2008 Chadwick medal and prize

Professor Keith Green and Professor J Michael Pendlebury

Rutherford Appleton Laboratory / University of Sussex

For their outstanding contributions to the measurement of the neutron electric dipole moment, and of other fundamental properties of the neutron.

The Chadwick medal and prize for distinguished research in particle physics has been awarded to Professor J Michael Pendlebury, Research Professor at the University of Sussex and Professor Keith Green, Senior Research Fellow at the University of Sussex and Honorary Scientist at the Rutherford Appleton Laboratory, for their outstanding contributions to the measurement of the neutron electric dipole moment, and of other fundamental properties of the neutron.

One of the outstanding mysteries of cosmology is why there is so much more matter than antimatter in the Universe. The key explanation depends on subtle differences in the properties and behaviour of fundamental particles and their antimatter partners - so-called C, P and T symmetry violation - as predicted by particle-physics theories. The existence of a slight separation of positive and negative electric charges - a permanent electric dipole moment (EDM) - in the neutron would violate T and P symmetries. Pinning down this elusive property would not only shed light on the processes in the early Universe that led to the dominance of matter, but also constrain theoretical models such as supersymmetry which aim to provide a deeper understanding of Nature. Different versions of supersymmetry predict different EDM values.

For more than 30 years, Pendelbury and Green have been organising and carrying out a series of exquisite experiments at the Institut Laue Langevin to measure the neutron EDM with ever-increasing sensitivity. They involve storing ultracold neutrons and making subtle magnetic measurements in an electric field. They are some of the most sensitive measurements that it is possible to make in physics. Recent work using novel equipment has substantially increased the sensitivity, leading to an EDM value considerably less than that predicted by many models.

Pendlebury and Green are playing leading roles in the development of the next-generation experiment expected to lead to a more than ten-fold increase in sensitivity, thereby adding further to the understanding of the fundamental nature of matter.