Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session PG: Neutrons II |
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Chair: Paul Huffman, North Carolina State University Room: Pearl Ballroom II |
Saturday, October 26, 2013 10:30AM - 10:42AM |
PG.00001: Parity Violation of Polarized Neutron Capture in $^{27}Al$ Zhaowen Tang The NPDGamma experiment measures the parity-odd asymmetry of outgoing gammas from polarized neutron capture on liquid para-hydrogen. Neutron capture on the aluminum vessel used to safely contain the liquid para-hydrogen contributes about $20\%$ of the total signal in the gamma detectors. A separate experiment was performed to determine the parity-violating gamma asymmetry in $^{27}Al$. I will present the analysis method and preliminary results. [Preview Abstract] |
Saturday, October 26, 2013 10:42AM - 10:54AM |
PG.00002: A data selection and reduction for asymmetry analysis in the NPDGamma experiment David Blyth The NPDGamma experiment intends to measure the parity-violating asymmetry in the direction of emitted photons from the capture of cold, polarized neutrons on protons. The $np \rightarrow d\gamma$ reaction is dominated by $\Delta I = 1$ transitions, and the asymmetry can be unambiguously related to corresponding contributions of the hadronic weak interaction. The experiment is currently operated at the Fundamental Neutron Physics Beamline (FNPB) of the Spallation Neutron Source at ORNL with the ultimate goal of a $10^{-8}$ measurement of the asymmetry. As an initial data selection technique for one of the parallel analyses of final data being taken by NPDGamma, a linear correlation method applied to beam intensity monitors is developed and implemented to remove irregular conditions of the pulsed 60 Hz cold neutron beam provided by the FNPB. A method for reduction of the asymmetry data will also be presented with the goal of minimizing statistical uncertainty due to beam and detector-gain fluctuations. [Preview Abstract] |
Saturday, October 26, 2013 10:54AM - 11:06AM |
PG.00003: A Measurement of the Total Cross Section of Liquid Parahydrogen for Cold Neutrons Kyle Grammer Liquid hydrogen is commonly used as a neutron moderator and accurate knowledge of the scattering cross section is critical for the design of cold sources. The total cross section for cold neutrons with wavelengths between 2.3 and 14{\AA} has been measured for liquid hydrogen at 15.7K. Provided that the orthohydrogen concentration [2] in the target vessel is at the thermodynamic equilibrium limit and using the known hydrogen absorption cross section, we can extract the parahydrogen scattering cross section from our measurement. Our result does not agree with the Seiffert [1] measurement and this disagreement cannot be due to orthohydrogen contamination in our measurement. The measurement was performed on the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at Oak Ridge National Laboratory. The experiment and data analysis will be described. \\[4pt] [1] W. D. Seiffert. Euratom Report No. EUR 4455d, 1970.\\[0pt] [2] See talk by R. C. Gillis. DNP October 2013. [Preview Abstract] |
Saturday, October 26, 2013 11:06AM - 11:18AM |
PG.00004: Systematic Effects in the Measurement of ``a'' with the aCORN Apparatus Alexander Komives Systematic effects that might cause an error in the measurement of ``a'', the electron-antineutrino correlation from free neutron decay, with the aCORN apparatus will be discussed. Because the experiment is dependent on both electron and proton detection, anything that can alter the motion of either particle is being examined. Among the effects discussed will be non-uniform magnetic and electric fields, residual gas in the vacuum chamber, the focusing efficiency of the proton detector system, the veto efficiency of backscattered electrons in the beta spectrometer, and the detection of scattered electrons. Ancillary measurements and simulations will be presented to characterize the sensitivity of ``a'' to these effects. [Preview Abstract] |
Saturday, October 26, 2013 11:18AM - 11:30AM |
PG.00005: Proton detection at aCORN Ed Stephenson, Melanie Novak The aCORN experiment will measure the electron-antineutrino angular correlation parameter in neutron beta-decay. Our method relies on proton time-of-flight information and electron spectroscopy. This presentation will focus on proton transport and detection. When neutrons decay inside our fiducial volume, emitted protons are directed to the top of the apparatus by an electrostatic mirror, which also pre-accelerates them. A uniform axial magnetic field then guides protons with low transverse momentum through a set of circular apertures. The protons are then accelerated towards a cooled silicon surface barrier detector by a high voltage focusing system, which boosts their energy to a detectable level, ensures they hit the active region of the detector, and deflects incoming electrons. The silicon detector is located off-axis to further minimize electron scattering. Our current design ensures high voltage stability; corona and sparking are reduced with better geometry and a locally lower magnetic field. A new dovetail support structure and separate reference jig allows easy installation with reproducible electrode positioning. Our silicon detector preamp was redesigned from the ground up to minimize noise, improve gain, and operate reliably in the aCORN environment. [Preview Abstract] |
Saturday, October 26, 2013 11:30AM - 11:42AM |
PG.00006: aCORN Beta Spectrometer and Electrostatic Mirror Md Hassan aCORN uses a high efficiency backscatter suppressed beta spectrometer to measure the electron-antineutrino correlation in neutron beta decay. We measure the correlation by counting protons and beta electrons in coincidence with precisely determined electron energy. There are 19 photomultiplier tubes arranged in a hexagonal array coupled to a single phosphor doped polystyrene scintillator. The magnetic field is shaped so that electrons that backscatter without depositing their full energy strike a tulip-shaped array of scintillator paddles and these events are vetoed. The detailed construction, performance and calibration of this beta spectrometer will be presented. I will also present the simulation, construction, and features of our novel electrostatic mirror. [Preview Abstract] |
Saturday, October 26, 2013 11:42AM - 11:54AM |
PG.00007: Magnetic field uniformity for the nEDM experiment Simon Slutsky The nEDM experiment at the Spallation Neutron Source (SNS) will search for a neutron electric dipole moment (EDM) with a sensitivity of $<5 \cdot10^{-28}$ e-cm. Neutrons will precess in a constant magnetic field and variable electric field, and non-zero neutron EDM will appear as a variation in the precession frequency. Gradients in the magnetic field lead to spurious EDM signals through a geometric phase effect. The volume averaged magnetic gradient must be below 0.1 $\mu$G/cm to reach the desired sensitivity. In this talk, we describe an effort to produce such a uniform magnetic field in a laboratory using a $\cos(\theta$) coil operated at cryogenic temperatures inside a superconducting lead shield. [Preview Abstract] |
Saturday, October 26, 2013 11:54AM - 12:06PM |
PG.00008: The cos-theta coil re-re-visited Christopher Crawford Precision measurement of symmetry violating effects such the electric dipole moment (EDM) of fundamental particles requires extremely uniform fields. The cos-theta coil is the standard workhorse for generating uniform transverse magnetic fields in these experiments. Limitations in field uniformity include fringe effects (finite length), discretization (finite number of wires), and construction tolerance (finite resources). The field can be isolated from its environment by superposition of two coaxial cos-theta coils of different radii and opposite magnetic moment (double-cos-theta coil), or by shielding the coil inside a permeable or superconducting cylinder. I will discuss methods for optimizing the field uniformity of a compact cos-theta coil, and compare the ultimate limit on errors due to each source described above. Within the context of the scalar potential, I will show a straightforward generalization to non-circular coils with $z$- or $\phi$-symmetry. [Preview Abstract] |
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