Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session DE: Electroweak Interactions II |
Hide Abstracts |
Chair: Volker Crede, Florida State University Room: Coronado |
Thursday, November 4, 2010 10:30AM - 10:42AM |
DE.00001: aCORN:-the electron-neutrino correlation coefficient in free neutron decay Brian Collett The decay of the free neutron provides a testing ground for the Standard Model without complications from nuclear structure. The electron-antineutrino angular correlation coefficient, $a$, is the least well determined of the angular correlation coefficients that have been precisely measured. An improved measurement of $a$ will refine the value of the axial-vector coupling constant. This may help resolve discrepancies left by recent measurements of A and the neutron lifetime. The aCORN experiment aims to measure $a$ to a relative accuracy of $<$1{\%} using a novel method that does not depend on precise measurement of proton recoil energy. The apparatus features electron and proton detectors placed at opposite ends of a 3m long vacuum vessel in an axial magnetic field. An electrostatic mirror around the decay region directs protons to the proton detector in two populations, distinguished by time of flight. The value of $a$ is proportional to the asymmetry between the populations. The experiment will run at NIST through March 2011. An overview of the method and experiment design will be presented, followed by three talks on details of the experiment. [Preview Abstract] |
Thursday, November 4, 2010 10:42AM - 10:54AM |
DE.00002: The aCORN Magnetic Field and Collimation Systems George Noid The aCORN instrument's sensitivity to the electron-anti neutrino correlation in neutron decay depends on measuring the counting asymmetry between two kinematically distinct groups of decay events. This asymmetry is proportional to the correlation parameter ``a''. Decay particles are selected by a highly uniform axial magnetic field and a series of tungsten apertures. An electrostatic mirror reflects all protons toward the proton detector. Misalignment of the collimator axis to the magnetic field axis, internal misalignment of the collimators, and transverse components of the magnetic field can all result in a false counting asymmetry between the two groups. Alignment of the collimator assembly and trimming to the design magnetic field will be presented. [Preview Abstract] |
Thursday, November 4, 2010 10:54AM - 11:06AM |
DE.00003: The aCORN Beta spectrometer Guillaume Darius In order to measure the electron-antineutrino correlation parameter in neutron decay, the aCORN experiment requires a detector capable of detecting with high efficiency the beta electrons produced and measuring their energies. This is done using a single plastic scintillator coupled to 19 photomultiplier tubes. An array of eight plastic scintillators surrounds the energy detector to veto events where the electrons are backscattered. If kept, these events would lead to a large systematic error and must be removed from the data. The veto scintillators surround an electron beam that diverges in a weakening magnetic field so as to increase the probability that backscattered electrons encounter them. A description of the detector and tests results will be presented. [Preview Abstract] |
Thursday, November 4, 2010 11:06AM - 11:18AM |
DE.00004: The aCORN Proton Detector System Alexander Komives The method used by the aCORN collaboration to produce a precise measurement of the electron-antineutrino correlation from neutron beta decay requires a detector capable of counting the low energy, less than 750 eV, recoil protons. These protons are selected by a series of tungsten apertures and an axial magnetic field. Protons in the ``fast'' and ``slow'' groups, corresponding to antineutrinos moving parallel and anti- parallel to the electron momenta respectively, must be counted with equal efficiency. Additional provisions are needed to prevent electrons that travel to the proton detector region from being reflected to the electron detector at the opposite end of the apparatus. A system has been designed and built to satisfy these criteria and has been operationally tested. Details of the detector system and test results will be presented. [Preview Abstract] |
Thursday, November 4, 2010 11:18AM - 11:30AM |
DE.00005: Polarimetry Measurements for the NPDGamma Experiment Matthew Musgrave The NPDGamma experiment intends to measure the parity violating directional asymmetry in the angular distribution of gamma rays in the capture of polarized neutrons on protons. The asymmetry is sensitive to the weak nucleon-nucleon interaction, and the largest contribution to the asymmetry comes from weak pion exchange. The capture of polarized neutrons on protons is a two nucleon system which will provide a measurement of the weak pion-nucleon coupling. The precision of the measurement is dependent on how well the polarization of the neutron beam is known. The neutrons are polarized with a supermirror polarizer, and the polarization will be measured with a polarized 3He spin filter for different directional neutron polarizations set with a resonant rf spin rotator. The technique to determine the polarimetry as well as simulated results will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 11:30AM - 11:42AM |
DE.00006: The NPDGamma experiment - A measurement of parity violation in polarized cold neutron capture Nadia Fomin The NPDGamma experiment aims to measure the correlation between the neutron spin and the direction of the emitted photon in neutron-proton capture. An up-down parity violating asymmetry from this process can be directly related to the strength of the hadronic weak interaction between nucleons. The first phase of the experiment was completed in 2006 at LANSCE. The methodology will be discussed and preliminary results will be presented. The next run will start in late 2010 at the SNS at ORNL with several improvements, which will be discussed. The upcoming run will yield a measurement with a projected statistical error 1$\times$10$^{-8}$. This will finally allow the result to be compared with theoretical predictions. [Preview Abstract] |
Thursday, November 4, 2010 11:42AM - 11:54AM |
DE.00007: The parity-violating asymmetry in the $^3$He($\vec{n},p$)$^3$H reaction Michele Viviani In this contribution, we report for a theoretical study of the longitudinal asymmetry induced by parity-violating (PV) nucleon-nucleon potential in the charge-exchange reaction $^3$He($\vec{n},p$)$^3$H. Such an experiment is in an advanced stage of planning at the Spallation Neutron Source at Oak Ridge National Laboratory. The matrix elements involving PV transitions are obtained in first-order perturbation theory in the hadronic weak-interaction potential, while those connecting states of the same parity are derived from solutions of the strong-interaction Hamiltonian with the hyperspherical-harmonics (HH) method, fully accounting for the coupled-channel nature of the scattering problem. We also present predictions for the n-${}^3$He scattering lengths and compare them with the available measured values. The longitudinally asymmetry is finally calculated for vanishing neutron incident energies, in correspondence of two models of PV nucleon-nucleon interaction, the so-called DDH potential, and the one derived in pionless EFT. [Preview Abstract] |
Thursday, November 4, 2010 11:54AM - 12:06PM |
DE.00008: Parity violation in $n + ^3He \rightarrow ^3H + p$ reaction: resonance approach Vladimir Gudkov The method based on microscopic theory of nuclear reactions has been applied for analysis of parity violating effects in a few- body systems. Different parity violating and parity conserving asymmetries and their dependence on neutron energy have been estimated for $n + ^3He \rightarrow ^3H + p$ reaction. The estimated effects are in a good agreement with available exact calculations. [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