Session KL: Fundamental Symmetries III

Toward the Future: Upgrading the 6He-CRES Experiment with an Ion Trap

The ⁶He-CRES collaboration is developing the Cyclotron Radiation Emission Spectroscopy (CRES) technique to, for the first time, precisely measure the energy spectrum of βs over the range of a few MeV. The goal is to search for chirality-flipping interactions via the Fierz interference parameter, b_Fierz. The present apparatus works with noble neutral radioactive gases contained within a cylindrical volume, which also serves as an RF waveguide. Some sources of systematic uncertainty could be simplified by using a Penning trap to confine ions to the center of the decay volume. This combination of the CRES technique with ion trapping would add a powerful spectroscopic technique applicable to a wide variety of species at radioactive beam facilities. 

The introduction of ions to the system requires new components for ionization and separation of the beam, as well as a radio-frequency quadrupole trap (RFQ) to cool and bunch the beam for efficient transport and injection into the Penning trap. The upgrade would also require altering the current geometry and RF structure of the waveguides. I will cover an overview of experimental constraints and limits, then discuss their solutions and status of the ion trap addition to the ⁶He-CRES experiment.   

$^6$He-CRES: How to interpret the cyclotron radiation of betas in the $^6$He-CRES waveguide.

The $^6$He-CRES experiment at the University of Washington CENPA measures the $^6{\rm He}$ beta decay energy spectrum by measuring the cyclotron radiation of magnetically trapped betas in a waveguide. Radiation in the TE$_{11}$ mode propagates down the guide, coupling to low noise amplifiers. The output of the amplifiers is mixed down to frequencies below about a GHz and then a Fourier transform is performed and a spectrogram recorded. The resulting spectrogram contains high power bins forming tracks that increase in frequency over time. The slope of the tracks is determined by the total radiated power, which also includes coupling to higher harmonic modes outside of the observation bandwidth. In this talk I will discuss how an understanding of guide and cavity modes that betas can excite in our system allows for more accurate predictions of how slopes and observed power change with frequency, field, and position in the guide.   

Expanding RIB Capabilities at the Cyclotron Institute: 3He-LIG Production with an Isobar Separator, LSTAR

The primary goal of a new facility, TAMUTRAP, at the Cyclotron Institute, Texas A&M Univeristy, is to look for physics beyond the standard model by searching for a possible scalar currents contributing to the weak interaction. In particular, we will measure the β–ν correlation parameter, a_βν, in several β-delayed proton emitters initially confined in a novel and unique cylindrical Penning trap. This trap has been designed to be very large (180-mm inner diameter) so that β-delayed protons of up to 4.25 MeV energy are fully contained radially by the 7-T field of the magnet. As the proton-rich radioactive-ion beams (RIBs) needed for the TAMUTRAP program are developed at the Cyclotron Institute, we have commissioned the facility by demonstrating the ability to perform precise mass measurements using offline ion sources. Once RIB is successfully produced and transported to TAMUTRAP, we will be uniquely suited to observe the β-delayed proton decays of ^20,21Mg, ^24,25Si, ^28,29S, ^32,33 Ar and ^36,37Ca with 4π collection of the βs and delayed protons.

In order to produce the proton-rich RIBs for TamuTrap, a new production target and beamline is being constructed at the Cyclotron Institute. The high-intensity primary beam of ³He from the K150 cyclotron will impinge on a heavy target with the reaction products collected and extracted using the light-ion guide (LIG) technique. Following this we have designed LSTAR, a compact, high-resolution isobar separator to purify the RIBs in order to prevent overloading TAMUTRAP's RFQ cooler and buncher with contaminants.

An overview of the He-LIG and LSTAR systems and their expected performance will be presented, largely within the context of the TAMUTRAP science program.   

Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Measurements using different techniques are important for investigating whether there are unidentified systematic effects in any of the measurements. In this paper we report a new measurement using the Los Alamos asymmetric magneto- gravitational trap where the surviving neutrons are counted external to the trap using the fill and dump method.  The new measurement gives a free neutron lifetime of  t_n=877.1(2.6)_stat(0.8)_syst.  Although this measurement is not as precise, it is in statistical agreement with previous results using in situ counting in the same apparatus.

    

A Quantitative Measure of the Cleaning of Quasi-bound Neutrons in UCNtau

The UCNtau experiment, at Los Alamos National Lab, uses permanent magnets and gravity to trap polarized free ultracold neutrons (UCN's) for measuring the lifetime.  This value with neutron decay correlation coefficients can be used to probe beyond Standard Model physics and with the increased precisions now available can begin to be used to evaluate different theoretical approaches to beta decay corrections.  During part of the 2020 run cycle a vertical G10 copper coated plate was inserted in a buffer volume upstream of the trap to block all but the higher energy neutrons normally populating the experiment.  Data was taken with and without the usual cleaning of the highest energy quasi-bound neutrons which may kinematically escape the trap before decaying.  Comparing the resulting trap lifetimes gives a measure of cleaning efficacy by allowing an empirical bound to be placed on its efficiency.  Analysis and results will be presented.

    

Search for mirror neutrons at ORNL

The possibility that the neutron might transform into a sterile, mirror neutron has been proposed as a solution to questions such as the nature of dark matter and origin of the matter-antimatter asymmetry and has been linked to anomalies such as the neutron lifetime puzzle. We have conducted searches for neutrons transforming into mirror neutrons with a small mass difference using the Magnetism Reflectometer instrument at the Spallation Neutron Source. A first measurement has excluded the possibility that this phenomenon could explain the neutron lifetime anomaly. We will present improved limits from a second experimental search at the SNS with significantly reduced backgrounds and improved understanding of the neutron flux.