Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session FJ: Mini-symposium on Physics of Ultracold Neutron Sources IIMini-Symposium
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Chair: Jeff Martin, University of Winnipeg Room: Junior Ballroom A |
Friday, October 14, 2016 4:00PM - 4:12PM |
FJ.00001: Overview of Fierz Interference Analysis from UCNA Experiment Xuan Sun A non-zero Fierz interference term, the $b$ coefficient in the expansion of the beta decay rate in the Standard Model, can signify contributions to scalar and tensor interactions from physics beyond the Standard Model. In practice, $b \neq 0$ causes shifts in the shape of the electron energy spectra, primarily at low energies since Fierz interference scales like $\frac{m_e}{E}$. In 2010 the UCNA experiment at the Ultracold Neutron facility at Los Alamos Neutron Science Center took data for a beta decay asymmetry $A$ measurement. This same dataset can be used to extract the $b$ coefficient by comparing shifts in the nominal, i.e. $b = 0$, spectra to the data. Here we discuss Monte Carlo simulation methods used in both extracting a value of and estimating an error on $b$. We use Monte Carlo methods to generate the kinematics for beta decay corresponding to a range of $b$ values and input those kinematics to a GEANT4 simulation of the UCNA apparatus to create simulated beta spectra. This analysis focuses on the systematic errors due to non-linearities in the detector energy response which are modeled by converting simulated spectra into ``data-like'' spectra. The simulated spectra are compared against each other to extract a value of $b$ and an associated error. [Preview Abstract] |
Friday, October 14, 2016 4:12PM - 4:24PM |
FJ.00002: Simultaneous measurement of $\beta$ asymmetry and Fierz interference in neutron decay Kevin Hickerson The Standard Model allows for only vector and axial-vector charged and flavor changing currents. The proportion between these two currents is given by the axial-vector coupling constant, $g_A$, determined by the strong structure of the nucleon. This ratio cannot be computed exactly, but can be extracted by measuring the beta decay asymmetry parameter, $A$. Another parameter, the Fierz Interference term in neutron beta decay, $b_n$, serves as a test for non-Standard Model currents. A non-zero $b_n$ skews the peak of the beta energy spectrum and simultaneously dilutes the asymmetry in an energy dependent way, modifying the experimentally measured value of $A$. The UCNA experiment, at the Los Alamos Neutron Science Center in New Mexico, used ultracold neutrons to measure $A$, as well as put limits on $b_n$, and determine its impact on $A$. The largest obstacle to determining these limits is systematic effects associated with the energy calibration of the UCNA calorimetry system. We report on the results of new studies of these systematic effects using improved analysis techniques and simulations. [Preview Abstract] |
Friday, October 14, 2016 4:24PM - 4:36PM |
FJ.00003: Characterization of new materials for Ultracold Neutron transport and storage Edgard PIERRE, Nicholas CHRISTOPHER, Shinsuke KAWASAKI, Russell MAMMEI, James MARCELLIN, Ryohei MATSUMIYA, Ruediger PICKER At TRIUMF, we are currently developing a super-thermal UltraCold Neutron (UCN) source using phonon exchange in super-fluid helium. To take full advantage of the high density of UCN from the TRIUMF source we are developing high UCN transmission guides and long storage time volumes for polarized UCN. These guides and storage volumes are important for experiments requiring a high density of polarized UCN, such as the neutron Electric Dipole Moment (EDM) measurement. The transportation efficiency depends on the capacity of the guideās walls to contain the UCN. The mean potential experienced by a UCN on wall collisions is called the Fermi potential and depends on the material. We have determined a set of potential candidates for our next generation UCN guides and EDM storage chamber. Their Fermi potential was measured using the SOFIA apparatus at MLF, J-PARC, Japan. Results of this measurement are presented in this talk. [Preview Abstract] |
Friday, October 14, 2016 4:36PM - 4:48PM |
FJ.00004: PENTrack - a versatile Monte Carlo tool for ultracold neutron sources and experiments Ruediger Picker, Sanmeet Chahal, Nicolas Christopher, Martin Losekamm, James Marcellin, Stephan Paul, Wolfgang Schreyer, Pramodh Yapa Ultracold neutrons have energies in the hundred nano eV region. They can be stored in traps for hundreds of seconds. This makes them the ideal tool to study the neutron itself. Measurements of neutron decay correlations, lifetime or electric dipole moment are ideally suited for ultracold neutrons, as well as experiments probing the neutron's gravitational levels in the earth's field. We have developed a Monte Carlo simulation tool that can serve to design and optimize these experiments, and possibly correct results: PENTrack is a C++ based simulation code that tracks neutrons, protons and electrons or atoms, as well as their spins, in gravitational and electromagnetic fields. In addition wall interactions of neutrons due to strong interaction are modeled with a Fermi-potential formalism and take surface roughness into account. The presentation will introduce the physics behind the simulation and provide examples of its application. [Preview Abstract] |
Friday, October 14, 2016 4:48PM - 5:00PM |
FJ.00005: Magnetic Fields for Neutron Electric Dipole Moment Measurement at TRIUMF Taraneh Andalib The next generation of electric dipole moment (EDM) experiments are a good probe for Charge-Parity (CP) violating sources of physics beyond the Standard Model. The neutron EDM experiment at TRIUMF initially aims to measure the nEDM to ~$10^{-27}$ e$\cdot$cm by using a new superfluid He ultracold neutron (UCN) source and is expected to yield the highest density of UCN in the world. The experiment employs a room temperature Ramsey Resonance technique. One of the leading systematic uncertainties in the experiment is expected to arise from the magnetic fields fluctuations, where pT level stability over hundreds of seconds and $\sim$nT/m homogeneity is required. The stability of the magnetic field within a magnetically shielded volume is influenced by a number of factors such as the dependence of the internally generated magnetic field on the magnetic permeability $\mu$ of the shield material. Some experiments were conducted to measure the temperature dependence of the magnetic permeability of the shield material which is required to adequately design the next generation nEDM experiment at TRIUMF. [Preview Abstract] |
Friday, October 14, 2016 5:00PM - 5:12PM |
FJ.00006: $^{129}$Xe two-photon spectroscopy towards the neutron EDM experiment at TRIUMF Tomohiro Hayamizu, Emily Altiere, Eric Miller, Joshua Wienands, David Jones, Kirk Madison, Takamasa Momose Neutron EDM experiments are highly sensitive to fluctuations and inhomogeneities of magnetic fields inside neutron trap chambers. Precise measurements of magnetic fields are essential to measure small EDM frequency shifts of neutrons. In order to suppress these effects, we will introduce a Xe-Hg dual co-magnetometer to operate in the measurement cell. $^{129}$Xe was selected because it has a smaller neutron capture cross section than Hg, it is easy to control density, and it has two-photon excitation wavelengths close to Hg one-photon transition. We are planning to detect magnetic fluctuations by monitoring 823 nm and 895 nm emission intensity following a 252 nm two photon transition from 5p$^{6}$($^{1}$S$_{0}$) to 5p$^{5}$($^{2}$P$_{3/2}$)6p. We have observed this two photon transition and emission previously using a pulsed laser, and have recently constructed an intense 252 nm CW laser light source with the necessary hyperfine state resolution for the co-magnetometer operation. A UV enhancement cavity has been constructed to increase the excitation probability as well as to perform Doppler free spectroscopy of two-photon absorption. An avalanche photodiode (APD) is used to detect emission efficiently. We will report the present status of this measurement. [Preview Abstract] |
Friday, October 14, 2016 5:12PM - 5:24PM |
FJ.00007: High voltage studies of Xe-129 gas for the TRIUMF nEDM experiment Aikaterini Katsika One of the main sources of systematic uncertainties in neutron electric dipole experiments (nEDM) experiments is related to magnetic field fluctuations. The idea of the atomic co-magnetometer, where polarized atoms are introduced in the same volume with ultra-cold neutrons and measure the precession frequencies of both species, has been used in the past with Hg-199 atoms and led to an improvement of the nEDM upper limit down to 3.0\textbullet 10$^{\mathrm{-26}}$ e\textbullet cm. For the TRIUMF nEDM experiment, we aim to use Xe-129 atoms expecting to suppress this limit ultimately by two orders of magnitude more due to the smaller neutron absorption cross section and the negative (same to that of the neutron) gyromagnetic ratio that Xe-129 possesses. The precession of the Xe-129 atoms will be probed via a two photon exchange process which requires enough Xe-129 atoms such that the pressure in the cell is orders of mTorr. The talk will present the status of the experimental work carried out at TRIUMF which is focused on exploring the dielectric properties of the Xe-129 in the mTorr region as we require a stable electric field of about 12.5 kV/cm in order to improve the current nEDM upper limit. [Preview Abstract] |
Friday, October 14, 2016 5:24PM - 5:36PM |
FJ.00008: Characterization of a scintillating lithium glass ultra-cold neutron detector Lori Rebenitsch A new $^6$Li-glass ultra cold neutron detector was developed for the neutron Electric Dipole Moment (nEDM) experiment being prepared for the TRIUMF Ultra-Cold Neutron (UCN) source. The detector was characterized using the UCN source at the Paul Scherrer Institute (PSI). This talk will review detection of UCN with $^6$Li detectors, the detector and data acquisition design, and results of measurements of UCN data taken at PSI. Results presented will include a comparison of the relative rates of the detector channels, and a comparisons with a commercial Cascade detector. A detailed simulation of scintillation pulses and the data acquisition electronics was developed to estimate the efficiency and background contamination remaining when applying a pulse shape discrimination cut. One of the highlights will be on the processing and analysis of the data, including estimates of the background rejection, the effects of pileup, and the detector stability. [Preview Abstract] |
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