Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session T13: Precision Low Energy |
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Sponsoring Units: DPF Chair: Ta Pei Cheng, University of Missouri-St. Louis Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis F |
Monday, April 14, 2008 3:30PM - 3:42PM |
T13.00001: Progress on Magnetic Trap Neutron Lifetime Experiment at Los Alamos Alexander Saunders A new neutron lifetime experiment has been designed and is now under construction at Los Alamos. This experiment eliminates material interactions of the neutrons by holding ultra-cold neutrons in a magnetic trap. The trap is closed on the bottom and sides by a high order multipole magnetic field produced by a Halbach array of permanent magnets and is closed on the top by gravity. The ultra-cold neutrons will be supplied by the source now operating at Los Alamos. Neutrons in quasi-bound orbits will be eliminated by the asymmetric shape of the trap. Approximately 10$^{6}$ neutrons will be stored per fill. First measurements of stored neutrons are expected in 2008. The design and construction status will be presented. [Preview Abstract] |
Monday, April 14, 2008 3:42PM - 3:54PM |
T13.00002: Precision Neutron Polarimetry Monisha Sharma, L Barron-Palos, J.D. Bowman, T.E. Chupp, C. Crawford, A. Danagoulian, A. Klein, S.I. Penttila, A.F Salas-Bacci, W.S. Wilburn Proposed PANDA and abBA experiments aim to measure the correlation coefficients in the polarized neutron beta decay at the SNS. The goal of these experiments is 0.1{\%} measurement which will require neutron polarimetry at 0.1{\%} level. The FnPB neutron beam will be polarized either using a $^{3}$He spin filter or a supermirror polarizer and the neutron polarization will be measured using a $^{3}$He spin filter. Experiment to establish the accuracy to which neutron polarization can be determined using $^{3}$He spin fliters was performed at Los Alamos National Laboratory in Summer 2007 and the analysis is in progress. The details of the experiment and the results will be presented. [Preview Abstract] |
Monday, April 14, 2008 3:54PM - 4:06PM |
T13.00003: Initial Asymmetry Results from the UCNA Experiement Robert Pattie Jr In the decay of free polarized neutrons, there is an asymmetry in the emission direction of electrons with respect to neutron spin, which is related to $\lambda$, the ratio of the axial-vector and vector coupling constants. By measuring this asymmetry and the neutron lifetime, it is possible to determine $V_{ud}$, the first element of the CKM matrix. The UCNA collaboration will be the first to measure this asymmetry using ultra-cold neutrons, which allow for nearly $100\%$ polarization and transport far from the source to reduce backgrounds. In 2007, all major systems required for a high precision measurement of the neutron beta-asymmetry were commissioned and a measurement with $\approx 3\%$ statistical uncertainty was performed. Analysis of these initial results will be presented. [Preview Abstract] |
Monday, April 14, 2008 4:06PM - 4:18PM |
T13.00004: UCN Polarization in the UCNA Experiment 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 experimental strategy is to transport UCN into a decay volume through a 7T static magnetic field, allowing the magnetic potential to polarize the UCN. UCN polarization can then be reversed via an rf adiabatic spin-flipper which sits between the 7T polarizing field and the decay volume. This spin-flipper also allows an \textit{in situ} measurement of the depolarized contamination which develops during a constant-polarization measurement cycle. In order to minimize this spin contamination the UCN guides leading to the decay volume, and the decay volume itself, are constructed of electropolished copper. Early in the 2007 run cycle measurements were made to determine the degree of polarization provided by the 7T polarizing field as well as the absolute efficiency of the spin-flipper. These results, together with the run-by-run depolarization measurements made during UCNA data-taking, can be used to determine the average depolarized fraction present during our beta-asymmetry measurements. Details of the polarization measurements and the limits they place on the spin contamination present in UCNA will be discussed and compared to expectations from Monte Carlo transport models. [Preview Abstract] |
Monday, April 14, 2008 4:18PM - 4:30PM |
T13.00005: Production of Ultracold Neutrons for the UCNA Experiment Raymond Rios Ultracold Neutrons (UCN) have temperatures below about 4mK and energies below about 300 neV. At this temperature, the neutron energy is within the Fermi surface potential range of some materials making it possible to transport and bottle neutrons which can be used for extremely low background neutron beta decay measurements. The UCNA collaboration has been commissioning a UCN source which incorporates moderating spallation neutrons off a tungsten target at the Los Alamos National Lab's 800 MeV proton beam facility, LANSCE, for polarized beta decay measurements. In the past year changes to the source have lead to more than an order of magnitude increase in UCN out into the experiment, making a significant step towards realizing a high precision UCN beta-asymmetry measurement. We will present an overview of the UCN source, the specific contributions of each of the major improvements from last year, and improvements planned for the 2008 run cycle. [Preview Abstract] |
Monday, April 14, 2008 4:30PM - 4:42PM |
T13.00006: Improvements to the UCNA Experiment for 2008 Run Cycle Mark Makela During 2007 many changes were made to the UCNA experiment and the Los Alamos UCN source; these changes allowed for a $\sim $3{\%} initial measurement of neutron decay correlation A in a 36 hour run. In 2008 several more changes are planned. These changes to the experiment and source will be discussed, as will the expected level of precision achievable in the 2008 run cycle. [Preview Abstract] |
Monday, April 14, 2008 4:42PM - 4:54PM |
T13.00007: Studies on Magnetometry and Samples used for an Experimental Search on the Electric Dipole Moment of the Electron using Solid-State Techniques Young Jin Kim, Craig Huffer, Maciej Karcz, Chen-Yu Liu, Goverdhan Reddy A discovery of a permanent electric dipole moment of the electron (eEDM) at the current sensitivity level will imply new sources of CP violation beyond the standard model of particle physics. We are attempting to improve the experimental limit of the eEDM using a new technique employing solid-state systems at low temperatures. The experiment requires a system with a large magnetic response and the application of sensitive SQUID magnetometry. In this talk, I will present results in characterizing the magnetic properties of our solid-state sample, polycrystalline Gadolinium Gallium Garnet (GGG), and discuss preliminary results of systematic studies on our SQUID detectors. In our current setup, SQUID sensors record a non-zero change in magnetic flux with no GGG samples. This non-zero signals indicate sources of systematic effects which mimic EDM signals. We identified that several sources are responsible for producing systematic errors: the eddy current and the transient current. The dominant effect due to the eddy current can be reduced by using electrode material with a high resistivity, such as graphite.. [Preview Abstract] |
Monday, April 14, 2008 4:54PM - 5:06PM |
T13.00008: Studies of Electrical Breakdown in Pressurized Superfluid Helium-4 for the SNS Neutron Electric Dipole Moment Experiment Maciej Karcz, Craig Huffer, Young Jin Kim, Chen-Yu Liu, Josh Long Investigation of the dielectric strength of liquid helium (LHe) is motivated by the search for the electric dipole moment of the neutron (nEDM) at the Spallation Neutron Source (SNS). The SNS nEDM experiment uses a magnetic resonance technique on neutrons in a working medium of LHe. To achieve sensitivity of nEDM to the level of $10^{-28}$ e-cm, it requires an electric field of 50 kV/cm applied inside LHe. Prior results indicated that sustaining such a field in superfluid LHe at sub-Kelvins might be problematic. We are carrying out detailed electrical breakdown studies at Indiana University Cyclotron Facility. Results of measurements show that the specified field can be repeatedly applied to de-pressurized superfluid helium at temperatures as low as 1.7 K using a pressurization cycle. The observed hysteretic behavior has never been reported and we are working towards understanding the mechanism. [Preview Abstract] |
Monday, April 14, 2008 5:06PM - 5:18PM |
T13.00009: Lowering the upper bound on the photon mass Dmitri Ryutov The photon mass in the framework of the Proca equations can be constrained by analyzing large-scale magnetic fields in space physics and astrophysics (Goldhaber A S, Nieto M M, Rev. Mod. Phys., v. 43, p. 277, 1971). The value of the photon mass currently recommended by the bi-annual compendium of the Particle Data Group (Yao W-M, and Particle Data Group, J. Phys. G v. 33, p. 1, 2006) is based on the analysis of the Solar wind at the Earth orbit (Ryutov D D, Plasma Phys. Control. Fusion, v. 39, p. A73, 1997). The present paper describes 100-fold reduction of the upper limit by analyzing the Solar wind at the Pluto orbit. Potential improvements related to the analysis of magnetic fields of even larger objects, ranging from Herbig-Haro jets to galaxy clusters, are discussed. The use of the virial theorem for such an analysis is found to be problematic. On the other hand, direct comparison of the observed dynamics of stellar outflows and dense molecular clouds with the predictions of magnetohydrodynamic equations accounting for the finite photon mass may lead to further improvements. [Preview Abstract] |
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