We report the first measurement of the (e,e′p) reaction cross-section ratios for Helium-3 (He3), Tritium (H3), and Deuterium (d). The measurement covered a missing momentum range of ...40≤pmiss≤550MeV/c, at large momentum transfer (〈Q2〉≈1.9 (GeV/c)2) and xB>1, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for He3/d and H3/d extend to just above the typical nucleon Fermi-momentum (kF≈250 MeV/c) and differ from each other by ∼20%, while for He3/H3 they agree within the measurement accuracy of about 3%. At momenta above kF, the measured He3/H3 ratios differ from the calculation by 20%−50%. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the He3/H3 cross-section ratio for this measurement by less than 5%. If these calculations are correct, then the differences at large missing momenta between the He3/H3 experimental and calculated ratios could be due to the underlying NN interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the NN interaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report the first longitudinal-transverse separation of the deeply virtual exclusive π^{0} electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure ...functions dσ_{L}/dt, dσ_{T}/dt, dσ_{LT}/dt, and dσ_{TT}/dt are extracted as a function of the momentum transfer to the recoil system at Q^{2}=1.75 GeV^{2} and x_{B}=0.36. The ed→edπ^{0} cross sections are found compatible with the small values expected from theoretical models. The en→enπ^{0} cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity generalized parton distributions of the nucleon. By combining these results with previous measurements of π^{0} electroproduction off the proton, we present a flavor decomposition of the u and d quark contributions to the cross section.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We present deeply virtual π0 electroproduction cross-section measurements at xB=0.36 and three different Q2 values ranging from 1.5 to 2 GeV2, obtained from Jefferson Lab Hall A experiment E07-007. ...The Rosenbluth technique is used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component and, thus, is far from the asymptotic limit predicted by perturbative quantum chromodynamics. Nonetheless, an indication of a nonzero longitudinal contribution is provided by the measured interference term σLT. Results are compared with several models based on the leading-twist approach of generalized parton distributions (GPDs). In particular, a fair agreement is obtained with models in which the scattering amplitude includes convolution terms of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. This experiment, together with previous extensive unseparated measurements, provides strong support to the exciting idea that transversity GPDs can be accessed via neutral pion electroproduction in the high-Q2 regime.
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We report a precision measurement of the parity-violating asymmetry A_{PV} in the elastic scattering of longitudinally polarized electrons from ^{208}Pb. We measure A_{PV}=550±16(stat)±8(syst) parts ...per billion, leading to an extraction of the neutral weak form factor F_{W}(Q^{2}=0.00616 GeV^{2})=0.368±0.013. Combined with our previous measurement, the extracted neutron skin thickness is R_{n}-R_{p}=0.283±0.071 fm. The result also yields the first significant direct measurement of the interior weak density of ^{208}Pb: ρ_{W}^{0}=-0.0796±0.0036(exp)±0.0013(theo) fm^{-3} leading to the interior baryon density ρ_{b}^{0}=0.1480±0.0036(exp)±0.0013(theo) fm^{-3}. The measurement accurately constrains the density dependence of the symmetry energy of nuclear matter near saturation density, with implications for the size and composition of neutron stars.
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Phys. Rev. Lett. 118, 222002 (2017) We report the first longitudinal/transverse separation of the deeply virtual
exclusive $\pi^0$ electroproduction cross section off the neutron and coherent
...deuteron. The corresponding four structure functions $d\sigma_L/dt$,
$d\sigma_T/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{TT}/dt$ are extracted as a
function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$
and $x_B$=0.36. The $ed \to ed\pi^0$ cross sections are found compatible with
the small values expected from theoretical models. The $en \to en\pi^0$ cross
sections show a dominance from the response to transversely polarized photons,
and are in good agreement with calculations based on the transversity GPDs of
the nucleon. By combining these results with previous measurements of $\pi^0$
electroproduction off the proton, we present a flavor decomposition of the $u$
and $d$ quark contributions to the cross section.
Phys. Rev. Lett. 117, 262001 (2016) We present deeply virtual $\pi^0$ electroproduction cross-section
measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5
to 2 GeV$^2$, ...obtained from experiment E07-007 that ran in the Hall A at
Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal
and transverse responses. Results demonstrate that the cross section is
dominated by its transverse component, and thus is far from the asymptotic
limit predicted by perturbative Quantum Chromodynamics. An indication of a
non-zero longitudinal contribution is provided by the interference term
$\sigma_{LT}$ also measured. Results are compared with several models based on
the leading twist approach of Generalized Parton Distributions (GPDs). In
particular, a fair agreement is obtained with models where the scattering
amplitude is described by a convolution of chiral-odd (transversity) GPDs of
the nucleon with the twist-3 pion distribution amplitude. Therefore, neutral
pion electroproduction may offer the exciting possibility of accessing
transversity GPDs through experiment.
We report on new p$(e,e^\prime p)\pi^\circ$ measurements at the
$\Delta^{+}(1232)$ resonance at the low momentum transfer region. The mesonic
cloud dynamics is predicted to be dominant and rapidly ...changing in this
kinematic region offering a test bed for chiral effective field theory
calculations. The new data explore the low $Q^2$ dependence of the resonant
quadrupole amplitudes while extending the measurements of the Coulomb
quadrupole amplitude to the lowest momentum transfer ever reached. The results
disagree with predictions of constituent quark models and are in reasonable
agreement with dynamical calculations that include pion cloud effects, chiral
effective field theory and lattice calculations. The reported measurements
suggest that improvement is required to the theoretical calculations and
provide valuable input that will allow their refinements.
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