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 FG: Mini-symposium on Neutron and Nuclear Tests of CKM Unitarity IMini-Symposium
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Chair: Dan Melconian, Cyclotron Institute, Texas A&M Room: Pavilion Ballroom B |
Friday, October 14, 2016 4:00PM - 4:36PM |
FG.00001: Nuclear and Neutron Physics Tests of CKM Unitarity - Overview and Motivation Invited Speaker: Stefan Baessler The Cabbibo-Kobayashi-Maskawa (CKM) matrix describes quark mixing and CP violation in the Standard Model of Elementary Particle Physics (SM). One of the most precise tests of the SM is the verification of the unitarity of the CKM matrix in the first row: the verification that the sum of the squared elements in that row adds to unity. In my talk, I will introduce the theoretical motivation for that test, and I will introduce the most recent studies in nuclear and neutron beta decay, and I will show how their results can be used, in several independent ways, to perform the unitarity test. Finally, I will discuss the status of this test, which is less satisfactory than in previous years. [Preview Abstract] |
Friday, October 14, 2016 4:36PM - 4:48PM |
FG.00002: A Measurement of the Electron-Antineutrino Correlation in Free Neutron Beta Decay Alexander Komives The aCORN Collaboration has analyzed data taken on the NG-6 beamline at the NIST (National Institute of Standards and Technology) Center for Neutron Research and achieved the most precise measurement to date of the angular correlation (a-coefficient) between the electron and antineutrino emitted in free neutron beta decay. Such a measurement provides a test of the Electroweak Standard Model and, with the neutron lifetime, a determination of the weak vector and axial vector coupling constants that does not require a precise determination of the neutron polarization. aCORN employs a novel asymmetry method that leads to smaller systematic uncertainties compared to previous experiments that obtained the a-coefficient from the shape of the recoil proton energy spectrum. A brief description of the aCORN method, apparatus, result, and systematic effects will be presented. [Preview Abstract] |
Friday, October 14, 2016 4:48PM - 5:00PM |
FG.00003: Status of the Nab Experiment J. David Bowman The Nab experiment seeks to measure the electron-neutrino correlation coefficient, $a$, with a fractional uncertainty of .001. The experiment is now preparing for installation on the Fundamental Physics Beamline at ORNL-SNS. The angle between the electron and neutrino is reconstructed from the recoil proton time of flight in a magnetic field expansion spectrometer. I will review the principles of operation of the spectrometer, discuss the progress towards installation, and review the statistical and systematic uncertainty budgets. [Preview Abstract] |
Friday, October 14, 2016 5:00PM - 5:12PM |
FG.00004: The $a$SPECT experiment - an overview and latest results Christian Schmidt The $a$SPECT retardation spectrometer measures the $\beta$-$\nu$ angular correlation coefficient $a$ in free neutron $\beta$-decay. This measurement can be used to determine the ratio $\frac{g_A}{g_V}$ of the weak coupling constants, as well as to search for physics beyond the Standard Model. In 2013 $a$SPECT had a successful beam time at the Institut Laue-Langevin. The goal of this beam time is to improve the current uncertainty of $a$ from $\Delta a$/$a\approx 5\%$ to about $1\%$. The data analysis is in its final stage and nearly finished. In order to achieve an uncertainty of $1\%$, the systematics of $a$SPECT have to be understood accordingly. This is achieved by systematic tests and measurements of $a$ with different parameter settings for the spectrometer during the beam time. Additionally, offline measurements have been performed to determine the effect on the systematics, e.g. work-function fluctuations of the electrodes. These measurements are used as input for on-going simulations of the spectrometer to understand and reduce the systematic uncertainties further. In this talk $a$SPECT will be introduced and the current status of the data analysis will be reported, including a preliminary error budget of the systematic uncertainties. [Preview Abstract] |
Friday, October 14, 2016 5:12PM - 5:24PM |
FG.00005: Measurement of the weak magnetism form factor in $^6$He decay Oscar Naviliat-Cuncic, Xueying Huyan, Daniel Bazin, Alexandra Gade, Maximilian Hughes, Sean Liddick, Kei Minamisono, Shumpei Noji, Stanley Paulauskas, Anna Simon, Paul Voytas, Dirk Weisshaar The Fierz interference terms constitutes a very sensitive probe to searches for exotic scalar and tensor couplings in beta decay. It can directly be determined through measurements of the beta spectrum shape. To this end, the $^6$He decay happens to have a similar kinematic sensitivity than neutron decay despite its end-point is 4.5 larger; the electromagnetic and radiative corrections can be calculated accurately and, since the $^6$He ground state is member of an isospin triplet, hadronic contributions to the weak currents can be calculated using CVC. In this contribution we describe an experiment, performed at the National Superconducting Cyclotron Laboratory, which measures the shape of the beta energy spectrum in $^6$He decay. The technique is based on the implantation of the nuclei of interest in suitable detectors, eliminating thereby the major systematic effect in such measurements related to the back-scattering of beta particles in surrounding matter and detectors. The first goal is to measure the weak magnetism form factor, which has never been measured in $^6$He decay, and which will provide a sensitivity test of the technique. The status of the data analysis will be presented. [Preview Abstract] |
Friday, October 14, 2016 5:24PM - 5:36PM |
FG.00006: Precision measurement of the radiative $\beta$ decay of the free neutron Matthew Bales A continuous spectrum of photons is emitted in the decay of the free neutron. We present the results of the RDK II experiment, in which radiative photons were detected in coincidence with the electrons and protons from neutron decay. The experiment was performed on the NG-6 fundamental physics neutron beam line at the NIST Center for Neutron Research using two different photon detector arrays. An annular array of bismuth germanium oxide scintillators detected photons with energies between 14 keV and 782 keV and an array of large area avalanche photodiodes directly detected photons with energies between 0.4 keV and 14 keV . This experiment represents the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies. [Preview Abstract] |
Friday, October 14, 2016 5:36PM - 5:48PM |
FG.00007: First direct determination of the superallowed $\beta $-decay QEC-value for O-14 via Penning trap mass spectrometry at the LEBIT facility Ryan Ringle, Georg Bollen, Maxime Brodeur, Kortney Cooper, Martin Eibach, Kerim Gulyuz, Chris Izzo, David Morrissey, Matthew Redshaw, Rachel Sandler, Stefan Schwarz, Chandana Sumithrarachchi, Adrian Valverde, Antonio Villari Low-Z, superallowed $\beta $-emitters like O-14 are particularly significant for setting limits on the existence of scalar currents in the electroweak interaction. While the Conserved Vector Current (CVC) hypothesis states that Ft should be the same for all superallowed 0$+ \quad \to $ 0$+ \quad \beta $-decays, if there is a scalar interaction, an additional term approximately inversely proportional to QEC would be present in Ft. As QEC-values are smaller for lower-Z isotopes, these isotopes would be most sensitive to the presence of a scalar current, showing the largest deviation in Ft. To date, 14 Ft values are used to calculate the world average. Of these 14 decays, only O-14 had not been measured in a Penning trap, despite multiple attempts at other facilities. At LEBIT we have performed the first direct measurement of the ground state $\beta $-decay QEC value. This measurement provides an order of magnitude improvement in precision, and it no longer makes a significant contribution to the uncertainty of its associated Ft value. [Preview Abstract] |
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