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Register a new userParity-Violating Inelastic Electron-Proton Scattering at Low $Q^2$ Above the Resonance Region
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We report the measurement of the parity-violating asymmetry for the inelastic scattering of electrons from the proton, at $Q^2 = 0.082$ GeV$^2$ and $ W = 2.23$ GeV, above the resonance region. The result $A_{rm Inel} = - 13.5 pm 2.0 ({rm stat}) pm 3.9 ({rm syst})$~ppm agrees with theoretical calculations, and helps to validate the modeling of the $gamma Z$ interference structure functions $F_1^{gamma Z}$ and $F_2^{gamma Z}$ used in those calculations, which are also used for determination of the two-boson exchange box diagram ($Box_{gamma Z}$) contribution to parity-violating elastic scattering measurements. A positive parity-violating asymmetry for inclusive $pi^-$ production was observed, as well as positive beam-normal single-spin asymmetry for scattered electrons and a negative beam-normal single-spin asymmetry for inclusive $pi^-$ production.
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The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. The parity-violating deep-inelastic asymmetries were used to extract the electron-quark weak effective couplings, and the resonance asymmetries provided the first evidence for quark-hadron duality in electroweak observables. These electron asymmetries and their interpretation were published earlier, but are presented here in more detail.
We analyze the parity-violating (PV) components of the analyzing power in elastic electron-proton scattering and discuss their sensitivity to the strange quark contributions to the proton weak form factors. We point out that the component of the analyzing power along the momentum transfer is independent of the electric weak form factor and thus compares favorably with the PV beam asymmetry for a determination of the strangeness magnetic moment. We also show that the transverse component could be used for constraining the strangeness radius. Finally, we argue that a measurement of both components could give experimental information on the strangeness axial charge.
Systematic differences in the the protons charge radius, as determined by ordinary atoms and muonic atoms, have caused a resurgence of interest in elastic lepton scattering measurements. The protons charge radius, defined as the slope of the charge form factor at Q$^2$=0, does not depend on the probe. Any difference in the apparent size of the proton, when determined from ordinary versus muonic hydrogen, could point to new physics or need for the higher order corrections. While recent measurements seem to now be in agreement, there is to date no high precision elastic scattering data with both electrons and positrons. A high precision proton radius measurement could be performed in Hall B at Jefferson Lab with a positron beam and the calorimeter based setup of the PRad experiment. This measurement could also be extended to deuterons where a similar discrepancy has been observed between the muonic and electronic determination of deuteron charge radius. A new, high precision measurement with positrons, when viewed alongside electron scattering measurements and the forthcoming MUSE muon scattering measurement, could help provide new insights into the origins of the proton radius puzzle, and also provide new experimental constraints on radiative correction calculations.
We report on parity-violating asymmetries in the nucleon resonance region measured using $5 - 6$ GeV longitudinally polarized electrons scattering off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the $Delta(1232)$, and provide a verification of quark-hadron duality in the nucleon electroweak $gamma Z$ interference structure functions at the (10-15)% level. The results are of particular interest to models relevant for calculating the $gamma Z$ box-diagram corrections to elastic parity-violating electron scattering measurements.
The $e^{+}p$ and $e^{-}p$ scattering data recorded at HERA during the recent years offer the possibility to study electroweak effects in $ep$ interactions apparent at high momentum transfers, $Q^{2}$, and to reveal information on the proton parton densities at large values of the Bjorken scaling variable x. From the neutral current cross section measurements, H1 and ZEUS extract the generalized structure function $x{cal F}_{3}$, which can be related to the valence quark content of the proton. Individual quark densities are extracted by a global fit to the H1 neutral and charged current $e^{+}p$ and $e^{-}p$ data. The new results show the sensitivity of high $Q^{2}$ $ep$ data to the structure of the proton and indicate what to expect from a 1 fb$^{-1}$ data sample to be taken by H1 and ZEUS until 2006 at the upgraded HERA collider. Future perspectives concerning the investigation of electroweak effects and their utilization to extract the parton content of the proton are shortly discussed.
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