Shining a light on strangeness

The hyperon plays a key role for our understanding of the early universe, neutron stars, and the processes responsible for forming matter itself. The hyperon is a composite system of 3-quarks. The most familiar systems of 3-quarks are the nucleons - the protons and neutrons which make up atomic nuclei. A hyperon is essentially a nucleon in which one or more of its quarks is replaced by its heavier partner, the strange quark.

In atomic nuclei only nucleons exist with significant probabliity. However when studying systems at higher densities, pressures or temperatures, heavier strange quarks play an increasingly important role. Objects where hyperons are thought to be important include neutron stars. In heavy neutron stars, matter can be squashed up to ten times the density of a typical atomic nucleus. In these highly dense systems, hyperons constantly appear. Theories predict that heavy stars could have similar fractions of hyperons and nucleons. Therefore, fundamental properties of neutron stars, such as their mass, cooling mechanisms and stability heavily depend on the nature of the interaction between hyperons and nucleons. However, reliable information on the hyperon-nucleon interaction has been elusive for many decades. This fellowship will enable critical data on the hyperon-nucleon interaction to be obtained, utilising novel techniques and methods, which will improve our understanding of the properties and composition of neutron stars.

Hyperons also play a key role in the evolution of the universe. The early universe is thought to have initially existed in a plasma of free quarks and gluons, where the gluon is the messenger particle of the strong force which holds quarks together. As the universe cooled it went through an epoch where a gas of excited hyperons froze out of the plasma (when the universe was only microseconds old). Currently, our knowledge of the properties of these excited hyperons is poor. The programme will deliver much needed information to establish these states by producing them in the laboratory. This will constrain models of the early universe. The number and properties of the excited hyperons also constrains our basic understanding of the forces that hold quarks together. New theoretical advances have recently allowed the excited hyperons to be predicted from the theory of the strong force. We will provide important data to test these new advances, enhancing our current knowledge.

The research programme will use extremely intense beams of high-energy photons and large-particle detector systems. The experiments will take place at the Thomas Jefferson National Laboratory in the USA, one of the leading facilities in the world for such studies.