Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved ...dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.
A magnetic coil operated at cryogenic temperatures is used to produce spatial, relative field gradients below 6ppm/cm, stable for several hours. The apparatus is a prototype of the magnetic ...components for a neutron electric dipole moment (nEDM) search, which will take place at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory using ultra-cold neutrons (UCN). That search requires a uniform magnetic field to mitigate systematic effects and obtain long polarization lifetimes for neutron spin precession measurements. This paper details upgrades to a previously described apparatus 1, particularly the introduction of super-conducting magnetic shielding and the associated cryogenic apparatus. The magnetic gradients observed are sufficiently low for the nEDM search at SNS.
A precise measurement of the neutron decay β asymmetry A₀ has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science ...Center. Combining data obtained in 2008 and 2009, we report A₀ = -0.119 66±0.000 89{-0.001 40}{+0.001 23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275 90{-0.004 45}{+0.004 09}.
Geometric-phase-induced false electric dipole moment (EDM) signals, resulting from interference between magnetic field gradients and particle motion in electric fields, have been studied extensively ...in the literature, especially for neutron EDM experiments utilizing stored ultracold neutrons and co-magnetometer atoms. Previous studies have considered particle motion in the transverse plane perpendicular to the direction of the applied electric and magnetic fields. We show, via Monte Carlo studies, that motion along the field direction can impact the magnitude of this false EDM signal if the wall surfaces are rough such that the wall collisions can be modeled as diffuse, with the results dependent on the size of the storage cell's dimension along the field direction.
We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta ...(e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.
High uniformity magnetic coil for search of neutron electric dipole moment Pérez Galván, A.; Plaster, B.; Boissevain, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2011, Volume:
660, Issue:
1
Journal Article
Peer reviewed
We present in this article a prototype magnetic coil that has been developed for a new search for the electric dipole moment of the neutron at the Spallation Neutron Source at Oak Ridge National ...Laboratory. The gradients of the magnetic field generated by the coil have been optimized to reduce known systematic effects and to yield long polarization lifetimes of the trapped particles sampling the highly uniform magnetic field. Measurements of the field uniformity of this prototype magnetic coil are also presented.
A significant challenge for experiments requiring a highly uniform magnetic field concerns the identification and design of a discretized and finite-sized magnetic field coil of minimal size. In this ...work we compare calculations of the magnetic field uniformities and field gradients for three different standard (i.e., non-optimized) types of coils: cosθ, solenoidal, and spherical coils. For an experiment with a particular requirement on either the field uniformity or the field gradient, we show that the volume required by a spherical coil form which satisfies these requirements can be significantly less than the volumes required by cosθ and solenoidal coil forms.
The Nab experiment will measure the correlation a between the momenta of the beta particle and antineutrino in neutron decay as well as the Fierz term b which distorts the beta spectrum.
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