Search for anomalously heavy nuclei in gold and iron

Abstract

There are a number of theoretical motivations for searching for anomalously heavy isotopes ${}_{Z}X$ of known elements, where Z is the nuclear charge of the anomalous nucleus X. Such nuclei could arise from the binding of a new strongly interacting massive particle (SIMP) to the nucleus of a known element, and could thus be detected as an anomalously heavy isotope of that element. SIMPs have been proposed as candidates for dark matter, and for the lightest supersymmetric particle, as well as a possible explanation for ultra high-energy cosmic rays. A search for anomalous nuclei X has been performed by analyzing several unique samples including gold nuggets collected in Australia, Arizona and North Carolina, gold foils flown on NASA's LDEF satellite, and an Fe meteorite. In each gold sample we scanned for Au isotopes with masses up to $1.67 \mathrm{TeV}{/c}^{2}$ using PRIME Lab, the Purdue accelerator mass spectrometer facility. We have also searched for anomalous Fe isotopes with masses up to $0.65 \mathrm{TeV}{/c}^{2}$ in the iron meteorite sample. We find no evidence for SIMPs in any of our samples, and our results set stringent limits on the abundance of anomalous isotopes of ordinary matter as a function of X mass.