Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave ...function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep→e′pω, at central Q2 values of 1.60, 2.45 GeV2, at W=2.21 GeV. The results of our pioneering −u≈−umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q2=2.45 GeV2, the observed dominance of σT over σL, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.
We report a new determination of the strange quark contribution to the proton's magnetic form factor at a four-momentum transfer Q2=0.1 (GeV/c)2 from parity-violating e–p elastic scattering. The ...result uses a revised analysis of data from the SAMPLE experiment which was carried out at the MIT-Bates Laboratory. The data are combined with a calculation of the proton's axial form factor GeA to determine the strange form factor GsM(Q2=0.1)=0.37±0.20±0.26±0.07. The extrapolation of GsM to its Q2=0 limit and comparison with calculations is also discussed.
Fast neutron detection with a segmented spectrometer Langford, T.J.; Bass, C.D.; Beise, E.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2015, Letnik:
771
Journal Article
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A fast neutron spectrometer consisting of segmented plastic scintillator and 3Heproportional counters was constructed for the measurement of neutrons in the energy range 1–200MeV. We discuss its ...design, principles of operation, and the method of analysis. The detector is capable of observing very low neutron fluxes in the presence of ambient gamma background and does not require scintillator pulse-shape discrimination. The spectrometer was characterized for its energy response in fast neutron fields of 2.5MeV and 14MeV, and the results are compared with Monte Carlo simulations. Measurements of the fast neutron flux and energy response at 120m above sea-level (39.130°N, 77.218°W) and at a depth of 560m in a limestone mine are presented. Finally, the design of a spectrometer with improved sensitivity and energy resolution is discussed.
The violation of mirror symmetry in the weak force provides a powerful tool to study the internal structure of the proton. Experimental results have been obtained that address the role of strange ...quarks in generating nuclear magnetism. The measurement reported here provides an unambiguous constraint on strange quark contributions to the proton's magnetic moment through the electron-proton weak interaction. We also report evidence for the existence of a parity-violating electromagnetic effect known as the anapole moment of the proton. The proton's anapole moment is not yet well understood theoretically, but it could have important implications for precision weak interaction studies in atomic systems such as cesium.
One of the key elements to understanding the structure of the nucleon is the role of its quark–antiquark sea in its ground state properties such as charge, mass, magnetism and spin. In the last ...decade, parity-violating electron scattering has emerged as an important tool in this area, because of its ability to isolate the contribution of strange quark–antiquark pairs to the nucleon’s charge and magnetism. The
sample experiment at the MIT-Bates Laboratory, which has been focused on
s
¯
s
contributions to the proton’s magnetic moment, was the first of such experiments and its program has recently been completed. In this paper we give an overview of some of the experimental aspects of parity-violating electron scattering, briefly review the theoretical predictions for strange quark form factors, summarize the
sample measurements, and place them in context with the program of experiments being carried out at other electron scattering facilities such as Jefferson Laboratory and the Mainz Microtron.
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave ...function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep → e'pω , at central Q2 values of 1.60, 2.45 GeV2 , at W=2.21 GeV . The results of our pioneering -u≈-umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L / T / LT / TT separations in this never explored kinematic territory. At Q2=2.45 GeV2 , the observed dominance of σT over σL , is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.
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