Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session CE: Electroweak Interactions I |
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Chair: Yordanka Ilieva, University of South Carolina Room: Coronado |
Thursday, November 4, 2010 8:30AM - 8:42AM |
CE.00001: Tuning the LANSCE proton beam for optimum ultracold neutron production Raymond Rios The UCNA experiment uses LANSCE's 800 MeV proton beam incident on a spallation tungsten target to ultimately generate ultracold neutrons (UCN). Optimizing the proton beam's alignment and size on the target has a direct relationship with the overall UCN production. The beam must be switched over daily from a separate experiment to the tungsten target and retuned. Standard beam diagnostics cannot be used within 8 m of the target due to the level of shielding that surrounds the target and extends up along the proton beam line. This presentation will detail the effectiveness of the various methods employed to obtain beam positioning and monitoring which include a cold neutron detector, drift fast neutron tube detector, inline MWPC beam profile monitor, and, the latest, a set of carefully positioned thermocouples. [Preview Abstract] |
Thursday, November 4, 2010 8:42AM - 8:54AM |
CE.00002: Advanced guide coating techniques for Ultracold Neutron transport Brittney VornDick The UCNA experiment utilizes ultracold neutrons (UCN) to measure angular correlations in beta-decay. UCN are produced in a solid deuterium source and then coupled to the experimental decay volume through a sequence of guide tubes. Requirements for the guides typically include smooth surfaces, high Fermi potentials, and often a very low depolarization probability per bounce. Studying different materials for the guides leads to greater efficiency for containing and transporting UCN. We review the UCNA guide geometry and characterize the effectiveness of recently developed diamond-like carbon coatings produced by pulsed laser deposition on electropolished Cu tubing in our decay volume and throughout the system. We also present research and development towards new coating processes and materials for UCN guides. [Preview Abstract] |
Thursday, November 4, 2010 8:54AM - 9:06AM |
CE.00003: Scattering Corrections in Neutron $\beta$-decay Angular Correlation Measurements Robert Pattie Measurements of angular correlations in neutron $\beta$-decay, such as the electron momentum-neutron spin correlation A, require precise knowledge of the energy and momentum of the emitted electron and or proton. However, accurate determination of these observables is often limited by our understanding of scattering from materials before detection. Over the past decade, the UCNA experiment has developed a PENELOPE-based Monte Carlo simulation to estimate this systematic effect on the measured $\beta$ asymmetry A. Other experiments, proposed and active, will measure angular correlations using similar detection methods. We will discuss our results as well as the general implications of these simulations as they apply to other detector geometries and electric/magnetic field profiles. [Preview Abstract] |
Thursday, November 4, 2010 9:06AM - 9:18AM |
CE.00004: UCNA Systematic Uncertainties Michael Mendenhall The UCNA experiment uses ultracold neutrons to measure the $A$ beta-decay angular correlation between electron emission direction and neutron spin. In 2007, an initial ``proof-of-principle'' statistics-limited data set was taken, providing a 4.4\% determination of $A_0$. For the higher statistics data set taken in 2008 and 2009, systematic uncertainties become increasingly important. This talk is an overview of the main systematic uncertainties (including decay-beta scattering and energy reconstruction, neutron polarization, and backgrounds) contributing to a 1.4\% determination of $A_0$ from the 2008-2009 data. [Preview Abstract] |
Thursday, November 4, 2010 9:18AM - 9:30AM |
CE.00005: New Results from UCNA's Effort to use Ultracold Neutrons in a $<$0.5\% Measurement of the Neutron Beta-Asymmetry A.T. Holley The goal of the UCNA experiment is to determine the angular correlation between the electron momentum and the neutron spin (the beta-asymmetry) in free neutron decay using polarized ultracold neutrons (UCN). The beta-asymmetry is one of several experimentally accessible values whose precise determination allows for stringent Standard Model tests, and UCN-based angular correlation experiments have the innate advantages of essentially 100\% initial neutron polarization and small neutron-generated backgrounds, both of which allow for good control over two of the typically important systematics in free neutron angular correlation measurements. The practical advantages and challenges of using UCN in such an experiment as well as the features of our beta spectrometer which provide the capability for high-precision work will be discussed in light of our completed analysis of data taken during 2008 and 2009, which led to a 1.4\% measurement of the beta-asymmetry. [Preview Abstract] |
Thursday, November 4, 2010 9:30AM - 9:42AM |
CE.00006: Searching for Fierz Interference in Beta Decay of Ultracold Neutrons Kevin Hickerson It is theorized that contributions to scalar and tensor interactions from physics beyond the Standard Model could be detectable in the spectrum of neutron beta decay, manifest as a nonzero value for the so-called Fierz interference parameter, $b$. Some minimally supersymmetric models may have $b$ as large as $10^{-3}$, which is within reach for measurement, but below the current limits set by superallowed $0+ \to 0+$ nuclear $\beta$ decays. We present a new experiment that uses the ultracold neutron (UCN) source at LANSCE for measuring $b$, in which UCN are guided into a shielded $4\pi$ calorimeter. The decay volume is a box with scintillator walls that both trap UCN and measure beta energy. The low background environment and high neutron density allows this experiment to set an improved upper limit of the Gamow-Teller component of $b$ for the free neutron. [Preview Abstract] |
Thursday, November 4, 2010 9:42AM - 9:54AM |
CE.00007: Calibration of the Neutron Lifetime Flux Monitor Through the Absolute Determination of Neutron Flux A. Yue, G. Greene, M. Dewey, D. Gilliam, J. Nico, A. Laptev The measurements of the neutron lifetime using ``bottled'' ultra-cold neutrons that claim the smallest experimental uncertainties are seriously discrepant with respect to each other. Given that the statistical contribution to their uncertainty is much smaller than the discrepancy, it is likely that one or more of these measurements suffers from a systematic effect yet to be definitively identified. In the most precise cold neutron beam measurement of the lifetime which gives $\tau_{n} = \left(886.3 \pm 3.4\right)$ s, the largest uncertainty was attributed to the absolute determination of the capture flux of the neutron beam. A new direct measurement of the neutron lifetime flux monitor efficiency using an absolute ``black'' neutron detector could reduce this contribution to the uncertainty. The Alpha-Gamma device is a ``black'' neutron detector based on the counting of 478 keV gamma rays from a totally absorbing ${}^{10}$B foil. Neutron flux is measured to a statistical precision of 0.1\,\% in several days of running. The Alpha-Gamma device has been used to calibrate the neutron lifetime flux monitor on a monochromatic beamline at the NIST Center for Neutron Research. The measurement technique and status of this calibration will be presented. [Preview Abstract] |
Thursday, November 4, 2010 9:54AM - 10:06AM |
CE.00008: Measuring the Neutron Lifetime using Magnetically Trapped Ultracold Neutrons H.P. Mumm, K.J. Coakley, M.S. Dewey, M.G. Huber, P.P. Hughes, A.K. Thompson, R. Golub, C.R. Huffer, P.R. Huffman, C.M. O'Shaughnessy, K.W. Schelhammer The neutron beta-decay lifetime is important in both theoretical predictions of the primordial abundance of $^{4}$He and providing a strong unitarity test of the CKM mixing matrix. We have previously demonstrated trapping of Ultracold Neutrons (UCN) in a magnetic trap, and, though statistically limited, measured a lifetime consistent with the world average. A major upgrade of the apparatus has now been completed at NIST. In our unique approach, a 0.89 nm neutron beam is incident on a superfluid $^{4}$He target within the minimum field region of an Ioffe-type magnetic trap. Neutrons are downscattered by single phonon scattering in liquid helium to near rest and trapped; at sufficiently low temperatures, the low phonon density in the helium suppresses upscatter. The electron accompanying neutron decay produces scintillation in the superfluid helium and can be detected in real time. Previous statistical limitations as well as systematics related to neutron material bottling will be reduced by significant increases in field strength and trap volume. Details of analyses of the systematics as well as the initial performance benchmarks of the new apparatus will be presented. [Preview Abstract] |
Thursday, November 4, 2010 10:06AM - 10:18AM |
CE.00009: Neutron Lifetime Experiment at LANL Steven Clayton, David Barlow, David Bowman, Vincenzo Cirigliano, Bradley Filippone, Kevin Hickerson, Gary Hogan, Adam Holley, Chen-Yu Liu, Mark Makela, Christopher Morris, Seppo Pentilla, Daniel Salvat, Alexander Saunders, Peter Walstrom, Albert Young A proposal will be presented for a new experiment, which has been developed with Los Alamos National Laboratory LDRD funding, to measure the neutron lifetime using ultracold neutrons in a magneto-gravitational trap. In the proposed experiment, an asymmetric bowl-shaped Halbach array of permanent magnets provides the levitating and laterally confining magnetic field for ultracold neutrons produced by the Los Alamos solid deuterium source. Quasi-trapped orbits, in which relatively fast neutrons may escape during the measurement period, are suppressed by the asymmetry of the bowl and small-scale field variations designed into the magnet array. Progress on the construction of the prototype apparatus will be described. [Preview Abstract] |
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