Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session ED: Mini-Symposium on Fundamental Neutron Physics II |
Hide Abstracts |
Chair: Chen-Yu Liu, Indiana University Room: Newport News Marriott at City Center Grand Salon IV |
Friday, October 12, 2007 2:00PM - 2:12PM |
ED.00001: Search for a neutron electric dipole moment Paul Huffman The possible existence of a nonzero electric dipole moment (EDM) of the neutron is of great fundamental interest in itself and directly impacts our understanding of the nature of electro-weak and strong interactions. The experimental search for this moment has the potential to reveal new sources of T and CP violation and to challenge calculations that propose extensions to the Standard Model. The goal of the current experimental effort is to significantly improve the measurement sensitivity to the neutron EDM over what is reported in the literature. The experiment has the potential to either measure the magnitude of the neutron EDM or to lower the current experimental limit by two orders of magnitude. Achieving these objectives will have a major impact on our understanding of the physics of both weak and strong interactions. An overview of the experiment and the present status of our R\&D effort will be presented. [Preview Abstract] |
Friday, October 12, 2007 2:12PM - 2:24PM |
ED.00002: Magnetic Field Finite-Element Calculations for the SNS Neutron EDM Experiment S. Balascuta, R. Alarcon, B. Filippone, B. Plaster, R. Schmid The nEDM experiment is a new search for the electric dipole moment (EDM) of the neutron with a sensitivity of 10$^{-28}$ \textit{e-cm} at the recently constructed Spallation Neutron Source (SNS). The measurement requires a static magnetic field surrounding two target cells that contain superfluid $^{4}$He, polarized neutrons and polarized $^{3}$He atoms. The latter are used as a co-magnetometer and ultracold neutron spin precession frequency analyzer. The applied static magnetic field, $B_{0}$, is chosen to be about 10 mG resulting in a precession of the magnetic moments for both neutrons and $^{3}$He nuclei of $\sim $30 Hz. To maintain the polarization of the neutrons and $^{3}$He atoms, the magnetic field should be very uniform with gradients of the order of 0.1 $\mu$G/cm~averaged over each cell volume. A separate requirement on the volume-averaged magnetic field gradient $<$dB$_{x}$/dx$>$ in the direction of $B_{0}$ of less than 0.01 $\mu$G/cm is necessary to minimize false EDM signals. In addition, to reduce the influence of ambient external fields an overall magnetic shielding factor of $\sim $10$^{5}$ is required. We present finite-element calculation results for the complete nEDM static magnetic field configuration including magnetic field gradients and $^{3}$He relaxation rates. [Preview Abstract] |
Friday, October 12, 2007 2:24PM - 2:36PM |
ED.00003: Monte Carlo Simulation of Spin Relaxation due to v $\times$ E effect in nEDM experiment Riccardo Schmid, Brad Plaster, Bradley Filippone We have simulated the precession of spin-polarized Ultra Cold Neutrons and $^{3}$He atoms in uniform and static {\it B} and {\it E} fields and calculated the spin relaxation. The spin relaxation times $T_1$ (longitudinal) and $T_2$ (transverse) of spin-polarized UCN and $^3$He atoms are important considerations in the new measurements of neutron Electric Dipole Moment in the SNS nEDM experiment. The uniform {\it E} field creates a motional magnetic field due to the {\nolinebreak$\vec{v} \times \vec{E}$} effect which combines with collisions with the walls of the holding cell to produce constant variation of the total {\it B} field and result in the spin relaxation of the neutron and $^3$He samples. Scattering of $^3$He atoms in $^4$He also results in spin relaxation and is highly temperature dependent. In the SNS nEDM experiment the {\it B} field has magnitude of 10 mGauss. The applied {\it E} field is parallel to the {\it B} field and has a magnitude of 50 kV/cm. We have found the relaxation times for the neutron due to the {\nolinebreak$\vec{v} \times \vec{E}$} effect to be long compared to holding times and neutron lifetime. On the other hand, the {\nolinebreak$\vec{v} \times \vec{E}$} effect could be important for $^3$He relaxation times. [Preview Abstract] |
Friday, October 12, 2007 2:36PM - 2:48PM |
ED.00004: The $^3$He injection test for the experiment on the neutron electric dipole moment search Xiaofeng Zhu A non-zero value of the neutron electric dipole moment (nEDM) is a direct consequence of the time reversal symmetry violation. As such it offers new insight into CP violation and has the potential for discovering new physics beyond the Standard Model. A new search for nEDM aiming at an two-order-of-magnitude improvement over the current experimental limit is underway. This new experiment is based on the nuclear magnetic resonance technique. The overall experimental strategy is to form a three-component fluid of ultracold neutrons (UCN) and $^{3}$He atoms dissolved in a bath of superfluid $^{4}$He at a temperature around 300 mK. The goal of the injection test is to study methods of injecting the $^3$He, polarized by an existing and tested atomic beam source, into the superfluid $^4$He and demonstrate that this can be done with acceptable polarization losses. Cryogenic problems associated with the injection aparatus will also be studied. The test will take place at the Los Alamos National Laboratory in the fall of 2007. [Preview Abstract] |
Friday, October 12, 2007 2:48PM - 3:00PM |
ED.00005: Investigation of Removal of $^{3}$He from Liquid $^{4}$He Solution for the Neutron Electric Dipole Moment Measurement David G. Haase, Robert Golub, Paul R. Huffman The measurement cycle for the proposed experiment to measure the neutron electric dipole moment at the SNS includes the injection and removal of polarized $^{3}$He, which is used as a comagnetometer in the same 15 liters of superfluid $^{4}$He which trap the ultracold neutrons. A critical part of the process is the removal of $^{3}$He atoms at the end of data collection, reducing the $^{3}$He concentration from 10$^{-10}$ to 10$^{-12}$ in a period of 100-200 seconds. It is proposed to accomplish the task via diffusion of the $^{3}$He from the target cell to an evaporator which preferentially removes $^{3}$He vapor. The efficiency of the process is strongly sensitive to the temperature dependent diffusion rate and vapor pressure of $^{3}$He as well as the superfluid film flow in $^{4}$He. We describe the design of this process and initial results from a prototype evaporator implemented at NC State University. [Preview Abstract] |
Friday, October 12, 2007 3:00PM - 3:12PM |
ED.00006: $n - \bar{n}$ oscillations in deuterium Bingwei Long, Ubirajara van Kolck Neutron-antineutron ($n - \bar{n}$) oscillation requires interactions that change baryon number by 2 units ($\delta B=2$), hence providing a stage for physics beyond Standard Model. We generalize the pionless nuclear effective field theory to include $\delta B=2$ interactions, and examine $n - \bar{n}$ oscillation in vacuum and in nuclei. We provide, in leading order in a controlled expansion, a model-independent link between the $n - \bar{n}$ vacuum oscillation time and the lifetime of deuteron. We compare our result with previous model estimates, and discuss extensions to other nuclei and to subleading orders. [Preview Abstract] |
Friday, October 12, 2007 3:12PM - 3:24PM |
ED.00007: Status of the Ultracold Neutron Source at Los Alamos National Lab R. Rios The ultracold neutron (UCN) source at Los Alamos (LANL) is currently in its third year of operation. High energy neutrons are produced via spallation from the LANSCE 800 MeV proton beam directed onto a tungsten target. These neutrons are then reflected and partially moderated in a Be ``flux trap'' (surrounded also by a layer of graphite), within which is located a cold polyethylene moderator. A small percentage of the cold neutrons are downscatttered within solid deuterium to colder temperatures (1-4 mK) and are then guided to the experimental area through 4-in diameter stainless steel guides. Modifications were made to the source for the 2006 and 2007 run cycles to increase UCN production. This talk will give an overview of the LANL UCN source, it's current status, and results from the 2006 and 2007 source test runs. [Preview Abstract] |
Friday, October 12, 2007 3:24PM - 3:36PM |
ED.00008: Status of the UCNA Experiment: A Measurement of the Neutron Beta-Asymmetry with Ultracold Neutrons Brad Plaster The UCNA experiment at the Los Alamos Neutron Science Center (LANSCE) has been designed to extract a precise value (goal of 0.2\%) for the neutron beta-asymmetry from measurements of the angular correlation between the neutron spin and the electron momentum (the beta-asymmetry) in polarized ultracold neutron beta-decay. Ultracold neutrons are produced by the downscattering of spallation neutrons in a solid deuterium source, spin-polarized via transport through a 7.0-Tesla field, and then directed to the center of a cylindrical decay trap situated within a solenoidal electron spectrometer. A status report on progress towards a first-step measurement of the beta-asymmetry at the $\sim 1$\% level during the LANSCE 2007 running cycle will be presented. [Preview Abstract] |
Friday, October 12, 2007 3:36PM - 3:48PM |
ED.00009: Studies of the Production and Transport of Highly Polarized Ultracold Neutrons for 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 neutron decay using polarized ultracold neutrons (UCN). The experimental strategy is to transport UCN into a decay volume through a 7T static magnetic field using the magnetic potential to polarize the UCN. The initial UCN spin can then be reversed via an rf adiabatic spin-flipper in a 1T field region whose gradient is tailored to optimize the adiabatic spin-flipper's performance. The spin-flipper, which also allows \textit{in situ} measurement of the UCN depolarization rate, is a resonant `bird-cage' cavity capable of producing rf fields in excess of 5G at 30Mhz. In order to minimize the UCN depolarization rate, UCN guides are constructed of diamond-like carbon films on quartz tubing, a technology which has been demonstrated to produce less than $3\times10^{-3}$ depolarizations per bounce. The performance of this system will be described, and compared to expectations from detailed Monte Carlo transport models. The implications for high precision measurements of polarized ultracold neutrons will also be discussed. [Preview Abstract] |
Friday, October 12, 2007 3:48PM - 4:00PM |
ED.00010: An Experiment for the Precision Measurement of the Radiative Beta Decay Mode of the Free Neutron R.L. Cooper, T.E. Chupp, K.J. Coakley, M.S. Dewey, B.M. Fisher, T.R. Gentile, J.S. Nico, A.K. Thompson, F.E. Wietfeldt, E.J. Beise, H. Breuer, H.P. Mumm, J. Byrne We have completed a measurement of the neutron radiative beta-decay branching ratio to 10\% relative standard uncertainty (15-340 keV photons). The goal of the next generation experiment is to perform a precision measurement of the branching ratio and the photon energy spectrum to a few percent. To reduce the statistical and systematic uncertainties, a 12-element detector is being developed to operate in the bore of a superconducting magnet. It consists of 12 inorganic, scintillating crystals coupled to avalanche photodiodes. Results from tests of the detector's operation and response using a small dewar and external gamma-ray sources will be presented. Monte Carlo modeling of the detector response is necessary to extract the photon energy spectrum and understand systematic effects. We also present a method to examine the consistency of the electron-proton coincidence rate with known properties of neutron beta decay. By improving calibrations and benchmarks, this experiment can better utilize the expected increase in detected events to make an accurate measurement of the branching ratio and photon energy spectrum. [Preview Abstract] |
Friday, October 12, 2007 4:00PM - 4:12PM |
ED.00011: Results of the first beam time with the neutron decay spectrometer $a$SPECT Stefan Bae\ss{}ler, Fidel Ayala Guardia, Michael Borg, Klaus Eberhardt, Werner Heil, Gertrud Konrad, Raquel Mu\~noz Horta, Yuri Sobolev, Igor Konorov, Gerd Petzoldt, Martin Simson, Oliver Zimmer, Ferenc Gl\"uck, Dennis Rich With the neutron decay spectrometer $a$SPECT we aim to measure the proton spectrum in free neutron beta decay precisely. This allows us to determine the neutrino electron correlation coefficient $a$. We had our first test beam time in 2005/06 at the new neutron source FRM-II in Garching. In my talk I want to talk about the results, the systematic effects we found and the ways how to deal with them in later beam times. [Preview Abstract] |
Friday, October 12, 2007 4:12PM - 4:24PM |
ED.00012: aCORN: An Experiment to Measure the Electron-Antineutrino Correlation in Neutron Decay A. Laptev, I. Stern, C. Trull, F.E. Wietfeldt, M. Leuschner, G. Noid, E. Stephenson, A. Komives, A. Beylor, B. Collett, G. Jones, D. Shapiro, F. Bateman, M.S. Dewey, B. Fisher, P. Mumm, J. Nico, A. Thompson, R. Wilson, B. Yerozolimsky, J. Byrne The angular correlation between the beta electron and antineutrino in free neutron beta decay is characterized by the dimensionless parameter $a$ which, when combined with other neutron decay parameters, can be used to determine the $g_{V}$ and $g_{A}$ constants and test the validity and self-consistency of the Standard Model. In the new experimental method employed by aCORN, an asymmetry proportional to $a$ is produced in the coincident detection of the electron and recoil proton. This approach has good potential for smaller systematic uncertainties, which are expected to be less than 1{\%} of $a$. After completion of the detailed design, the component construction and testing is in progress. It is expected that integration and a test run will start at the LENS of the IUCF in 2008. The entire aCORN apparatus will move to NIST for a physics run with a cold neutron beam in fall 2008. This project is supported by the National Science Foundation. [Preview Abstract] |
Friday, October 12, 2007 4:24PM - 4:36PM |
ED.00013: aCORN Backscatter-suppressing Electron Detector Carroll Trull A description and status report of the beta spectrometer for the upcoming experiment, \emph{aCORN}, will be presented. The experiment measures the electron-antineutrino correlation in neutron beta decay. Electron backscatter from the electron energy detector produces a low-energy tail that can cause a large systematic error in the experiment. The spectrometer is designed to veto more than 90\% of the backscattered electrons and measure the electron energy with a resolution of better than 20\%. A prototype was built and tested, and the final version has now been assembled. [Preview Abstract] |
Friday, October 12, 2007 4:36PM - 4:48PM |
ED.00014: The Electron Backscatter Background in the aCORN Experiment G.A. Noid, E.J. Stephenson aCORN is an experiment to measure $a$, the angular correlation between the anti-neutrino and the electron in neutron beta decay. We will use a row of collimators with a co-linear magnetic field to select events with the protons and electrons emerging from the decay region in opposite directions. A comparison of the relative rates for the two groups with the anti-neutrino momentum parallel or anti-parallel to the electron momentum yields an asymmetry which is easily related to $a$. Through simulations we discovered a large background associated with electrons backscattering off the proton detector region and then being detected by the beta spectrometer. By moving our proton detector off-axis, we hope to reduce this background to below our goal of less than a 1{\%} relative effect on the asymmetry while preserving 100{\%} collimated proton detection efficiency. [Preview Abstract] |
Friday, October 12, 2007 4:48PM - 5:00PM |
ED.00015: Dead layer measurements on diode detectors Areg Danagoulian, Libertad Barron-Palos, Andreas Klein, Scott Wilburn The goal of the abBA experiment involves coincidence measurements of protons and electrons from the neutron beta decay. While electron detection is rather straightforward, the detection of the protons is complicated due to their low energies. In order to understand the detector reponse and to determine the lower cut off value for the energy a technique for determining the thickness of the dead layer has been developed. A discussion of the measurement and of the results will be presented. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700