Symmetry Tests and Standard Model Backgrounds

The name Ernest Henley to me is inexorably linked with the idea of symmetry tests. Indeed I learned my first information about parity violation in nuclei from his classic work on time reversal and parity[1] and it was reading this paper which eventually led to my interest in and work in this field. Of course, it is not just Prof. Henley who has long been interested in the subject of invariance. Indeed, mankind has from the earliest days been fascinated with the concept of symmetry. The Pythagorans considered the circle and sphere to be the most perfect of two and three dimensional objects respectively because of their obvious radial symmetry. The planets were assumed to move in precise circular orbits and the stars were assumed to be situated in the heavenly spheres. It is during recent decades that symmetry studies in physics have had a rebirth, however. The reason for this has to do with the development of modern physics. As long as physics was focussed on its classical roots of mechanics and electrodynamics, for which the exact laws of motion were known, the use of symmetry methods was, strictly speaking, not necessary. Indeed most books on classical mechanics written during the early part of the present century do not even mention the conservation of angular momentum—they just solve the Kepler problem exactly.[2] However, with the advent of particle and nuclear physics, wherein the underlying interactions and equations of motion are complex and unknown, the use