Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session FJ: Mini-Symposium on Parity Violation and Fundamental Symmetries II |
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Chair: Adam Holley, Tennessee Technological University Room: Coronado |
Thursday, October 29, 2015 4:00PM - 4:12PM |
FJ.00001: A new measurement of the 129Xe EDM Timothy Chupp, Skyler Degenkolb, Natasha Sachdeva, Jared Cohn, Jake Huneau, Jaideep Singh, Peter Fierlinger, Eva Krageloh, Florian Kuchler, Tobias Lins, Mike Marino, Jonas Meinel, Benjamin Niessen, Stefan Stuiber, Michael Sturm, Martin Burghoff, Isaac Fan, Wolfgang Kilian, Silvia Knappe-Grueneberg, Allard Schnabel, Frank Siefert, Lutz Trahms, Jens Voigt, Earl Babcock, Zahir Salhi Although neutron, atom and molecular EDM measurements have set only upper limits, the motivation for more sensitive searches is stronger than ever. A recent global analysis of EDM results shows that the 95\% CL upper limit of $6\times 10^{-27}$ e-cm for $^{129}$Xe contributes to constraining several CP violating parameters and that improved sensitivity further probes beyond-Standard-Model CP violation. In a new effort using a $^3$He co-magnetometer, the gas mixture is polarized by spin-exchange optical pumping and then transferred to a cell in the FRM-II high-performance magnetically shielded room, where a SQUID magnetometer array measures the spin precession. Recent tests indicate EDM sensitivity $<$ 10$^{-28}$ e-cm in one-day. [Preview Abstract] |
Thursday, October 29, 2015 4:12PM - 4:24PM |
FJ.00002: Precision Measurements in $^{37}$K Melissa Anholm, Daniel Ashery, Spencer Behling, Benjamin Fenker, Dan Melconian, Michael Mehlman, John Behr, Alexandre Gorelov, Konstantin Olchanski, Claire Preston, Claire Warner, Gerald Gwinner We have performed precision measurements of the kinematics of the daughter particles in the decay of $^{37}$K. This isotope decays by $\beta^+$ emission in a mixed Fermi/Gamow-Teller transition to its isobaric analog, $^{37}$Ar. Because the higher-order standard model corrections to this decay process are well understood, it is an ideal candidate for for improving constraints on interactions beyond the standard model. Our setup utilizes a magneto-optical trap to confine and cool samples of $^{37}$K, which are then spin-polarized by optical pumping. This allows us to perform measurements on both polarized and unpolarized nuclei, which is valuable for a complete understanding of systematic effects. Precision measurements of this decay are expected to be sensitive to the presence of right-handed vector currents, as well as a linear combination of scalar and tensor currents. Progress towards a final result is presented here. [Preview Abstract] |
Thursday, October 29, 2015 4:24PM - 4:36PM |
FJ.00003: First direct determination of the superallowed $\beta $-decay Q$_{EC}$-value for $^{14}$O Kerim Gulyuz, Martin Eibach, Ryan Ringle, Stefan Schwarz, Chandana S. Sumithrarachchi, Georg Bollen, Kortney Cooper, Christopher Izzo, David J. Morrissey, Rachel Sandler, Adrian A. Valverde, Richard R. Bryce, Matthew Redshaw, Maxime Brodeur, Antonio C.C. Villari Superallowed 0$^{+}\to $0$^{+}$ nuclear $\beta $ transitions provide a sensitive test of the conserved vector current (CVC) hypothesis. While the CVC hypothesis calls for a constant corrected \textit{Ft}-value for all superallowed 0$^{+}\to $0$^{+} \beta $-decays, if there is a scalar interaction, an additional term approximately inversely proportional to Q$_{EC}$ would be present in \textit{Ft}. Hence the sensitivity to the presence of a scalar current would be larger for smaller Q$_{EC}$; i.e. for low-Z nuclei. Of the 14 \textit{Ft}-values that are used to calculate the world average, only the Q$_{EC}$ for $^{14}$O has not been measured in a Penning trap, despite multiple attempts at other facilities. We have performed the first direct measurement of the ground state $\beta $-decay Q$_{EC}$-value at the LEBIT facility. An order of magnitude improvement in precision makes it the most precisely known Q$_{EC}$-value for determining \textit{Ft} used in testing the CVC hypothesis. [Preview Abstract] |
Thursday, October 29, 2015 4:36PM - 4:48PM |
FJ.00004: High-precision half-life measurements for the superallowed $\beta^+$ emitter $^{10}$C Michelle Dunlop High precision measurements of the $ft$ values for superallowed Fermi beta transitions between 0$^+$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the unitary of the Cabibbo-Kobayashi-Maskawa matrix, the Conserved-Vector-Current hypothesis, as well as set limits on the existence of scalar currents in the weak interaction. Half-life measurements for the lightest of the superallowed emitters are of particular interest as the low-Z superallowed decays are most sensitive to a possible scalar current contribution. The half-life of $^{10}$C can be measured by directly counting the $\beta$ particles or by measuring the $\gamma$-ray activity following $\beta$ decay. Previous results for the $^{10}$C half-life measured via these two methods differ at the 1.3$\sigma$ level, motivating further measurements of the $^{10}$C half-life using both techniques. Recent $^{10}$C half-life measurements via both gamma-ray photo-peak and direct beta counting were performed at TRIUMF's Isotope Separator and Accelerator facility. This presentation will highlight the importance of these measurements and half-life results will be presented. [Preview Abstract] |
Thursday, October 29, 2015 4:48PM - 5:00PM |
FJ.00005: Field modeling for the aCORN electrostatic mirror Michael Mendenhall The aCORN experiment measures the angular correlation between the electron and neutrino emitted in free neutron beta decay, via an electron-proton momentum correlation asymmetry. This method relies on a highly uniform electric field to direct protons' longitudinal momentum towards a detector, while leaving transverse momentum unchanged. Deviations from ideal field uniformity require a significant correction and corresponding systematic uncertainty on the experimental result. Production of a uniform field is complicated by the requirement that the mirror region be mostly transparent to protons, leading to a design with a thin wire grid endcap. This talk describes evaluation of the aCORN electric field uniformity systematic; in particular, electrostatic field modeling near thin wire grids. Finite-element numerical calculations are compared to analytical approximations to build intuition and confidence about modeling this multi-length-scale configuration. [Preview Abstract] |
Thursday, October 29, 2015 5:00PM - 5:12PM |
FJ.00006: The data acquisition system for the aCORN experiment Maynard Dewey The aCORN experiment measures the angular correlation between the electron and neutrino emitted in free neutron beta decay, via an electron-proton momentum correlation asymmetry. Doing so requires detecting neutron beta decay protons and electrons in coincidence. Protons are detected with a surface barrier detector while electrons are detected with a large scintillator whose light output is parceled into 19 photomultiplier tubes. Additionally there are eight scintillators that detect backscattered electrons so that these events may be removed from the data stream. This talk will discuss the novel data acquisition system (both hardware and software) that has been developed to handle the high throughput rates observed. [Preview Abstract] |
Thursday, October 29, 2015 5:12PM - 5:24PM |
FJ.00007: Uncertainty and Systematic Corrections for the Neutron Polarization in the UCNA Experiment Eric Dees The UCNA experiment uses the decay of polarized ultracold neutrons (UCN) to measure the angular correlation A between the emitted electron's momentum and the initial polarization direction of the neutrons magnetic moment. As such, a precise determination of the average spin polarization of the neutron's population in the decay trap is required. By implementing a neutron reflecting shutter at the entrance of the decay trap, the residual UCN outside of the decay trap can be drained, thus dramatically increasing the signal to background ratio in the subsequent measurement of the depolarized fraction. However, our implementation of the shutter also involves a systematic correction associated with the evolution of the polarized and depolarized populations whilst trapped during this background draining phase. Our estimates of this correction come from Monte Carlo simulations of the neutron transport, constrained by direct measurements of the depolarization evolution by the shutter and direct measurements of the efficiency of our polarimetry technique. Current estimates of the uncertainty in determination of the polarization, the agreement between measured and simulated observables, along with predictions of the systematic evolution correction will be discussed. [Preview Abstract] |
Thursday, October 29, 2015 5:24PM - 5:36PM |
FJ.00008: Measuring the free neutron lifetime to $\leq$ 0.3s via the beam method Jonathan Mulholland, Nadia Fomin Neutron beta decay is an archetype for all semi-leptonic charged-current weak processes. A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is needed to predict the primordial ${}^4$He abundance from the theory of Big Bang Nucleosynthesis. An effort has begun for an in-beam measurement of the neutron lifetime with an 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] |
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