Heliospheric Images of the Solar Wind at Earth Sheeley, Jr., N. R; Herbst, A. D; Palatchi, C. A ...
The Astrophysical journal,
03/2008, Letnik:
675, Številka:
1
Journal Article, Web Resource
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During relatively quiet solar conditions throughout the spring and summer of 2007, the SECCHI HI2 white-light telescope on the STEREO B solar- orbiting spacecraft observed a succession of wave fronts ...sweeping past Earth. We have compared these heliospheric images with in situ plasma and magnetic field measurements obtained by near-Earth spacecraft, and we have found a near perfect association between the occurrence of these waves and the arrival of density enhancements at the leading edges of high-speed solar wind streams. Virtually all of the strong corotating interaction regions are accompanied by large-scale waves, and the low-density regions between them lack such waves. Because the Sun was dominated by long-lived coronal holes and recurrent solar wind streams during this interval, there is little doubt that we have been observing the compression regions that are formed at low latitude as solar rotation causes the high-speed wind from coronal holes to run into lower speed wind ahead of it.
The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively ...straightforward, the lack of a free neutron target makes measurements of the neutron's electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei ^{3}H and ^{3}He, where the nuclear effects are larger than for deuterium but expected to largely cancel in the cross-section ratios. We extracted values of the neutron magnetic form factor for low-to-modest momentum transfer, 0.6<Q^{2}<2.9 GeV^{2}, where existing measurements give inconsistent results. The precision and Q^{2} range of these data allow for a better understanding of the current world's data and suggest a path toward further improvement of our overall understanding of the neutron's magnetic form factor.
The SECCHI HI2 white-light imagers on the STEREO A and B spacecraft show systematically different proper motions of material moving outward from the Sun in front of high-speed solar wind streams from ...coronal holes. As a group of ejections enters the eastern (A) field of view, the elements at the rear of the group appear to overrun the elements at the front. (This is a projection effect and does not mean that the different elements actually merge.) The opposite is true in the western (B) field; the elements at the front of the group appear to run away from the elements at the rear. Elongation/time maps show this effect as a characteristic grouping of the tracks of motion into convergent patterns in the east and divergent patterns in the west, consistent with ejections from a single longitude on the rotating Sun. Evidently, we are observing segments of the "garden-hose" spiral made visible when fast wind from a low-latitude coronal hole compresses blobs of streamer material being shed at the leading edge of the hole.
We report on the first Q^{2}-dependent measurement of the beam-normal single spin asymmetry A_{n} in the elastic scattering of 570 MeV vertically polarized electrons off ^{12}C. We cover the Q^{2} ...range between 0.02 and 0.05 GeV^{2}/c^{2} and determine A_{n} at four different Q^{2} values. The experimental results are compared to a theoretical calculation that relates A_{n} to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the Q^{2} behavior of A_{n} given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.
Here we report a high precision measurement of electron beam polarization using Compton polarimetry. The measurement was made in experimental Hall A at Jefferson Lab during the CREX experiment in ...2020. A precision of dP/P = 0.36% was achieved detecting the back-scattered photons from the Compton scattering process. This is the highest precision in a measurement of electron beam polarization using Compton scattering ever reported, surpassing the ground-breaking measurement from the SLD Compton polarimeter. Such precision reaches the level required for the future flagship measurements to be made by the MOLLER and SoLID Experiments.
Parity-violating electron-scattering experiments represent an important focus of the nuclear physics experimental program at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson ...Lab. These experiments pose significant challenges because the scattering asymmetries can be very small, of the order parts-per-million and smaller. To succeed, the properties of the electron beam such as current, position, size and energy, must be very nearly identical in the two electron-polarization spin states (parallel and anti-parallel relative to the direction of beam motion at the scattering target). This paper describes the origins of unwanted helicity-correlated beam asymmetries present on the electron beam and methods to minimize them to acceptable levels.
Parity-violating electron-scattering experiments represent an important focus of the nuclear physics experimental program at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson ...Lab. These experiments pose significant challenges because the scattering asymmetries can be very small, of the order parts-per-million and smaller. To succeed, the properties of the electron beam such as current, position, size and energy, must be very nearly identical in the two electron-polarization spin states (parallel and anti-parallel relative to the direction of beam motion at the scattering target). This paper describes the origins of unwanted helicity-correlated beam asymmetries present on the electron beam and methods to minimize them to acceptable levels.
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