7198768
Measurement of parity-violating γ-ray asymmetry in the capture of polarized cold neutrons on protons
The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry A{sub {gamma}} with respect to the neutron spin direction of {gamma} rays emitted in the reaction n + p {yields} d + {gamma} using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction between nucleons to be induced by the weak interaction between quarks. A{sub {gamma}} in n + p {yields} d + {gamma} is dominated by a {Delta}I = 1, {sup 3}S{sub 1-}{sup 3}P{sub 1} parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE), with the result A{sub {gamma}} = [-1.2 {+-} 2.1 (stat.) {+-} 0.2 (sys.)] x 10{sup -7}. We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result A{sub {gamma}LR} = [-1.8 {+-} 1.9 (stat.) {+-} 0.2 (sys.)] x 10{sup -7}. In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, andmore » LANSCE results. The asymmetry has an estimated size of 5 x 10{sup -8} and the aim of the NPDGamma collaboration is to measure it to 1 x 10{sup -8}. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.« less
906060
Neutron charge radius and the neutron electric form factor
For nearly forty years, the Galster parametrization has been employed to fit existing data for the neutron electric form factor, G{sub E}{sup n}, vs the square of the four-momentum transfer, Q{sup 2}. Typically this parametrization is constrained to be consistent with experimental data for the neutron charge radius. However, we find that the Galster form does not have sufficient freedom to accommodate reasonable values of the radius without constraining or compromising the fit. In addition, the G{sub E}{sup n} data are now at sufficient precision to motivate a two-parameter fit (or three parameters if we include thermal neutron data). Here we present a modified form of a two-dipole parametrization that allows this freedom and fits both G{sub E}{sup n} (including recent data at both low and high four-momentum transfer) and the charge radius well with simple, well-defined parameters. Analysis reveals that the Galster form is essentially a two-parameter approximation to the two-dipole form but becomes degenerate if we try to extend it naturally to three parameters.
120228855
A measurement of correlation parameters in the decay of polarized free neutrons: The abBA experiment
The abBA experiment will measure, in the same apparatus, four correlation parameters in the free neutron ?-decay: the electron-antineutrino angular correlation (a), the Fierz interference term (6), and the asymmetries, with respect to the neutron spin direction, of the electron (A)and antineutrino (B).The precise determination of these parameters, together with the neutron lifetime, will provide important information about the Standard Model (SM) and will establish constraints for new physics. In this paper we describe the experimental methodology of abBA as well as some of the advances that have been done so far.
14179221
Nab: Measurement principles, apparatus and uncertainties
Abstract The Nab collaboration will perform a precise measurement of a , the electron–neutrino correlation parameter, and b , the Fierz interference term in neutron beta decay, in the Fundamental Neutron Physics Beamline at the SNS, using a novel electric/magnetic field spectrometer and detector design. The experiment is aiming at the 10 - 3 accuracy level in Δ a / a , and will provide an independent measurement of λ = G A / G V , the ratio of axial-vector to vector coupling constants of the nucleon. Nab also plans to perform the first ever measurement of b in neutron decay, which will provide an independent limit on the tensor weak coupling.
12583573
Optimization of the ballistic guide design for the SNS FNPB 8.9 Å neutron line
Abstract The optimization of the ballistic guide design for the SNS Fundamental Neutron Physics Beamline 8.9 A line is described. With a careful tuning of the shape of the curve for the tapered section and the width of the straight section, this optimization resulted in more than a 75% increase in the neutron flux exiting the 33 m long guide over a straight m = 3.5 guide with the same length.
96460330
High-efficiency resonant rf spin rotator with broad phase space acceptance for pulsed polarized cold neutron beams
High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPD Gamma experiment, a search for the small parity-violating {gamma}-ray asymmetry A{sub Y} in polarized cold neutron capture on parahydrogen, is one example. For the NPD Gamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized {sup 3}He neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 {+-} 0.5% for neutron energies from 3 to 20 meV over the full phasemore » space of the beam. Systematic effects that the rf spin rotator introduces to the NPD Gamma experiment are considered.« less
5102800
Fermilab electron cooling project: field measurements in the cooling section solenoid
To provide the maximum possible cooling rate for the Recycler Electron Cooling (REC), the cooling section has to be immersed into a high-quality longitudinal magnetic field. Namely, the solenoidal field of 50-150 G should have an integral of the transverse component below 1 G-cm over the whole 20-m cooling section. The transverse field components are measured by a dedicated compass-based sensor, which has been designed and manufactured at Budker INP, Novosibirsk. The paper describes results of the field measurements performed on the cooling section solenoid prototypes as well as the design and the calibration procedure of the sensor.