Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session NF: NPDGamma and nd Reactions |
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Chair: Werner Tornow, Duke University Room: Garden III |
Saturday, October 27, 2012 8:30AM - 8:42AM |
NF.00001: An Overview of the NPDGamma Experiment Elise Martin The NPDGamma Experiment uses the parity violation in gamma-ray emission from polarized cold neutron capture on protons to measure the strength of the weak nucleon-nucleon interaction. In the meson exchange picture, this reaction is dominated by pion exchange. Recently, we completed the first successful data production cycle at the Spallation Neutron Source at ORNL. I will present an overview of the NPDGamma experiment, including the motivation for the work, the apparatus, methodology, issues encountered during the measurement, and recent data taken. [Preview Abstract] |
Saturday, October 27, 2012 8:42AM - 8:54AM |
NF.00002: First results from the NPDGamma Experiment at the Spallation Neutron Source Nadia Fomin The NPDGamma experiment aims to measure the parity-odd correlation between the neutron spin and the direction of the emitted photon in cold neutron-proton capture. A parity violating asymmetry (to be measured to 10$^{-8}$) from this process can be directly related to the strength of the hadronic weak interaction between nucleons, specifically the $\Delta I=1$ contribution. As part of the commissioning runs on the Fundamental Neutron Physics beam line at the Spallation Neutron Source at ORNL, the gamma-ray asymmetries from the parity-violating capture of cold neutrons on $^{35}$Cl and $^{27}$Al were measured, to check for systematic effects, false asymmetries, and backgrounds. Early this year, the parahydrogen target for the production run of NPDGamma was commissioned. Results of commissioning measurements will be reviewed and first hydrogen data will be shown. [Preview Abstract] |
Saturday, October 27, 2012 8:54AM - 9:06AM |
NF.00003: Neutron Polarization Measurements with a 3He Spin Filter for the NPDGamma Experiment Matthew Musgrave The Fundamental Neutron Physics Beamline (FNPB) at the Spallation Neutron Source (SNS) provides a pulsed beam of polarized cold neutrons for the NPDGamma experiment which intends to measure the parity violating asymmetry in the emitted gamma rays from the capture of polarized neutrons on protons in a para-hydrogen target. The neutrons are polarized by a multi-channel super mirror polarizer, and the polarization of each neutron pulse can be flipped with an RF spin rotator. The accuracy of the NPDGamma experiment and various commissioning experiments is dependent on the polarization of the neutron beam and the efficiency of the RF spin rotator. These parameters are measured with a polarized 3He spin filter at multiple points in the beam cross section and with multiple 3He polarizations. The measured neutron polarization is compared to a McStas model to validate our results and our beam averaging technique. The analysis methods, background effects, and results will be discussed. [Preview Abstract] |
Saturday, October 27, 2012 9:06AM - 9:18AM |
NF.00004: The liquid parahydrogen target of the NPDGamma Experiment Zhaowen Tang The NPDGamma Experiment completed in June of 2012 at the Spallation Neutron Source its first run cycle dedicated to measurement of the parity-violating correlation $A_\gamma$ between neutron spin and gamma momentum in the reaction $\overrightarrow{n} + p\rightarrow d + \gamma$. In our measurement, a polarized cold neutron beam is captured on a 16 liter liquid parahydrogen target. We will describe the performance of the target system which has run steadily and reliably for four months since February. [Preview Abstract] |
Saturday, October 27, 2012 9:18AM - 9:30AM |
NF.00005: Backgrounds in the NPDGamma Experiment Serpil Kucuker Dogan The NPDGamma experiment, which measures the parity-violating directional gamma asymmetry in neutron-proton capture, completed its first run cycle in June at the Fundamental Neutron Physics Beamline at the Oak Ridge Spallation Neutron Source. In the experiment intense polarized low-energy neutron beam interacts with liquid para-hydrogen target. Gamma rays from the capture reaction are detected by 48 CsI(Tl) detectors with the 3$\pi$ acceptance angle. The goal of the experiment is to measure the asymmetry with precision of $1 \times 10^{-8}$. The polarized neutrons also interact with other materials in the beam windows and the walls of the target vessel producing a background to the signal that dilutes the PV gamma asymmetry and these materials (primarily Aluminum) could, in principle, have their own PV asymmetries. Therefore, it is important to study the backgrounds and their contributions to measured signals. I will discuss the detected backgrounds and their effect on NPDGamma. [Preview Abstract] |
Saturday, October 27, 2012 9:30AM - 9:42AM |
NF.00006: Parahydrogen Fraction in a Liquid Hydrogen target in the NPDGamma Experiment Chad Gillis The NPDGamma Experiment at SNS is measuring $A_\gamma$, the directional $\gamma$ asymmetry in polarized cold neutron capture on parahydrogen, with a statistics-limited precision of $1 \times 10^{-8}$. One of the parameters that affect the measured asymmetry is the polarization of the neutron beam upon capture. The depolarization of a neutron beam of under 15 meV in liquid hydrogen arises due to the large spin flip scattering cross section of orthohydrogen. We have set up beam monitors before and after the hydrogen target to measure the relative transmissions of the target in the empty and full configurations. The extracted orthohydrogen concentration can be modeled to deduce a depolarization upon capture. I will present an upper bound estimate of the depolarization upon capture during the first run cycle that was recently completed. [Preview Abstract] |
Saturday, October 27, 2012 9:42AM - 9:54AM |
NF.00007: Symmetry violations in neutron-deuteron reactions Vladimir Gudkov, Young-Ho Song, Rimantas Lazauskas The study of parity violating (PV) and time reversal invariance violating (TRIV) effects in low energy physics are very important for the understanding of the main features of the Standard model and for a search for the possible manifestations of new physics. In this talk we present a comprehensive analysis of PV and TRIV effects for the simple nuclear processes: neutron-deuteron reactions. We compare different PV and TRIV effects, which have been calculated using both traditional (DDH-type) symmetry violating potentials and the potentials obtained using the effective field theory approach. The possibility to measure symmetry violating effects in neutron-deuteron system and the issues related to theoretical uncertainties in calculations of these effects are discussed. [Preview Abstract] |
Saturday, October 27, 2012 9:54AM - 10:06AM |
NF.00008: ABSTRACT WITHDRAWN |
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