No light shining through a wall

We are the first to present here the results of a pulsed ”light shining through a wall” experiment, specifically designed to test the PVLAS claims. Our pulsed approach allows us to measure very small conversion rates free from the inevitable false counts of photon detectors. We have not detected any regenerated photons, testing conversion and back conversion on a total of more than 4× 10 incident photons. We can therefore invalidate the axion interpretation of the original PVLAS results, with a confidence level higher than 94 %. The axion was first proposed 30 years ago to solve the strong CP problem [1] and might be a major component of galactic dark matter [2]. Since it is very light and extremely weakly coupled to ordinary matter and to light, its search is a challenging experimental task [3]. Last year, the PVLAS collaboration announced a possible observation of axion-like particles [4] [5]. But the photonaxion coupling inferred from their measurements is inconsistent with previous experimental astrophysical constraints [3], so that it needs to be urgently confirmed by a purely laboratory-based experiment, as advocated by S. Lamoreaux [6]. Here we present the results of our photon-axion regeneration experiment, which disagree with the PVLAS measurements, invalidating the axion-like particle interpretation of their optical measurements with a confidence level higher than 94 %. We show the exclusion curves corresponding to our null result, compared to the PVLAS[4] measurements and to the limits from the BFRT reference experiment[7]. While the existence of an axion remains a plausible hypothesis, our results are a very important step in the understanding of this particle, and they only support a very weakly coupled axion, hence difficult to detect. Given its cosmological importance, the search is definitely worth the