Experimental Search for Solar Axions via Coherent Primakoff Conversion in a Germanium Spectrometer

Abstract

Results are reported of an experimental search for the unique, rapidly varying temporal pattern of solar axions coherently converting into photons via the Primakoff effect in a single crystal germanium detector when axions are incident at a Bragg angle with a crystalline plane. The analysis of 1.94 kg yr of data from the 1 kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound by an axion-photon coupling of g agg , 2.7 3 10 29 GeV 21 , independent of axion mass up to ϳ1 keV. [S0031-9007(98)07812-0] PACS numbers: 14.80. Mz, 96.60.Vg Early QCD theories predicted a particle with the quantum numbers of the h meson, but with a mass close to that of the pion. A term added to the QCD Lagrangian to ameliorate this so-called U(1) problem violated CP invariance in strong interactions and implied a neutron electric-dipole moment about 10 9 times larger than the experimental upper bound [1]. Peccei and Quinn [2] introduced a new field causing strong CP violation to vanish dynamically. Subsequently, Weinberg [3,4] and Wilczek [5] demonstrated that the Peccei-Quinn mechanism generates a Nambu-Goldstone boson, the axion, that couples to a two-photon vertex via a coupling g agg . Axion production via the Primakoff effect occurs when a photon couples to a charge via a virtual photon, producing an axion. Detection can occur by observing photons resulting from axions coupling to electrical charges via virtual photons.The dense volume of photons and charges in the sun or any star produces conditions for axion production. The Ge detector then can act as the axion-photon converter and detector. When the characteristic wavelength of the axion satisfies a Bragg condition in the single crystal Ge detector, photon production would occur with an expected temporal pattern depending on the changing relative directions between the vectors from the solar core and the crystalline planes.Extensive reviews of axion phenomenology and their effects on stellar evolution have been given by Raffelt [6,7] who gives a bound of 10 210 GeV 21 on the coupling of axions to the two-photon vertex from the population of red giant stars. A detailed treatment of solar axions and of a proposed method of detecting them was given by van Bibber et al. [8]. Details of a theory for searching for axions with germanium detectors were recently given by Creswick et al. [9]. The objective is to detect solar axions through their coherent Primakoff conversion into photons in the lattice of a germanium crystal when the incident angle satisfies the Bragg condition. The detection rates in various energy windows are correlated with the relative orientations of the detector and the sun [9]. This correlation results in a distinctive, unique signature of the axion. In this Letter, the results of a search using a 1 kg, ultralow background germanium detector installed in the HIPARSA iron mine in Sierra Grande, Argentina, at 410 24 00 S and 65 ± 22 0 W are presented. A description of the experimental setup and detector spectrum was given earlier by Di Gregori...

Particle dark matter and solar axion searches with a small germanium detector at the Canfranc Underground Laboratory

“…The limit presented here is practically equal to that obtained by the SO-LAX Collaboration with another Ge detector [20]. These limits are the mass independent (although solar model dependent) most stringent laboratory bounds for the axion-photon coupling obtained so far.…”

Search for axions from the Kuo-Sheng nuclear power reactor with a high-purity germanium detector

“…The KS limits on g aγγ are not as sensitive as those of CAST [25] and the solar-germanium [24] experiments for m a 10 4 eV at all branching ratios. On the contrary, the g aee sensitivities exceed those of the positronium decay [27] and macroscopic force [28] experiments.…”

“…The sensitivities are suppressed at "Decay" for the large (m a , g aγγ /g aee ) regions, , while region labeled "R" are from previous reactor axion experiments studying Γγγ [10]. Results from the other axion experiments using different techniques [23,24,25,26,29] are displayed as colored blocks. The astrophysical bounds [9] are denoted by the striped region.…”

“…At large m a 10 6 eV, the sensitivities in both g aγγ and g aee are dominated by the accelerator-based "beam dump" experiments [23]. Exclusion boundaries at small m a are defined by: (a) for g aγγ − the germanium [24] and CAST [25] experiments studying solar axions, and the axion dark matter searches with microwave cavity [26]; and (b) for g aee − the positronium decay [27] and macroscopic force [28] experiments. At g aγγ > 10 −2 GeV −1 , the solar axion experiments are limited by axion interactions inside the Sun [9].…”

Phenomenological constraints on axion models of dynamical dark matter

“…These include helioscope experiments such as CAST [38] and "light-shining-through-walls" (LSW) experiments such as BEV, GammaeV, and ALPS. Searches for coherent conversion of solar axions to X-ray photons in germanium and sodiumiodide crystals via Bragg diffraction which have been performed at experiments such as DAMA [39], TEXONO [40], SOLAX [41], and COSME [42] also fall into this category. The characteristic which distinguishes experiments in this class from others is that these experiments are affected by decoherence phenomena.…”