Inclusive electron scattering at carefully chosen kinematics can isolate scattering from short-range correlations (SRCs), produced through hard, short-distance interactions of nucleons in the ...nucleus. Because the two-nucleon (2N) SRCs arise from the same N-N interaction in all nuclei, the cross section in the SRC-dominated regime is identical up to an overall scaling factor, and the A/2H cross section ratio is constant in this region. This scaling behavior has been used to identify SRC dominance and to map out the contribution of SRCs for a wide range of nuclei. We examine this scaling behavior at lower momentum transfers using new data on \(^2\)H, \(^3\)H, and \(^3\)He which show that the scaling region is larger than in heavy nuclei. Based on the improved scaling, especially for \(^3\)H/\(^3\)He, we examine the ratios at kinematics where three-nucleon SRCs may play an important role. The data for the largest initial nucleon momenta are consistent with isolation of scattering from 3N-SRCs, and suggest that the very-highest momentum nucleons in \(^3\)He have a nearly isospin-independent momentum configuration, or a small enhancement of the proton distribution.
We report the first measurement of the \eep three-body breakup reaction cross sections in helium-3 (\(^3\)He) and tritium (\(^3\)H) at large momentum transfer (\(\langle Q^2 \rangle \approx 1.9\) ...(GeV/c)\(^2\)) and \(x_B>1\) kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta \(40 \le p_{miss} \le 500\) MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab-initio calculations. Overall good agreement, within \(\pm20\%\), is observed between data and calculations for the full \(p_{miss}\) range for \(^3\)H and for \(100 \le p_{miss} \le 350\) MeV/c for \(^3\)He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at \(p_{miss} > 250\) MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of \(^3\)He plus \(^3\)H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire \(p_{miss}\) range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of \(500\) MeV/c.
The E12-14-012 experiment performed at Jefferson Lab Hall A has collected inclusive electron-scattering data for different targets at the kinematics corresponding to beam energy 2.222 GeV and ...scattering angle 15.54 deg. Here we present a comprehensive analysis of the collected data and compare the double-differential cross sections for inclusive scattering of electrons, extracted using solid targets (aluminum, carbon, and titanium) and a closed argon-gas cell. The data extend over broad range of energy transfer, where quasielastic interaction, Delta-resonance excitation, and inelastic scattering yield contributions to the cross section. The double-differential cross sections are reported with high precision (~3%) for all targets over the covered kinematic range.
Quasi-elastic scattering on \(^{12}\)C\((e,e'p)\) was measured in Hall C at Jefferson Lab for space-like 4-momentum transfer squared \(Q^2\) in the range of 8--14.2\,(GeV/\(c\))\(^2\) with proton ...momenta up to 8.3\,GeV/\(c\). The experiment was carried out in the upgraded Hall C at Jefferson Lab. It used the existing high momentum spectrometer and the new super high momentum spectrometer to detect the scattered electrons and protons in coincidence. The nuclear transparency was extracted as the ratio of the measured yield to the yield calculated in the plane wave impulse approximation. Additionally, the transparency of the \(1s_{1/2}\) and \(1p_{3/2}\) shell protons in \(^{12}\)C was extracted, and the asymmetry of the missing momentum distribution was examined for hints of the quantum chromodynamics prediction of Color Transparency. All of these results were found to be consistent with traditional nuclear physics and inconsistent with the onset of Color Transparency.
The success of the ambitious programs of both long- and short-baseline neutrino-oscillation experiments employing liquid-argon time-projection chambers will greatly rely on the precision with which ...the weak response of the argon nucleus can be estimated. In the E12-14-012 experiment at Jefferson Lab Hall A, we have studied the properties of the argon nucleus by scattering a high-quality electron beam off a high-pressure gaseous argon target. Here, we present the measured \(^{40}\)Ar\((e,e^{\prime})\) double differential cross section at incident electron energy \(E=2.222\)~GeV and scattering angle \(\theta = 15.541^\circ\). The data cover a broad range of energy transfers, where quasielastic scattering and delta production are the dominant reaction mechanisms. The result for argon is compared to our previously reported cross sections for titanium and carbon, obtained in the same kinematical setup.
Physics Letters B 797 (2019) 134890 We report the first measurement of the $(e,e'p)$ reaction cross-section
ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The
measurement covered ...a missing momentum range of $40 \le p_{miss} \le 550$
MeV$/c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$
(GeV$/c$)$^2$) and $x_B>1$, 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 $^3$He$/d$ and $^3$H$/d$ extend to just above the typical nucleon
Fermi-momentum ($k_F \approx 250$ MeV$/c$) and differ from each other by $\sim
20\%$, while for $^3$He/$^3$H they agree within the measurement accuracy of
about 3\%. At momenta above $k_F$, the measured $^3$He/$^3$H ratios differ from
the calculation by $20\% - 50\%$. Final state interaction (FSI) calculations
using the generalized Eikonal Approximation indicate that FSI should change the
$^3$He/$^3$H cross-section ratio for this measurement by less than 5\%. If
these calculations are correct, then the differences at large missing momenta
between the $^3$He/$^3$H 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.
Accurately measuring the neutron beam polarization of a high flux, large area neutron beam is necessary for many neutron physics experiments. The Fundamental Neutron Physics Beamline (FnPB) at the ...Spallation Neutron Source (SNS) is a pulsed neutron beam that was polarized with a supermirror polarizer for the NPDGamma experiment. The polarized neutron beam had a flux of \(\sim10^9\) neutrons per second per cm\(^2\) and a cross sectional area of 10\(\times\)12~cm\(^2\). The polarization of this neutron beam and the efficiency of a RF neutron spin rotator installed downstream on this beam were measured by neutron transmission through a polarized \(^{3}\)He neutron spin-filter. The pulsed nature of the SNS enabled us to employ an absolute measurement technique for both quantities which does not depend on accurate knowledge of the phase space of the neutron beam or the \(^{3}\)He polarization in the spin filter and is therefore of interest for any experiments on slow neutron beams from pulsed neutron sources which require knowledge of the absolute value of the neutron polarization. The polarization and spin-reversal efficiency measured in this work were done for the NPDGamma experiment, which measures the parity violating \(\gamma\)-ray angular distribution asymmetry with respect to the neutron spin direction in the capture of polarized neutrons on protons. The experimental technique, results, systematic effects, and applications to neutron capture targets are discussed.
Phys. Rev. Lett. 121, 242002 (2018) We report the first observation of the parity-violating 2.2 MeV gamma-ray
asymmetry $A^{np}_\gamma$ in neutron-proton capture using polarized cold
neutrons ...incident on a liquid parahydrogen target at the Spallation Neutron
Source at Oak Ridge National Laboratory. $A^{np}_\gamma$ isolates the $\Delta
I=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak
nucleon-nucleon interaction, which is dominated by pion exchange and can be
directly related to a single coupling constant in either the DDH meson exchange
model or pionless EFT. We measured $A^{np}_\gamma = -3.0 \pm 1.4 (stat) \pm
0.2 (sys)\times 10^{-8}$, which implies a DDH weak $\pi NN$ coupling of
$h_{\pi}^{1} = 2.6 \pm 1.2(stat) \pm 0.2(sys) \times 10^{-7}$ and a pionless
EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=-7.4 \pm 3.5 (stat)
\pm 0.5 (sys) \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data
analysis, systematic uncertainties, and the implications of the result.
To probe CP violation in the leptonic sector using GeV energy neutrino beams in current and future experiments using argon detectors, precise models of the complex underlying neutrino and ...antineutrino interactions are needed. The E12-14-012 experiment at Jefferson Lab Hall A was designed to perform a combined analysis of inclusive and exclusive electron scatterings on both argon (\(N = 22\)) and titanium (\(Z = 22\)) nuclei using GeV energy electron beams. The measurement on titanium nucleus provides essential information to understand the neutrino scattering on argon, large contribution to which comes from scattering off neutrons. Here we report the first experimental study of electron-titanium scattering as double differential cross section at beam energy \(E=2.222\) GeV and electron scattering angle \(\theta = 15.541\) deg, measured over a broad range of energy transfer, spanning the kinematical regions in which quasielastic scattering and delta production are the dominant reaction mechanisms. The data provide valuable new information needed to develop accurate theoretical models of the electromagnetic and weak cross sections of these complex nuclei in the kinematic regime of interest to neutrino experiments.
When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough together to feel significant attraction, or repulsion, from the strong, short-distance part of the ...nucleon-nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly-energetic nucleons referred to as short-range correlations (SRCs). SRCs are an important but relatively poorly understood part of nuclear structure and mapping out the strength and isospin structure (neutron-proton vs proton-proton pairs) of these virtual excitations is thus critical input for modeling a range of nuclear, particle, and astrophysics measurements. Hitherto measurements used two-nucleon knockout or ``triple-coincidence'' reactions to measure the relative contribution of np- and pp-SRCs by knocking out a proton from the SRC and detecting its partner nucleon (proton or neutron). These measurementsshow that SRCs are almost exclusively np pairs, but had limited statistics and required large model-dependent final-state interaction (FSI) corrections. We report on the first measurement using inclusive scattering from the mirror nuclei \(^3\)H and \(^3\)He to extract the np/pp ratio of SRCs in the A=3 system. We obtain a measure of the np/pp SRC ratio that is an order of magnitude more precise than previous experiments, and find a dramatic deviation from the near-total np dominance observed in heavy nuclei. This result implies an unexpected structure in the high-momentum wavefunction for \(^3\)He and \(^3\)H. Understanding these results will improve our understanding of the short-range part of the N-N interaction.
