Session K03: Fundamental Symmetries with Neutrons

Symmetries and nonreciprocity: a light wave's perspective

Symmetries of crystals often give them fascinating and useful physical properties. It is especially true in the optical domain, where breaking or introducing symmetries can result in new qualitative phenomena. We will examine the effect of broken time reversal and spatial inversion symmetries in a medium on the propagation of light and find nonreciprocal absorption and refractive index in such situations. We will also see how such nonreciprocity can be enhanced in resonance with spin transitions and by artificial chiral structures.   

Neutron decay correlations (the alphabet soup)

In this talk, I want to give an overview about the measurement of decay correlations in neutron beta decay. I will describe how they are connected, and I will describe their motivation: Most prominent is the determination of the coupling constants of weak interaction, and consitency checks that allow for the search for Beyond-Standard-Model Physics.   

BL3: The Next Generation Neutron Lifetime Measurement Using the Beam Method

Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. A precise measurement of the neutron lifetime, along with neutron beta decay correlations, can provide tests of CKM unitarity and is needed for Big Bang Nucleosynthesis models of the primordial 4He abundance, which correlates with other cosmological parameters. A next generation beam method experiment, BL3 at the NCNR, aims to improve the systematic precision of neutron lifetime measurements in order to resolve the discrepancy between in-flight decay and trapped neutron measurements. In BL3, the recoil protons from neutron beta decay are born in a quasi-Penning trap with magnetic and electric fields which transport them to a segmented silicon detector. The BL3 experiment will use a larger beam with higher neutron flux, which requires a new and improved apparatus to reach an ultimate precision of <0.3 s. We will discuss simulations of proton transport and components of the new BL3 apparatus.   

Improvements to the neutron detector for the BL3 experiment

The goal of the BL3 Experiment is to measure the neutron in-flight decay lifetime with an absolute precision of 0.3 s. This is needed to resolve the discrepancy between previous in-flight decay measurements versus experiments using trapped UCNs. One source of systematic uncertainty arises from measuring the neutron fluence through the penning trap. To improve the neutron count measurement, a novel "caustic" aperture design can be used to provide perfect uniform detection efficiency across the entire beam profile. I will share analytic solutions for uniform detection efficiency in 2D and numerical methods for designing 3D apertures for circular detectors.   

Design of Modular NaI(Tl) Detectors for Fundamental Symmetry Measurements with Neutrons

The NOPTREX and Nab collaborations seek to utilize the fundamental nature of the neutron to probe the weak interaction. These experiments exemplify the variety of demands for different detection parameters, such as the gain or timing/energy resolution. In an effort to efficiently meet these various requirements using one set of detectors, we have developed an array of modular NaI(Tl) detectors with novel electronics that allow for operation in both current or pulse mode to accommodate better energy and timing resolution, respectively. To process the data from the detectors, we also have two independent data acquisition systems tailored to the demands of each experiment consisting of the CAEN DT5751 digitizer for the Nab timing measurements and the CAEN DT5560SE digitizer for the NOPTREX P- and T-Odd measurements. The development of this system has involved conducting experiments to determine the optimal design for the detectors, characterizing the detector components, and testing the data acquisition systems. The adaptability of NaI(Tl) scintillator crystals will allow for a wide range of uses for these detectors in nuclear physics experiments.   

He-3 Spin transport system at the nEDM@SNS experiment

The electric dipole moment (EDM) violates a fundamental symmetry of nature called charge parity (CP) conjugation, which is akin to reversing the arrow of time. Discovery of a nonzero EDM of an elementary particle would help to explain the predominance of matter over antimatter in the universe, even though both were generated in equal quantities during the Big Bang. The goal of the nEDM@SNS experiment at Oak Ridge National Laboratory is to improve the sensitivity to the neutron EDM by two orders of magnitude. This experiment will measure the precession frequency of free neutrons, using the polarized He-3 isotope as a co-magnetometer. In this talk, I will discuss the design of a system of magnetics used to transport polarized He-3 into the EDM measurement cell.