Nuclear Physics with Short-Lived Beams

In nuclear physics, processes involving beams of short-lived particles are difficult to study. By using a well-understood process, such as the photoproduction of the short-lived particle, we can resolve this problem. The major difficulty lies in determining the luminosity of our measurement. The traditional method of calculating a cross section requires knowledge of the numbers of both the beam and target particles. We cannot count our beam particles directly, but we can use previous cross section measurements to estimate our beam flux. Using relativistic kinematics, we can express the beam flux in terms of our short-lived particle’s energy and lab angle. The target length, typically used in these calculations, is only valid if the beam particle is traveling along the target axis. The effective number of target particles can be determined by comparing the kinematics of our short-lived beam with the geometrical properties of the target. By multiplying the numbers of beam and target particles thus obtained to get the luminosity, we can normalize the cross section. This talk will describe the development of this new technique and discuss several applications for which it is successfully being employed.