Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session PG: Mini-Symposium on Fundamental Symmetries III |
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Chair: Robert Pattie, Los Alamos National Laboratory Room: Marquis A |
Saturday, October 28, 2017 10:30AM - 10:42AM |
PG.00001: High-Precision Half-Life Measurement for the Superallowed $\beta^+$ Emitter $^{22}$Mg Michelle Dunlop High precision measurements of the $\mathcal{F}t$ values for superallowed Fermi beta transitions between $0^+$ isobaric analogue states allow for stringent tests of the electroweak interaction. These transitions provide an experimental probe of the Conserved-Vector-Current hypothesis, the most precise determination of the up-down element of the Cabibbo-Kobayashi-Maskawa matrix, and set stringent limits on the existence of scalar currents in the weak interaction. To calculate the $\mathcal{F}t$ values several theoretical corrections must be applied to the experimental data, some of which have large model dependent variations. Precise experimental determinations of the $ft$ values can be used to help constrain the different models. The uncertainty in the $^{22}$Mg superallowed $\mathcal{F}t$ value is dominated by the uncertainty in the experimental $ft$ value. The adopted half-life of $^{22}$Mg is determined from two measurements which disagree with one another, resulting in the inflation of the weighted-average half-life uncertainty by a factor of 2. The $^{22}$Mg half-life was measured with a precision of 0.02\% via direct $\beta$ counting at TRIUMF's ISAC facility, leading to an improvement in the world-average half-life by more than a factor of 3. [Preview Abstract] |
Saturday, October 28, 2017 10:42AM - 10:54AM |
PG.00002: Precision lifetime measurement of $^{15}$O Daniel Burdette, Tan Ahn, Jacob Allen, Daniel Bardayan, Frederick Becchetti, Drew Blankstein, Maxime Brodeur, Bryce Frentz, Matthew Hall, James Kelly, James Kolata, Jacob Long, Patrick O'Malley, Bradley Schultz, Sabrina Strauss, Adrian Valverde As one of the most tested scientific theories, the Standard Model (SM) provides a complex but incomplete description of matter in the universe. There is currently a strong campaign to probe physics beyond the SM from various avenues on both the energy and precision frontiers. One such example on the precision side is ensuring the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, which requires a measurement of V$_{ud}$ that is both precise and accurate. This can be achieved through comparative half-life measurements of super-allowed beta decays. Pure Fermi cases have gotten a majority of the attention but mixed transitions are gaining interest as they can provide a mean to test the accuracy of V$_{ud}$. Aligning with these interests, the half-life of $^{15}$O has been measured using a beta counting station after the $TwinSol$ facility of the Nuclear Science Laboratory at the University of Notre Dame. The new half-life provides a more robust determination of the $ft$ value of the transition in anticipation of future measurements of the Fermi to Gamow-Teller mixing ratio. [Preview Abstract] |
Saturday, October 28, 2017 10:54AM - 11:06AM |
PG.00003: Precision Half-life Measurement of $^{25}$Al Jacob Long, Tan Ahn, Jacob Allen, Daniel Bardayan, Fredrich Becchetti, Drew Blankstein, Maxime Brodeur, Daniel Burdette, Bryce Frentz, Matthew Hall, James Kelly, James Kolata, Patrick O’Malley, Bradley Schultz, Sabrina Strauss, Adrian Valverde In recent years, precision measurements have led to considerable advances in several areas of physics, including fundamental symmetry. 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. Calculation of the $ft$ value requires the half-life, branching ratio, and Q value. $^{25}$Al decay is of particular interest as its half-life is derived from a series of conflicting measurements, and the largest uncertainty on the $ft$ value stems from the half-life uncertainty. The life-time was determined by the $\beta$ counting of implanted $^{25}$Al on a Ta foil that was removed from the beam for counting. The $^{25}$Al 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 $^{25}$Al results will be presented with preliminary results of more recent half-life measurements. [Preview Abstract] |
Saturday, October 28, 2017 11:06AM - 11:18AM |
PG.00004: Searching for Tensor Currents in the Weak Interaction Using $^{8}$Li $\beta$ Decay M.T. Burkey, G. Savard, R.E. Segel, J.A. Clark, J. Klimes, N.D. Scielzo, A.T. Gallant, K. Kolos, S.W. Padgett, B.S. Wang, T. Hirsh, E. Heckmaier, S.T. Marley, G. Morgan, R. Orford, K.S. Sharma The Standard Model’s description of the weak interaction follows a pure vector-axial-vector structure. Any observation of scalar or tensor contributions would indicate new physics. We will present preliminary analysis of a calibrated, high-statistics, $^{8}$Li beta decay data set taken with the Beta decay Paul Trap (BPT) at Argonne National Lab that has been used to precisely measure the tensor current-sensitive $\beta-\nu$ correlation coefficient (a$_{\beta\nu}$). This data set contains over ten times more statistics with reduced systematic effects compared to our collaboration’s previous experiment, which constrained a$_{\beta\nu}$ to ~1 percent of its predicted value and improved on the previous best limit set by $^{6}$He in 1963. Upon completion of the analysis, we are poised to further constrain the value of a$_{\beta\nu}$ to approximately 0.1 percent relative uncertainty. [Preview Abstract] |
Saturday, October 28, 2017 11:18AM - 11:30AM |
PG.00005: The in-situ detector for the UCN$\tau$ Neutron Lifetime Experiment Chris Cude-Woods We will present the design and the performance of the in-situ neutron detector used in the UCN$\tau$ experiment. When inserted into the UCN$\tau$ trap at the end of each neutron storage period, the detector counts the surviving ultracold neutrons with a high efficiency over ~10 seconds. It can also be placed at various heights to monitor changes in the phase space distribution of trapped neutrons. The detector is a large-area scintillating sheet coupled to wavelength-shifting fibers bundled and read out by two photomultiplier tubes. Low-energy neutrons are captured on a thin $^{10}$B layer (nominally 25nm) deposited on a ZnS:Ag screen. The resulting alpha particles and Li ions generate scintillation light in the ZnS. Due to the low light collection efficiency of the fiber arrangement, we record individual photon arrival times. The long ZnS scintillation decay time (several micro-seconds) presents challenges for event reconstruction at high neutron capture rates and can lead to significant corrections as the UCN$\tau$ apparatus routinely traps ~40K neutrons. We will discuss several rate-dependent corrections and compare two methods of lifetime analysis, one based on event reconstruction and the other on single photon counting. [Preview Abstract] |
Saturday, October 28, 2017 11:30AM - 11:42AM |
PG.00006: Measuring the free neutron lifetime to $\leq$ 0.3s via the beam method Nadia Fomin Neutron beta decay is an archetype for all semi-leptonic charged-current weak processes. While of interest as a fundamental particle property, a precise value for the neutron lifetime is also required for consistency tests of the Standard Model as well as to calculate the primordial $^4$He abundance in Big Bang Nucleosynthesis models. An effort has begun to develop an in-beam measurement of the neutron lifetime with a projected $\leq$ 0.3s uncertainty. This effort is part of a phased campaign of neutron lifetime measurements based at the NIST Center for Neutron Research, using the Sussex-ILL-NIST technique. Recent advances in neutron fluence measurement techniques as well as new large area silicon detector technology address the two largest sources of uncertainty of in-beam measurements, paving the way for a new measurement. The experimental design and projected uncertainties for the 0.3s measurement will be discussed. [Preview Abstract] |
Saturday, October 28, 2017 11:42AM - 11:54AM |
PG.00007: The Alpha-Gamma Program at NIST Evan Adamek The Alpha-Gamma device utilizes ${}^{10}$B(n,$\alpha$) capture on a totally absorbing deposit to measure the absolute neutron flux of a monochromatic cold neutron beam. This device has been successfully operated and used to improve the determination of the neutron flux for a neutron lifetime experiment. It is also being used for a measurement of the ${}^6$Li(n,t)${}^4$He cross section. We shall present its principle of operation along with the current and planned projects involving the Alpha-Gamma device, including the recalibration of the U.S. national neutron standard NBS-1, a ${}^{235}$U cross section measurement, and the calibration of flux monitors for a new measurement of the neutron lifetime [Preview Abstract] |
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