122047411
The BLAST experiment
The Bates large acceptance spectrometer toroid (BLAST) experiment was operated at the MIT-Bates Linear Accelerator Center from 2003 until 2005. The detector and experimental program were designed to study, in a systematic manner, the spin-dependent electromagnetic interaction in few-nucleon systems. As such the data will provide improved measurements for neutron, proton, and deuteron form factors. The data will also allow details of the reaction mechanism, such as the role of final state interactions, pion production, and resonances to be studied. The experiment used: a longitudinally polarized electron beam stored in the South Hall Storage Ring; a highly polarized, isotopically pure, internal gas target of hydrogen or deuterium provided by an atomic beam source; and a symmetric, general purpose detector based on a toroidal spectrometer with tracking, time-of-flight, Cherenkov, and neutron detectors. Details of the experiment and operation are presented.
97662300
MEASUREMENT OF THE PROTON ELECTROMAGNETIC FORM FACTOR RATIO AT BLAST
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.
5587472
Role of mesons in the electromagnetic form factors of the nucleon
The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q 2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q 2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as “charge distributions,” nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment‐theory comparisons.
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
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.
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.