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 CD: Mini-Symposium on Fundamental Neutron Physics I |
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Chair: Shelley Page, University of Manitoba Room: Newport News Marriott at City Center Grand Salon IV |
Friday, October 12, 2007 9:00AM - 9:36AM |
CD.00001: Fundamental Neutron Physics: an Overview Invited Speaker: Experiments using neutrons have been used to refine our understanding of the weak interaction. These include measurements of neutron beta-decay observables and parity violating nucleon-nucleon interactions. Precision measurements using low energy neutrons are also useful in the search for new physics beyond the Standard Model. I will discuss some new and ongoing research in this field. [Preview Abstract] |
Friday, October 12, 2007 9:36AM - 9:48AM |
CD.00002: Status of the Fundamental Neutron Physics Beamline at the Spallation Neutron Source Geoffrey Greene, Vince Cianciolo, Richard Allen, Paul Huffman, W. Michael Snow, Takeyasu Ito The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory initiate operations in April 2006 and is in the process of ramping up to full operational capacity. The SNS has dedicated one of its cold neutron beamlines for nuclear and particle physics research. This Fundamental Neutron Physics Beamline (FNPB) is scheduled to commence operations in 2008. The anticipated research program at the FNPB includes studies of neutron beta decay and the hadronic weak interaction as well as a search for a neutron electric dipole moment. The talk will give an overview of the FNPB project, a construction status update, and a description of the initial, anticipated, suite of measurements. [Preview Abstract] |
Friday, October 12, 2007 9:48AM - 10:00AM |
CD.00003: ABSTRACT WITHDRAWN |
Friday, October 12, 2007 10:00AM - 10:12AM |
CD.00004: The NPDGamma Experiment; Data and Preliminary Results from the LANSCE phase Mikayel Dabaghyan The NPDGamma experiment is measuring the directional parity violating asymmetry in the emission of gamma rays from the capture of cold neutrons on protons. The asymmetry can be related in a straightforward way to effective couplings within an appropriate NN weak interaction theory, such as chiral perturbation based effective field theories. Since this is a measurement within a two body system, the observables are calculable without uncertainties from few to many body (large nuclei) effects. The experiment consists of two phases. The first one, at the Los Alamos Neutron Science Center (LANSCE), has just been completed, providing a measurement of the asymmetry to an accuracy at the 10$^{-7}$ level. The second phase of the experiment will commence at the Spallation Neutron Source at Oak Ridge, where it is currently being reassembled, to continue the measurement to an accuracy at the 10$^{-8}$ level. On behalf of the NPDGamma collaboration, I will present a brief overview of the LANSCE phase of the experiment, including the layout and a report on the data analysis and some preliminary results. [Preview Abstract] |
Friday, October 12, 2007 10:12AM - 10:24AM |
CD.00005: The NPDGamma Experiment at the SNS FnPB Christopher Crawford The NPDGamma experiment recently concluded a successful first phase data-taking run at LANSCE and is now moved to ORNL where it has been approved to run as the first experiment at the Fundamental Neutron Physics Beamline at the SNS. To accommodate the SNS beam and lessons learned at LANSCE, a number of changes have been proposed for the experiment. I will describe these improvements and upgrades, and the expected performance of the experiment to measure the parity-violating directional gamma asymmetry $A_\gamma$ of the reaction $\mbox{n} + \mbox{p} \to \mbox{d} + \gamma$ with an error of $1\times10^{-8}$. [Preview Abstract] |
Friday, October 12, 2007 10:24AM - 10:36AM |
CD.00006: The Parity Violating Longitudinal Asymmetry in the capture of Cold Neutrons on $^3$He. Michael Gericke, J. David Bowman, Christopher Crawford, Seppo Penttila, W. Michael Snow Within the framework of $\chi$PT based effective field theory models the nucleon-nucleon (NN) weak interaction is described in terms of various effective coupling constants, of which there are at least 4 but generally up to 15 without the application of cutoffs. There are few possible parity violating NN experiments that could constrain or test the predicted coupling strengths and they are often very challenging to implement. We have analyzed the feasibility of a new experiment which would measure the parity violating longitudinal asymmetry in cold neutron capture on an unpolarized $^3$He target. The great advantage of this experiment would be that there are only a handful of components needed and that these employ common, well known technologies without the need for lengthy R\&D. We will present a reference design and run time estimate as well as an analysis of systematic effects to show that this would be a feasible experiment which could run at the Spallation Neutron Source, Oak Ridge. [Preview Abstract] |
Friday, October 12, 2007 10:36AM - 10:48AM |
CD.00007: Measurement in progress of the parity-violating neutron spin-rotation in liquid $^4$He D.M. Markoff, C.D. Bass, J.M. Dawkins, T.D. Finley, J.C. Horton, C.R. Huffer, D. Luo, M.G. Sarsour, W.M. Snow, K. Gan, A.K. Opper, A.M. Micherdzinska, B.R. Heckel, H.E. Swanson, H.P. Mumm, J.S. Nico, B.E. Crawford, E.I. Sharapov As part of a program to characterize the low-energy, weak hadronic interaction, an experiment is in progress at the NIST Center for Neutron Research to measure the parity-violating neutron spin-rotation observable in the $n$-$\alpha$ system. The apparatus is designed to measure the rotation of the transverse polarization vector of long-wavelength neutrons as they traverse the helium target with a sensitivity of $3 \times 10^{-7}$ rad/m. To reach this goal, we have worked towards reducing systematic effects from background magnetic fields and neutron scattering and through understanding the apparatus and beam. We developed the helium target system to reduce the effects of neutron scattering and to increase operational reliability. We initiated a series of measurements in solid targets with known large or negligible parity-violating signals to study systematics from the polarimeter. The apparatus and experiment status will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:48AM - 11:00AM |
CD.00008: Proposed measurement of the neutron spin-rotation through solid ortho-deuterium. A. Komives, D.M. Markoff, B.J. Crowe In recent review papers [1,2] a program to study parity-violating (PV) nucleon-nucleon (NN) interaction observables including spin-rotation in the $\vec{n}$-$\alpha$ and $\vec{n}$-$p$ systems has been proposed to characterize the weak NN interaction. The rotation of the transverse neutron polarization vector as the long-wavelength neutron traverses the medium, results from the PV weak forward scattering amplitude. We propose that the spin-rotation observable in the $\vec{n}$-$d$ system would greatly contribute to this experimental and theoretical effort. Neutron depolarization from a relative large scattering cross section of a few barns in the deuterium could greatly dilute the small rotation signal on the order of $10^{-7}$ radians. Recent measurements were performed at the FUNSPIN beam line at the Paul Scherrer Institute of the depolarization of neutrons transmitted through liquid and solid ortho-deuterium as a function of neutron energy [3]. Results indicate that the observed depolarization of cold neutrons through solid ortho-deuterium is low enough for a measurement of the neutron spin-rotation to be feasible. We present here a proposed apparatus and program to measure the neutron spin-rotation in the $\vec{n}$-$d$ system.\newline [1] B. R. Holstein, {\it Nucl. Phys.} {\bf A737}:85-92 (2004).\newline [2] S.G. Page and M. Ramsey-Musolf, {\it Ann. Rev. Nucl. Part. Sci.} {\bf 56} (2006).\newline [3] A. Komives, {\it Bull. Am. Phys. Soc.} {\bf 51}, No. 6, HC.00008 (2006). [Preview Abstract] |
Friday, October 12, 2007 11:00AM - 11:12AM |
CD.00009: Measuring the Neutron Lifetime Using Magnetically Trapped Ultracold Neutrons Christopher O'Shaughnessy, Kevin Coakley, John Doyle, Robert Golub, Paul Huffman, Ekaterina Korobkina, Steve Lamoreaux, Hans Mumm, Karl Schelhammer, Pil-Neo Seo, Christopher Swank, Alan Thompson, Grace Yang, Liang Yang The neutron lifetime is an important parameter for tests of standard model and big bang nucleosynthesis. Our collaboration has successfully demonstrated the feasibility of using magnetically trapped ultracold neutrons for this measurement. In this experiment ultracold neutrons are loaded into an Ioffe-type superconducting magnetic trap as they are produced through the superthermal technique in superfluid helium-3. Trapped neutrons are then detected via scintillation light of liquid helium due to the decay events. The advantages of this technique are the continuous detection of the decay events and the elimination of trap losses due to interactions with a material wall potential. Current work is aimed at upgrading the experiment to include a larger and deeper magnetic trap. This is expected to reduce the statistical uncertainties to 1-3 s. Here the apparatus upgrades will be discussed. [Preview Abstract] |
Friday, October 12, 2007 11:12AM - 11:24AM |
CD.00010: Measuring the Spin-Dependent Scattering Length of $^{3}$He using Neutron Interferometry M. Huber, F.E. Wietfeldt, M. Arif, T.R. Gentile, W. Chen, D. Pushin, L. Lang, T. Black Experimental measurements of neutron scattering lengths are only recently achieving the required accuracy to test nucleon-nucleon (N-N) models. Neutron Interferometry (NI) provides some of the most precise values of spin-independent neutron scattering lengths including percent or better measurements for n-H, n-D, and n-$^{3}$He. For $^{3}$He, the spin-dependent neutron scattering length, b$_{i}$, has been measured once before by Zimmer \textit{et al}. [1] using a polarized $^{3}$He target inside a spin echo apparatus. Their result b$_{i}=-$2.365(20) differs from various theoretical models by more than 4$\sigma $. Currently, we are conducting an experiment to measure b$_{i}$ for $^{3}$He to better than half a percent at the NI and Optics Facility at the National Institute of Standards and Technology (NIST) using a small, flat-windowed gas cell containing polarized $^{3}$He. This is the first use of a polarized gas target in a NI. Results from this experiment will be presented. This work is supported by the National Science Foundation and NIST. \newline \newline [1] O. Zimmer \textit{et al}. Journal EPJ direct, 4(1):1--28, 2002. [Preview Abstract] |
Friday, October 12, 2007 11:24AM - 11:36AM |
CD.00011: An Apparatus for Absolute Neutron Flux Measurement A. Yue, G. Greene, M.S. Dewey, D. Gilliam, J. Nico, A. Laptev A fully-absorbing neutron detector is being developed to measure the absolute flux (s$^{-1}$) of a cold neutron beam at the level of 0.1\,\%. The device will be used to calibrate a neutron flux monitor used in an in-beam neutron lifetime measurement performed at NIST ($\tau_{n} = \left(886.3 \pm 3.4\right)$ s). The precision of the measurement was limited by the uncertainty in the efficiency of the neutron flux monitor (0.3\,\%). The flux monitor operates by counting charged particles produced when neutrons impinge on a ${}^{6}$Li (or ${}^{10}$B) foil. Its efficiency was calculated from the cross section, the solid angle subtended by the charged particle detectors, and the amount of neutron-absorbing material present on the foil. Successful calibration would reduce the neutron lifetime uncertainty to approximately 0.25\,\%. In addition, using the measured solid angle and amount of material on the deposit, a new experimental value for the ${}^{6}$Li or (${}^{10}$B) capture cross section will be obtained. Details of the apparatus and the measurement technique along with the status of the experiment will be discussed. [Preview Abstract] |
Friday, October 12, 2007 11:36AM - 11:48AM |
CD.00012: Precision Polarimetry for Cold Neutrons Libertad Barron-Palos, J. David Bowman, Timothy E. Chupp, Christopher Crawford, Areg Danagoulian, Thomas R. Gentile, Gordon Jones, Andreas Klein, Seppo I. Penttila, Americo Salas-Bacci, Monisha Sharma, W. Scott Wilburn The abBA and PANDA experiments, currently under development, aim to measure the correlation coefficients in the polarized free neutron beta decay at the FnPB in SNS. The polarization of the neutron beam, polarized with a $^3$He spin filter, has to be known with high precision in order to achieve the goal accuracy of these experiments. In the NPDGamma experiment, where a $^3$He spin filter was used, it was observed that backgrounds play an important role in the precision to which the polarization can be determined. An experiment that focuses in the reduction of background sources to establish techniques and find the upper limit for the polarization accuracy with these spin filters is currently in progress at LANSCE. A description of the measurement and results will be presented. [Preview Abstract] |
Friday, October 12, 2007 11:48AM - 12:00PM |
CD.00013: A Study of the Effect of Neutron Beam on $^{3}$He Spin Filters Monisha Sharma, Libertad Barron-Palos, Timothy E. Chupp, Christopher Crawford, Areg Danagoulian, Thomas R. Gentile, Gordon Jones, Andreas Klein, Bernhard Lauss, Seppo I. Penttila, Todd B. Smith, Eric Tardiff, W. Scott Wilburn A polarized $^{3}$He neutron spin filter has been used for the NPDGamma experiment at the FP12 beamline at LANSCE. During the experiment we observed a new, but currently unexplained effect of the neutron beam on the $^{3}$He polarization, leading to reductions of the $^{3}$He polarization of several percent. This effect is consistent with a rapid reduction of the average rubidium polarization, but could also be due to a reduction of the $^{3}$He relaxation rate. It is not known how the effect scales with neutron flux or flux density. Systematic studies of Rb and $^{3}$He polarization in the neutron beam are currently underway at LANSCE and the progress towards the understanding of this effect will be reported. [Preview Abstract] |
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