong-CP problem 26 , i.e. the answer to the following question: Why the CP symmetry (Charge and Parity conservation), in view of the negative measurement results of the neutron electric dipolar moment 27 , seems not to be broken by the strong interaction? Recently, it has also been emphasized that the axion constitutes a fundamental underlying feature of the string theory in which a great number of axions or Axion-Like Particles (ALPs) is naturally present 26 . In addition, the interest in axion search lies beyond particle physics since such hypothetical light spin-zero particles are considered as one of the most serious darkmatter candidates 28 , and the only non-supersymmetric one. Within this scope and in agreement with previous measurement results excluding heavy axions 29 , the allowed range for the axion mass is nominally 10 -6 < m A < 10 -2 eV. From the experimental point of view, the hunt for light axions can be classified in two compleme...

Various fundamental-physics experiments such as measurement of the birefringence of the vacuum, searches for ultralight dark matter (e.g., axions), and precision spectroscopy of complex systems (including exotic atoms containing antimatter constituents) are enabled by high-field magnets. We give an overview of current and future experiments and discuss the state-of-the-art DCand pulsed-magnet technologies and prospects for future developments. * Electronic address: budker@uni-mainz.de †