First Results from the CERN Axion Solar Telescope

Abstract

Hypothetical axion-like particles with a two-photon interaction would be produced in the Sun by the Primakoff process. In a laboratory magnetic field ("axion helioscope") they would be transformed into X-rays with energies of a few keV. Using a decommissioned LHC test magnet, CAST ran for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling gaγ < 1.16 × 10 −10 GeV −1 at 95% CL for ma < ∼ 0.02 eV. This limit, assumption-free, is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment over a broad range of axion masses.

Search for 14.4 keV solar axions emitted in the M1-transition of57Fe nuclei with CAST

“…To examine how the Primakoff axion tail affects our result (28), we performed two additional χ 2 analysis of the experimental signal spectrum using as fit functions: i) N Fe + N P , and ii) N P . Here N Fe is given by equations (22) and (26), while N P corresponds to the expected spectrum of the Primakoff axion tail (19) multiplied by the axion-photon conversion probability (24) and the detection efficiency. The results of these fits are shown in table 2.…”

“…On the other side of the magnet, there is another MICROMEGAS detector covering one bore, and an X-ray mirror telescope with a pn-CCD chip as the focal plane detector at the other bore, both intended to detect photons produced from axions during the sunrise solar tracking. More details about the CAST experiment and detectors can be found in [18][19][20][21][47][48][49].…”

“…During the Phase I (2003)(2004) [19,20] the experiment operated with vacuum inside the magnet bores and the sensitivity was essentially limited to m a < 0.02 eV due to the coherence condition. In the second phase (so-called Phase II) which started in 2005, the magnet bores are filled with a buffer gas in order to extend the sensitivity to higher axion masses.…”

“…Such axions would have a continuous energy spectrum peaked near the mean energy of 4.2 keV and dying off above ∼10 keV. Most of the experiments that have been designed to search for these axions are based on the coherent axion-to-photon reconversion in a laboratory transverse magnetic field (the axion helioscope method [11][12][13][14][15][16][17][18][19][20][21]), or in the intense Coulomb field of nuclei in a crystal lattice of the detector (the Bragg scattering technique [22][23][24][25][26]). …”

GAUGE: the GrAnd Unification and Gravity Explorer

“…Experimental searches probe axions either through their coupling to photons (2 photon-axion vertex) or though the mass-spin interaction of (3). The former are typically resonant cavity searches such as ADMX [12], the CernAxion-Solar-Telescope (CAST) [13] or the PVLAS [14] search for vacuum birefringence. The latter search for axions through their mass-spin (or spinspin) interactions.…”