RUI: Precision Weak Interaction Studies in Nuclei

Wittenberg University, Springfield OH

Investigators

Abstract

The research supported by this award will probe the limits of our understanding of the weak interaction, one of the four fundamental forces of nature. Among other things, the weak interaction is responsible for the type of radioactive decay called beta decay in which a nucleus is transformed into a different nucleus with the emission of an electron and a neutrino. The award will allow the two scientists to carry out experiments in which they precisely measure the energy of electrons emitted in four different nuclear beta decays. Three of these experiments will test key aspects of the Standard Model of the electroweak interaction, which is the theory that describes the unification of two of the fundamental forces, the weak interaction and the electromagnetic interaction. These precision beta decay measurements are complementary to particle collider experiments in the search for new physics. A fourth proposed experiment aims to resolve uncertainties in the beta decay of potassium-40, an important tool in geochronology. The research program has the further goal and benefit of training highly talented undergraduate physics students. Students involved will gain experience with state-of-the-art software and experimental techniques, and will learn to think independently and gain a variety of practical problem solving skills. The broader impact is felt when these students enter the workforce in STEM fields or in teaching. The research program consists of several experiments involving the high precision measurement of the shapes of beta spectra. In two of the proposed experiments the goal is to provide a strong test of the Conserved Vector Current hypothesis in the electroweak sector of the Standard Model of particle physics. In a third experiment, the goal is to improve limits on non-Standard-Model contributions (Fierz terms) to the description of the weak interaction. A fourth experiment has the goal of resolving an uncertainty in the potassium-40 beta spectrum, which is relevant to applications in geochronology. Specifically, the carbon-14 beta spectrum will be measured using a new magnetic spectrometer at the University of Wisconsin-Madison. This spectrometer will be nearly identical in form to the superconducting spectrometer used to make the same measurement in oxygen-14, enabling reduced uncertainties arising from higher order matrix element contributions. Measurements in fluorine-20 and helium-6 will be carried out at the National Superconducting Cyclotron Laboratory using implantation into a scintillator detector, which will have significantly different systematic effects from the magnetic spectrometer measurements and will be important in achieving low thresholds. A fourth experiment has the goal of measuring the shape of the potassium-40 beta spectrum. Knowledge of this spectrum shape is important for a standard technique in radioactive dating of geologic samples, but a recent report suggests the shape may not be as well understood as had been thought. An important aspect of all these measurements is in assessing and correcting for systematic effects through measurement and computational modeling.