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Register a new userInclusive Electron Scattering from Nuclei at $x simeq 1$
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The inclusive A(e,e) cross section for $x simeq 1$ was measured on $^2$H, C, Fe, and Au for momentum transfers $Q^2$ from 1-7 (GeV/c)$^2$. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit $xi$-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.
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Inclusive quasi-elastic electron scattering off nuclei is investigated at high momentum transfer (Q^2>1 (GeV/c)^2) and x>1 adopting a consistent treatment of nucleon-nucleon correlations in initial and final states. It is shown that in case of light as well as complex nuclei the inclusive cross section at 1.3<x<2 is dominated by the absorption of the virtual photon on a pair of correlated nucleons and by their elastic rescattering in the continuum, whereas at x>2 it is governed by the rescattering of the outgoing off-mass-shell nucleon in the complex optical potential generated by the ground state of the residual (A-1)-nucleon system.
The experiment, E08-014, in Hall-A at Jefferson Lab aims to study the short-range correlations (SRC) which are necessary to explain the nuclear strength absent in the mean field theory. The cross sections for $mathrm{^{2}H}$, $mathrm{^{3}He}$, $mathrm{^{4}He}$, $mathrm{^{12}C}$, $mathrm{^{40}Ca}$ and $mathrm{^{48}Ca}$, were measured via inclusive quasielastic electron scattering from these nuclei in a $mathrm{Q^{2}}$ range between 0.8 and $mathrm{2.8~(GeV/c)^{2}}$ for $x_{bj}>1$. The cross section ratios of heavy nuclei to $mathrm{^{2}H}$ were extracted to study two-nucleon SRC for $1<x_{bj}<2$, while the study of three-nucleon SRC was carried out from the cross section ratios of heavy nuclei to $mathrm{^{3}He}$ for $x_{bj}ge 2$. Meanwhile, the isospin dependence in SRCs has also been examined through the cross section ratio of $mathrm{^{48}Ca}$ and $mathrm{^{40}Ca}$.
We report on the highest precision yet achieved in the measurement of the polarization of a low energy, $mathcal{O}$(1 GeV), electron beam, accomplished using a new polarimeter based on electron-photon scattering, in Hall~C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond micro-strip detector which was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector and its large acceptance. The polarization of the $180~mu$A, $1.16$~GeV electron beam was measured with a statistical precision of $<$~1% per hour and a systematic uncertainty of 0.59%. This exceeds the level of precision required by the qweak experiment, a measurement of the vector weak charge of the proton. Proposed future low-energy experiments require polarization uncertainty $<$~0.4%, and this result represents an important demonstration of that possibility. This measurement is also the first use of diamond detectors for particle tracking in an experiment.
We present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic $^{14}$NH$_3$ target, and extracted double and single target spin asymmetries for $eprightarrow e^primepi^0X$ in multidimensional bins in four-momentum transfer ($1.0<Q^2<3.2$ GeV$^2$), Bjorken-$x$ ($0.12<x<0.48$), hadron energy fraction ($0.4<z<0.7$), transverse pion momentum ($0<P_T<1.0$ GeV), and azimuthal angle $phi_h$ between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both $x$ and $P_T$, which provide access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on $P_T$. The $sin 2phi_h$ moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed $sinphi_h$ moments suggest that quark gluon correlations are significant at large $x$.
A relativistic single particle model is used to calculate the inclusive $(e,e)$ reaction from $A=$12, 40, 56, 197, and 208 nuclei in the quasielastic region. We have shown that this model provides a very good description of the available experimental cross sections when they are dominated by the quasielastic process. In this paper we use this model to investigate the dependence of $y$-scaling on electron kinematics, particularly the electron scattering angle, for a range of squared four momentum transfer $0.20-0.80$ (GeV/c)$^2$. In this kinematic domain, Coulomb distortion of the electron does not significantly affect scaling, but final state interactions of the knocked out nucleon do affect scaling particularly when the nucleons have lower energies. In general, we find that scaling works for this reaction, but at lower values of the four momentum transfer, the scaling function does have some dependence on the electron scattering angle. We also consider a modification of y-scaling to include small binding energy effects as a function of Z and A and show that there is some improvement in scaling.
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