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.
The nuclear dependence of the inclusive inelastic electron scattering cross section (the EMC effect) has been measured for the first time in \(^{10}\)B and \(^{11}\)B. Previous measurements of the ...EMC effect in \(A \leq 12\) nuclei showed an unexpected nuclear dependence; \(^{10}\)B and \(^{11}\)B were measured to explore the EMC effect in this region in more detail. Results are presented for \(^9\)Be, \(^{10}\)B, \(^{11}\)B, and \(^{12}\)C at an incident beam energy of 10.6~GeV. The EMC effect in the boron isotopes was found to be similar to that for \(^9\)Be and \(^{12}\)C, yielding almost no nuclear dependence in the EMC effect in the range \(A=4-12\). This represents important, new data supporting the hypothesis that the EMC effect depends primarily on the local nuclear environment due to the cluster structure of these nuclei.
The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the (e,e'p) cross section in parallel kinematics using a natural titanium target. Here, we report the full results of the ...analysis of the data set corresponding to beam energy 2.2 GeV, and spanning the missing momentum and missing energy range 15 <= pm <= 250 MeV/c and 12 <= Em <= 80 MeV. The reduced cross section has been measured with ~7% accuracy as function of both missing momentum and missing energy. We compared our data to the results of a Monte Carlo simulations performed using a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations is quite good (chi2/d.o.f. = 0.9).
Nature 609, 41-45 (2022) 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.
We report a measurement of two energy-weighted gamma cascade angular distributions from polarized slow neutron capture on the \({}^{35}\)Cl nucleus, one parity-odd correlation proportional to ...\(\vec{s_{n}} \cdot \vec{k_{\gamma}}\) and one parity-even correlation proportional to \(\vec{s_{n}} \cdot \vec{k_{n}} \times \vec{k_{\gamma}}\). A parity violating asymmetry can appear in this reaction due to the weak nucleon-nucleon (NN) interaction which mixes opposite parity S and P-wave levels in the excited compound \(^{36}\)Cl nucleus formed upon slow neutron capture. If parity-violating (PV) and parity-conserving (PC) terms both exist, the measured differential cross section can be related to them via \(\frac{d\sigma}{d\Omega}\propto1+A_{\gamma, PV}\cos\theta+A_{\gamma,PC}\sin\theta\). The PV and PC asymmetries for energy-weighted gamma cascade angular distributions for polarized slow neutron capture on \(^{35}\)Cl averaged over the neutron energies from 2.27~meV to 9.53~meV were measured to be \(A_{\gamma,PV}=(-23.9\pm0.7)\times 10^{-6}\) and \(A_{\gamma,PC}=(0.1\pm0.7)\times 10^{-6}\). These results are consistent with previous experimental results. Systematic errors were quantified and shown to be small compared to the statistical error. These asymmetries in the angular distributions of the gamma rays emitted from the capture of polarized neutrons in \(^{35}\)Cl were used to verify the operation and data analysis procedures for the NPDGamma experiment which measured the parity-odd asymmetry in the angular distribution of gammas from polarized slow neutron capture on protons.
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 E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the \((e, e'p)\) cross section in parallel kinematics using a natural argon target. Here, we report the full results of the ...analysis of the data set corresponding to beam energy 2.222 GeV, and spanning the missing momentum and missing energy range \(15 \lesssim p_m \lesssim 300\) MeV/c and \(12 \lesssim E_m \lesssim 80\) MeV. The reduced cross section, determined as a function of \(p_m\) and \(E_m\) with \(\approx\)4\% accuracy, has been fitted using the results of Monte Carlo simulations involving a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations turns out to be quite satisfactory (\(\chi^2\)/n.d.o.f.=1.9). The resulting spectral function will provide valuable new information, needed for the interpretation of neutrino interactions in liquid argon detectors.
The ratio of the nucleon $F_2$ structure functions, $F_2^n/F_2^p$, is
determined by the MARATHON experiment from measurements of deep inelastic
scattering of electrons from $^3$H and $^3$He nuclei. ...The experiment was
performed in the Hall A Facility of Jefferson Lab and used two high resolution
spectrometers for electron detection, and a cryogenic target system which
included a low-activity tritium cell. The data analysis used a novel technique
exploiting the mirror symmetry of the two nuclei, which essentially eliminates
many theoretical uncertainties in the extraction of the ratio. The results,
which cover the Bjorken scaling variable range $0.19 < x < 0.83$, represent a
significant improvement compared to previous SLAC and Jefferson Lab
measurements for the ratio. They are compared to recent theoretical
calculations and empirical determinations of the $F_2^n/F_2^p$ ratio.
Phys. Rev. C 103, 034604 (2021) The E12-14-012 experiment, performed in Jefferson Lab Hall A, has collected
exclusive electron-scattering data (e,e$^\prime$p) in parallel kinematics using
natural ...argon and natural titanium targets. Here, we report the first results
of the analysis of the data set corresponding to beam energy of 2,222 MeV,
electron scattering angle 21.5 deg, and proton emission angle -50 deg. The
differential cross sections, measured with $\sim$4% uncertainty, have been
studied as a function of missing energy and missing momentum, and compared to
the results of Monte Carlo simulations, obtained from a model based on the
Distorted Wave Impulse Approximation.
Phys. Rev. Lett. 126, 082301 (2021) Quasielastic $^{12}$C$(e,e'p)$ scattering was measured at space-like
4-momentum transfer squared $Q^2$~=~8, 9.4, 11.4, and 14.2 (GeV/c)$^2$, the
highest ever ...achieved to date. Nuclear transparency for this reaction was
extracted by comparing the measured yield to that expected from a plane-wave
impulse approximation calculation without any final state interactions. The
measured transparency was consistent with no $Q^2$ dependence, up to proton
momenta of 8.5~GeV/c, ruling out the quantum chromodynamics effect of color
transparency at the measured $Q^2$ scales in exclusive $(e,e'p)$ reactions.
These results impose strict constraints on models of color transparency for
protons.
