RUI: The aCORN Experiment to Measure the Beta-Neutrino Asymmetry in Neutron Decay

Hamilton College, Clinton NY

Investigators

Abstract

The aCORN collaboration intends to measure the beta-neutrino asymmetry, 'a,' in neutron decay with a relative uncertainty of 1%. The decay of the free neutron provides a nearly ideal system where we could probe the limits of the Standard Model of the electro-weak interaction because the decay coefficients can be accurately calculated in the standard model. Some current tests of the self-consistency of the Standard Model are limited by the 4% experimental uncertainty in 'a.' The aCORN experiment relies on separating neutron decays into two classes; one in which the beta and neutron are emitted nearly parallel, and one in which they are nearly anti-parallel. A set of electric and magnetic fields guide the particles to detectors at opposite ends of a 3m long vacuum vessel. With this apparatus, the determination of 'a' is reduced to counting the numbers of protons in the two classes. The apparatus has been designed to reduce systematic errors below 0.5%. The experiment will begin its first physics run on neutron guide NG-6 at NIST in the spring of 2012, and will move to the new guide NG-C when it becomes available in 2013. Hamilton College will be involved in several aspects of the experiment throughout the operations phase. We will manage the distributed data analysis effort including both front end data reduction software at NIST and final analysis software distributed throughout the collaboration. We will continue to model magnetic and electric field geometries as inputs to a Monte Carlo simulation and as a way to improve the physical apparatus. Toward the end of the run we will implement an alignment check using electrons from a hot filament. We will also continue to maintain magnetic field alignment equipment including power supplies and a field mapping robot. Including undergraduates in research is a vital part of the culture at Hamilton College. We see research as crucial to attracting strong students to the sciences, producing scientifically knowledgeable graduates, and inspiring them to continue in science after they graduate. We have a history of including undergraduates in research, and about half of our research students go on to further education in physics or engineering. Furthermore, the nurturing environment at Hamilton is especially important for attracting women to physics. A quarter of the students that have come through our group are women, and six of these eight women have gone to graduate school in science or education. The proposed work will continue to involve significant numbers of undergraduates, both at Hamilton and at NIST. Our students can own a manageable piece of the project under close faculty mentoring Hamilton, and later integrate their piece into the final system in the environment of a national lab.