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Register a new userThe proton and deuteron F_2 structure function at low Q^2
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Measurements of the proton and deuteron $F_2$ structure functions are presented. The data, taken at Jefferson Lab Hall C, span the four-momentum transfer range $0.06 < Q^2 < 2.8$ GeV$^2$, and Bjorken $x$ values from 0.009 to 0.45, thus extending the knowledge of $F_2$ to low values of $Q^2$ at low $x$. Next-to-next-to-leading order calculations using recent parton distribution functions start to deviate from the data for $Q^2<2$ GeV$^2$ at the low and high $x$-values. Down to the lowest value of $Q^2$, the structure function is in good agreement with a parameterization of $F_2$ based on data that have been taken at much higher values of $Q^2$ or much lower values of $x$, and which is constrained by data at the photon point. The ratio of the deuteron and proton structure functions at low $x$ remains well described by a logarithmic dependence on $Q^2$ at low $Q^2$.
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The deuteron deep inelastic unpolarized structure function F_2^D is calculated using the Wilson operator product expansion method. The long distance behaviour, related to the deuteron bound state properties, is evaluated using the Bethe-Salpeter equation with one particle on mass shell. The calculation of the ratio F_2^D/F_2^N is compared with other convolution models showing important deviations in the region of large x. The implications in the evaluation of the neutron structure function from combined data on deuterons and protons are discussed.
We measured the $g_1$ spin structure function of the deuteron at low $Q^{2}$, where QCD can be approximated with chiral perturbation theory ($chi$PT). The data cover the resonance region, up to an invariant mass of $Wapprox1.9$~GeV. The generalized Gerasimov-Drell-Hearn sum, the moment $bar{Gamma}_{1}^{d}$ and the integral $bar{I}_gamma^d$ related to the spin polarizability $gamma_{0}^{d}$ are precisely determined down to a minimum $Q^2$ of 0.02~GeV$^2$ for the first time, about 2.5 times lower than that of previous data. We compare them to several $chi$PT calculations and models. These results are the first in a program of benchmark measurements of polarization observables in the $chi$PT domain.
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 present measurements of differential cross sections and the analyzing powers A_y, iT11, T20, T21, and T22 at E_c.m.=431.3 keV. In addition, an excitation function of iT11(theta_c.m.=87.8 degrees) for 431.3 <= E_c.m. <= 2000 keV is presented. These data are compared to calculations employing realistic nucleon-nucleon interactions, both with and without three-nucleon forces. Excellent agreement with the tensor analyzing powers and cross section is found, while the Ay and iT11 data are found to be underpredicted by the calculations.
Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. While differences are found, the parameterizations generally agree with the data even at the very low Q^2 scale of the data. The deuterium data show a smaller longitudinal structure function, and smaller ratio of longitudinal to transverse cross section R, than the proton. This suggests either an unexpected difference in R for the proton and neutron or a suppression of the gluonic distribution in nuclei.
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