In 2018, the E12-17-003 experiment was conducted at the Thomas Jefferson National Accelerator Facility (JLab) to explore the possible existence of an nnLambda state in the reconstructed missing mass ...distribution from a tritium gas target K. N. Suzuki et al., Prog. Theor. Exp. Phys. 2022, 013D01 (2022), B. Pandey et al., Phys. Rev. C 105, L051001 (2022). As part of this investigation, data was also collected using a gaseous hydrogen target, not only for a precise absolute mass scale calibration but also for the study of Lambda/Sigma^0 electroproduction. This dataset was acquired at Q^2~0.5 (GeV/c)^2, W=2.14 GeV, and theta_{gamma K}^{c.m.}~8 deg. It covers forward angles where photoproduction data is scarce and a low-Q^2 region that is of interest for hypernuclear experiments. On the other hand, this kinematic region is at a slightly higher Q^2 than previous hypernuclear experiments, thus providing crucial information for understanding the Q^2 dependence of the differential cross sections for Lambda/Sigma^0 hyperon electroproduction. This paper reports on the Q^2 dependence of the differential cross section for the e + p -> e' + K^+ + Lambda/Sigma^0 reaction in the 0.2-0.8 (GeV/c)^2, and provides comparisons with the currently available theoretical models.
The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively ...straightforward, the lack of a free neutron target makes measurements of the neutron's electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei \(^3\)H and \(^3\)He, where the nuclear effects are larger than for deuterium but expected to largely cancel in the cross-section ratios. We extracted values of the neutron magnetic form factor for low-to-modest momentum transfer, \(0.6<Q^2<2.9\) GeV\(^2\), where existing measurements give inconsistent results. The precision and \(Q^2\) range of this data allow for a better understanding of the current world's data, and suggest a path toward further improvement of our overall understanding of the neutron's magnetic form factor.
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 on the results of the first search for the production of axion-like particles (ALP) via Primakoff production on nuclear targets using the GlueX detector. This search uses an integrated ...luminosity of 100 pb\(^{-1}\cdot\)nucleon on a \(^{12}\)C target, and explores the mass region of 200 < \(m_a\) < 450 MeV via the decay \(X\rightarrow\gamma\gamma\). This mass range is between the \(\pi^0\) and \(\eta\) masses, which enables the use of the measured \(\eta\) production rate to obtain absolute bounds on the ALP production with reduced sensitivity to experimental luminosity and detection efficiency. We find no evidence for an ALP, consistent with previous searches in the quoted mass range, and present limits on the coupling on the scale of \(O\)(1 TeV). We further find that the ALP production limit we obtain is hindered by the peaking structure of the non-target-related dominant background in GlueX, which we treat by using data on \(^4\)He to estimate and subtract these backgrounds. We comment on how this search can be improved in a future higher-statistics dedicated measurement.
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 proton is one of the main building blocks of all visible matter in the universe. Among its intrinsic properties are its electric charge, mass, and spin. These emerge from the complex dynamics of ...its fundamental constituents, quarks and gluons, described by the theory of quantum chromodynamics (QCD). Using electron scattering, its electric charge and spin, shared among the quark constituents, have been the topic of active investigation. An example is the novel precision measurement of the proton's electric charge radius. In contrast, little is known about the proton's inner mass density, dominated by the energy carried by the gluons, which are hard to access through electron scattering since gluons carry no electromagnetic charge. Here, we chose to probe this gluonic gravitational density using a small color dipole, the \(J/\psi\) particle, through its threshold photoproduction. From our data, we determined, for the first time, the proton's gluonic gravitational form factors. We used a variety of models and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some cases, the determined radius, although model dependent, is in excellent agreement with first-principle predictions from lattice QCD. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.
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