Search for strange matter by Rutherford backscattering

Abstract

According to a number of suggestions, stable strange matter could exist in the form of supermassive nuclei (or 'strange nuggets')^1,2. In contrast to ordinary nuclei, which contain only 'up' and 'down' quarks, a piece of strange matter should comprise a mixture of 'up', 'down' and 'strange' quarks in roughly equal proportions. Small amounts of strange matter could have survived from the early stages of the Universe¹. Alternatively, strange matter might reach the Earth as a flux of strange nuggets produced in collisions of neutron stars³. Limits to the cosmic flux of strange nuggets with masses in the range from 10⁻⁴ to 250 g have been obtained in a search for light produced by the nuggets in the upper atmosphere⁴. Here we report the results of a search for supermassive nuclei by using Rutherford backscattering of heavy ions. The method is sensitive to a broad range of masses extending to those that exceed the projectile mass by several orders of magnitude. Upper limits for the abundance of strange nuggets with masses A ≈ 4 × 10² to 10⁷ AMU relative to the number of nucleons were found to be in the range 10⁻¹⁰ to 10⁻¹⁴.