利用高純鍺探測器於國聖核電廠搜尋軸子

Abstract

In order to solve the strong CP problem, a new neutral particle with spin-parity 0^{-}, the axion, was invented. The strong CP problem is perplexing because it will manifest itself as an enormous neutron electric dipole moment: ten orders of magnitude larger than the experimental constraint. Although, from the experimental point of view, axion remains undiscovered, there is still strong interest in axions while other solutions to strong CP problem are not explicitly better. For instance, axions and weakly interacting massive particles (WIMPs) are two leading candidates for dark matter in our universe. A search for axions in specific nuclear transitions was performed at the Kuo-Sheng Nuclear Power Plant. Because of the pseudoscalar nature of axions, they could be emitted by competing with photons via nuclear de-excitation in reactor. Similar to neutrinos, axions interact feebly with normal matter, which makes the detection of such particles difficult. A 1.06 kg high-purity germanium detector was placed 28 meters from reactor core to detect single photons produced by axion Primakoff and/or Compton conversions inside the detector. For axion-to-photon branching ratio as well as axion coupling constants, two model-independent limits have been derived at 90% confidence level. Although the g_arr limit is not as competitive as other experiments, our limit on g_aee is unique.