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 KG: Mini-symposium on Neutron and Nuclear Tests of CKM Unitarity - IIIMini-Symposium
|
Hide Abstracts |
Chair: Maxime Brodeur, University of Notre Dame Room: Pavilion Ballroom B |
Saturday, October 15, 2016 2:00PM - 2:12PM |
KG.00001: Current status of superallowed $0^+$$\rightarrow 0^+$ nuclear $\beta$ decay and the value of $V_{ud}$ J.C. Hardy, I.S. Towner, M. Bencomo, V.E. Iacob, H.I. Park, L. Chen, T. Eronen, V. Horvat, N. Nica Currently, the results from superallowed $0^+$$\rightarrow 0^+$ nuclear $\beta$ decays provide the most precise value for $V_{ud}$, the up-down element of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. According to the most recent critical survey of world data [1], the $ft$ values for 14 of these superallowed transitions have been established to a precision of order 0.1\% or better. These results, which cover a wide range of parent nuclei from $^{10}$C to $^{74}$Rb, constitute a very robust data set. After radiative and isospin-symmetry-breaking corrections have been applied, the resulting corrected ${\cal F} t$ values are all consistent with one another, demonstrating agreement with conservation of the vector current (CVC). With CVC upheld, the ${\cal F} t$-value results can then be averaged to obtain a value for $G_V$, the vector coupling constant, and for $V_{ud}$. Since the last survey closed, new measurements have appeared, which do not significantly change the conclusions in [1] but do reflect constructively on isospin symmetry breaking and on possible scalar currents. Up-to-date outcomes will be presented. \newline [1] J.C. Hardy and I.S. Towner, Phys. Rev. C 91, 025501 (2015). [Preview Abstract] |
Saturday, October 15, 2016 2:12PM - 2:24PM |
KG.00002: Precision Half-life Measurement of $^{17}$F Jacob Long, Maxime Brodeur Precision measurements have led to considerable advances in understanding in several areas of physics, including fundamental symmetry. The precise determination of $ft$ values for superallowed mixed transitions between mirror nuclides could provide an avenue to test the theoretical corrections used to extract the V$_{ud}$ matrix element from superallowed pure Fermi transitions. The calculation of the $ft$ value requires knowledge of the half-life, branching ratio, and Q value. Thus the $^{17}$F decay is particularly interesting as it proceeds completely to the ground state of $^{17}$O, which removes the need for branching ratio measurements. In the addition the largest uncertainty on the relevant $ft$ value of the $^{17}$F mirror transition stems from the uncertainty in the half-life. An experiment to determine this life-time was conducted by the $\beta$ counting of implanted $^{17}$F on a Ta foil that was removed from the beam for counting. The $^{17}$F beam was produced by a transfer reaction and separated by the TwinSol facility of the Nuclear Science Laboratory of the University of Notre Dame. The results for $^{17}$F will be presented together with preliminary results of more recent half-life measurements. This work is supported in part by the National Science Foundation. [Preview Abstract] |
Saturday, October 15, 2016 2:24PM - 2:36PM |
KG.00003: $^{20}$F beta spectrum shape and weak interaction tests Paul Voytas, Elizabeth George, Thomas Chuna, Oscar NAVILIAT-CUNCIC, Max Hughes, XUEYING HUYAN, Kei MINAMISONO, Stanley Paulauskas Precision measurements of the shape of beta spectra can test our understanding of the weak interaction. We are carrying out a measurement of the shape of the energy spectrum of $\beta$ particles from $^{20}$F decay. The primary motivation is to test the so-called strong form of the conserved vector current (CVC) hypothesis. The measurement should also enable us to place competitive limits on the contributions of exotic tensor couplings in beta decay. We aim to achieve a relative precision better than 3\% on the linear contribution to the shape. This represents an order of magnitude improvement compared to previous experiments in $^{20}$F. In order to control systematic effects, we are using a technique that takes advantage of high energy radioactive beams at the NSCL to implant the decaying nuclei in scintillation detectors deeply enough that the emitted beta particles cannot escape. The $\beta$-particle energy is measured with the implantation detector after switching off the implantation beam. Ancillary detectors are used to identify the 1.633-MeV $\gamma$-rays following the $^{20}$F $\beta$ decay for coincidence measurements in order to tag the transition of interest and to reduce backgrounds. We report on the status of the analysis. [Preview Abstract] |
Saturday, October 15, 2016 2:36PM - 2:48PM |
KG.00004: Overview of progress on the UCNtau Experiment Nathan Callahan The UCN$\tau$ experiment measures the free neutron lifetime by trapping Ultracold Neutrons (UCN) in a magneto-gravitational trap. Neutrons are confined below by a magnetic field from a permanent magnet Halbach array and above by gravity and undergo $\beta$ decay. The trap is filled through a removable trap section and the surviving UCN population is measured to extract the trap lifetime. Spectral cleaning of potentially escaping UCN is achieved using a movable plane of polyethylene that up-scatters neutrons to thermal energy and out of the trap. An active \textit{in-situ} detector is used to measure the neutron population. The detector uses $^{10}$B coated ZnS:Ag to detect UCN. The goal of the UCN$\tau$ experiment is to perform multiple 1s statistical measurements of the trap lifetime. Multiple 1s measurements in a single run cycle will allow UCN$\tau$ to study systematic effects including cleaning and phase space evolution. In the 2015-2016 run cycle at the Los Alamos Neutron Science Center, UCN$\tau$ commissioned a new active detection scheme, conducted systematic effect studies, and gathered sufficient statistics for a 1s trap lifetime measurement. An overview of updates to the apparatus will be presented in addition to a description of data collected. [Preview Abstract] |
Saturday, October 15, 2016 2:48PM - 3:00PM |
KG.00005: Progress toward a new beam measurement of the neutron lifetime Shannon Fogwell Hoogerheide Neutron beta decay is the simplest example of nuclear beta decay. A precise value of the neutron lifetime is important for consistency tests of the Standard Model and Big Bang Nucleosysnthesis models. The beam neutron lifetime method requires the absolute counting of the decay protons in a neutron beam of precisely known flux. Recent work has resulted in improvements in both the neutron and proton detection systems that should permit a significant reduction in systematic uncertainties. A new measurement of the neutron lifetime using the beam method will be performed at the National Institute of Standards and Technology Center for Neutron Research. The projected uncertainty of this new measurement is 1 s. An overview of the measurement and the technical improvements will be discussed. [Preview Abstract] |
Saturday, October 15, 2016 3:00PM - 3:12PM |
KG.00006: BL3: A Next Generation Beam Neutron Lifetime Experiment F. E. Wietfeldt, N. Fomin, G. L. Greene, W. M. Snow, C.-Y. Liu, C. B. Crawford, W. Korsch, B. Plaster, G. L. Jones, B. Collett, M. S. Dewey BL3 (Beam Lifetime 3) is a proposed next generation neutron lifetime experiment using the beam method. It continues a program, spanning more than three decades, of experiments at the ILL (France) and the NIST Center for Neutron Research that achieved the most precise beam method neutron lifetime measurements to date. A collimated cold neutron beam passes through a quasi-Penning trap where recoil protons from neutron decay are trapped. Periodically the trap is opened and these protons follow a bend in the magnetic field to a silicon detector. The same neutron beam passes through a thin-foil neutron counter that measures the neutron density. The ratio of neutron and proton count rates, along with efficiency factors, gives the neutron lifetime. The main goal of BL3 is to thoroughly investigate and test systematic effects in the beam method in an effort to address the current 4$\sigma$ discrepancy between the beam and bottle methods. It will employ a much larger, higher flux neutron beam, a large area position-sensitive proton detector, and an improved magnet design, with a proton trapping rate 100 times higher than past experiments. [Preview Abstract] |
Saturday, October 15, 2016 3:12PM - 3:24PM |
KG.00007: UCNA 2011-2013 Data Update Michael Brown The UCNA Experiment at the Ultracold Neutron facility at LANL uses polarized ultracold neutrons (UCN) to determine the neutron $\beta$-decay asymmetry parameter $A_0$, the angular correlation between the neutron spin and the decay electron's momentum. $A_0$ further determines $\lambda=g_A/g_V$, which, when combined with the neutron lifetime, permits extraction of the CKM matrix element $V_{ud}$ solely from neutron decay. In the UCNA experiment, UCN are produced in a pulsed, spallation driven solid deuterium source, polarized using a 7 T magnetic field, and transported through an Adiabatic Fast Passage (AFP) spin flipper prior to storage within a 1 T solenoidal spectrometer housing electron detectors at each end. The spin-flipper allows one to form a super-ratio of decay rates for neutron spins aligned parallel and anti-parallel to the 1 T magnetic field, eliminating to first order errors due to variations in the decay rate and detector efficiencies. Previous UCNA results from data taken in 2010 and earlier were limited by systematic uncertainties, particularly those from the UCN polarization, calibration of the electron energy, and electron backscattering and acceptance effects. Recent work addressing these systematics for data from run periods in 2011-2013 will be presented. [Preview Abstract] |
Saturday, October 15, 2016 3:24PM - 3:36PM |
KG.00008: Measurement of the beta asymmetry in $^{19}$Ne and a new determination of $V_{ud}$. Leah J. Broussard, Frank Calaprice, Gordon Jones, Albert Young A new analysis of the 1996 Princeton $^{19}$Ne beta asymmetry experiment was undertaken with particular emphasis on correcting for the effect of positron scatters off of the detector faces. The experiment was simulated using the Monte Carlo package PENELOPE. Applying the correction generated by the simulation to the data yields a zero energy intercept of the asymmetry (A$_0$) with a 2.0% uncertainty. The value of the element V$_{ud}$ in the CKM matrix which describes quark mixing is calculated. Using the value of the asymmetry from the Princeton experiment and the average from the results of all published $^{19}$Ne lifetime measurements, V$_{ud}$ is extracted with an uncertainty of 0.12%; the most precise value from a mirror decay (including the neutron). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700