摘要
Our knowledge of the possible existence in nature of stable exotic particles depends solely upon experimental observation. Using a sensitive laser spectroscopy technique, we searched for a doubly charged particle accompanied by two electrons as an anomalously heavy isotope of helium in the Earth’s atmosphere. The concentration of noble-gas-like atoms in the atmosphere and the subsequent very large depletion of the light [Formula presented] isotopes allow stringent upper limits to be set on the abundance: [Formula presented] per atom in the solar system over the mass range of 20–10000 amu. © 2004 The American Physical Society.