Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session CE: Fundamental Neutron Physics Measurements |
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Chair: Brad Filippone, California Institute of Technology Room: Simmons Ballroom 1 |
Friday, October 24, 2008 10:30AM - 10:42AM |
CE.00001: ABSTRACT WITHDRAWN |
Friday, October 24, 2008 10:42AM - 10:54AM |
CE.00002: Measurement of the Neutron Beta Decay Asymmetry by the UCNA Experiment Michael Mendenhall In free neutron beta decay, the direction of the emitted electron is correlated with the polarization of the decaying neutron. The asymmetry between spin-aligned and spin-antialigned electron emissions is a function of $\lambda$, the ratio of axial-vector and vector coupling constants. Together with the neutron lifetime, $\lambda$ can be used to determine $V_{ud}$ in the CKM matrix. Ultracold neutrons (UCN) are advantageous for measuring the decay asymmetry as they can be nearly 100\% polarized and minimize production of neutron-induced backgrounds. Presented here are results from the first measurement of the asymmetry using UCN, performed by the UCNA collaboration in 2007, and improvements for the higher-statistics measurements of this year. [Preview Abstract] |
Friday, October 24, 2008 10:54AM - 11:06AM |
CE.00003: Diamond-like-Carbon Coated Copper Guides for use in the UCNA Experiment: Production Techniques and Status R.R. Mammei, F.E. Pazuchanics, D.L. Richardson, R.B. Vogelaar, M.L. Pitt, A.R. Young The UCNA experiment at Los Alamos National Lab employs ultracold neutrons (UCN) to measure the beta-asymmetry in polarized neutron decay. Our current beam line makes use of polished stainless steel and copper guides to transport and bottle the UCN. Due to their high Fermi potential and low depolarization per bounce, utilizing Diamond-like-Carbon (DLC) coated copper guides to preserve polarization and transport UCN after they have been polarized has the potential of increasing the observed decay rate in our trap and reducing the size of polarization-related systematic errors. However there have been challenges in obtaining a well-adhered DLC coating on the copper substrate. In order to overcome this difficulty a variety of guide preparation and production processes have been developed to obtain an acceptable coating. A review of the methods and analysis of the resulting coatings will be discussed along with beta-decay rate results from installing these guides in our experiment. [Preview Abstract] |
Friday, October 24, 2008 11:06AM - 11:18AM |
CE.00004: Ultracold Neutron Nonimaging Optics Kevin P. Hickerson The design principles of nonimaging optics are applied to ultracold neutron (UCN) transport. In particular, a vertical compound parabolic concentrator (CPC) that efficiently redirects UCN vertically into a bounded spatial volume where they have a maximum energy $mga$ that depends only on the initial phase space cross sectional area $\pi a^2$ creates a spectrometer which can be applied to neutron lifetime experiments, gravitational quantum state experiments and n$\bar{\rm n}$ oscillation searches. [Preview Abstract] |
Friday, October 24, 2008 11:18AM - 11:30AM |
CE.00005: Measuring the Neutron Lifetime Using Magnetically Trapped Ultracold Neutrons H.P. Mumm, K.J. Coakley, A.K. Thompson, G. Yang, R. Golub, P.R. Huffman, C.M. O'Shaughnessy, K.W. Schelhammer, P. Seo, J.M. Doyle, L. Yang, S.K. Lamoreaux 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 is nearing completion at NIST. In our unique approach, a 8.9 Angstrom neutron beam is incident on a superfluid $^4$He target within the minimum field region of an Ioffe- type magnetic trap. Some neutrons are downscattered by single phonon emission in the superfluid 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. Statistical limitations of the previous apparatus as well as systematics related to neutron material bottling will be reduced by significant increases in field strength and trap volume. Tests of a new magnetic trap, cryostat, and details of the upgrade will be presented. [Preview Abstract] |
Friday, October 24, 2008 11:30AM - 11:42AM |
CE.00006: $^3$He Relaxation Time Measurement at $\sim$400mK for the neutron electric dipole moment (nEDM) experiment Qiang Ye, Franklin Dubose, Dipangkar Dutta, Haiyan Gao, Robert Golub, Paul Huffman In the new neutron electric dipole moment (nEDM) experiment which is planned to be carried out at the SNS, the neutron storage cell will be made of dTPB-dPS (a wavelength shifting material) coated acrylic and filled with superfluid $^4$He. The experiment will use the nuclear magnetic resonance technique to measure the neutron precession frequency by comparing with that of the polarized $^3$He using spin dependence of the nuclear absorption process: $\vec{n} + \vec{^{3}He} \rightarrow p + t + 764$ keV. The polarized $^3$He will be used as a co-magnetometer to monitor the magnetic field \emph{in situ} during the experiment. Understanding the relaxation mechanism of polarized $^3$He in the storage cell under the experimental conditions and maintaining $^3$He polarization is crucial. Following our earlier study of the $^3$He relaxation time in a dTPB-dPS coated cylindrical acrylic cell at a temperature of 1.9K in the presence of superfluid $^4$He at a magnetic holding field of 21 gauss, similar measurements at $\sim$400mK (the proposed nEDM experimental temperature) have been carried out using a dilution refrigerator at TUNL with the magnetic holding field of $\sim$7 gauss. Preliminary results will be presented. [Preview Abstract] |
Friday, October 24, 2008 11:42AM - 11:54AM |
CE.00007: A New Gravito-Magnetic Trap for Measuring the Neutron Lifetime using Ultracold Neutrons Kevin Hickerson Presently, there is a significant discrepancy between the previous most precise measurements of the neutron lifetime. To help resolve this, a new lifetime experiment is underway at the Los Alamos Neutron Science Center (LANSCE) using ultracold neutrons (UCN). Polarized UCN will be trapped by gravity in an asymmetric compound toroidal magnetic trap. The trap will be made of permanent magnets arranged in a high field gradient configuration called a Halbach array. The compound toroid combined with the rippled multipole field will quickly reduce the fraction of phase space of the trap that is quasi-bound, decreasing the probability that UCN escape or have material interactions during the lifetime measuring period. Removing these marginally trapped UCN addresses an important systematic effect in previous measurements. [Preview Abstract] |
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