Polarized Ultra Cold Neutrons for Fundamental Symmetry Study

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

The universe displays several very fundamental symmetries with major consequences. Three of these are very familiar: that the origin in space of an experiment doesn't matter gives rise to momentum conservation; that the orientation in space doesn't matter gives rise to angular momentum conservation; that the time you start an experiment doesn't matter gives rise to energy conservation. These are known as 'continuous' symmetries. Less familiar are the 'discrete' symmetries. The most familiar ones are: (P) looking at the universe through a mirror; (C) changing all matter to anti-matter (and vice-versa); and (T) running the clock backwards. These are known to not be 'exact', but the combination of all three 'CPT' is at the foundation of all our theories. That the combination of 'CP' is violated is necessary to explain the origin of the small asymmetry which gives rise to our matter dominated universe. The cleanest way to study such fundamental symmetries is with simple well-understood systems. The neutron is a prime example. By measuring correlations in its beta decay properties we can probe fine details of its symmetry violation as well as several other important physics questions. Using ultra-cold neutrons makes these measurements very clean, and this grant supports one of the technologies required to make such experiments possible: the transport of ultra-cold neutrons from their production area to the experimental area and subsequent storage. Specialized coatings are required for this, and both evaporation (such as Ni-58) and laser deposition (of diamond films) have been developed with excellent results. The program is to improve the capabilities (such as with multi-layer films) and to integrate the technology into fundamental physics studies. These coatings are already being used in the UCN-A experiment at the Los Alamos National Laboratory, and several other groups are interested in using them as well. The techniques necessary to produce high-quality coatings include precision surface preparation, careful environment control, and comprehensive diagnostics. This provides an excellent training venue for students and new researchers, and couples them directly into critical roles for physics research both from a technology viewpoint, and as part of larger collaborative efforts to probe for new physics. In addition, these techniques find application in a variety of industrial processes, where successful coatings require very specialized skills and hand-on experience. For example, diamond coatings can significantly prolong the life of quartz process systems, can improve environment resistance of micro strain gauges, and provide harder surfaces for knife-edges. In accelerator systems, coatings play a significant role in ion source efficiencies and the holding time of polarized target cells.