Understanding the strong interaction dynamics that govern the emergence of hadron mass (EHM) represents a challenging open problem in the Standard Model. In this paper we describe new opportunities for gaining insight into EHM from results on nucleon resonance ($N^{*}$) electroexcitation amplitudes (i.e., ${\gamma }_{v}p{N}^{*}$ electrocouplings) in the mass range up to 1.8 GeV for virtual photon four-momentum squared (i.e., photon virtualities $Q^2$) up to 7.5 GeV${}^2$ available from exclusive meson electroproduction data acquired during the 6-GeV era of experiments at Jefferson Laboratory (JLab). These results, combined with achievements in the use of continuum Schwinger function methods (CSMs), offer new opportunities for charting the momentum dependence of the dressed quark mass from results on the $Q^2$-evolution of the ${\gamma }_{v}p{N}^{*}$ electrocouplings. This mass function is one of the three pillars of EHM and its behavior expresses influences of the other two, viz. the running gluon mass and momentum-dependent effective charge. A successful description of the $\Delta \left(1232\right)3/2^{+}$ and $N\left(1440\right)1/2^{+}$ electrocouplings has been achieved using CSMs with, in both cases, common momentum-dependent mass functions for the dressed quarks, for the gluons, and the same momentum-dependent strong coupling. The properties of these functions have been inferred from nonperturbative studies of QCD and confirmed, e.g., in the description of nucleon and pion elastic electromagnetic form factors. Parameter-free CSM predictions for the electrocouplings of the $\Delta \left(1600\right)3/2^{+}$ became available in 2019. The experimental results obtained in the first half of 2022 have confirmed the CSM predictions. We also discuss prospects for these studies during the 12-GeV era at JLab using the CLAS12 detector, with experiments that are currently in progress, and canvass the physics motivation for continued studies in this area with a possible increase of the JLab electron beam energy up to 22 GeV. Such an upgrade would finally enable mapping of the dressed quark mass over the full range of distances (i.e., quark momenta) where the dominant part of hadron mass and $N^{*}$ structure emerge in the transition from the strongly coupled to perturbative QCD regimes.

Nuclear transparency, T-p(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extracted for quasi-elastic A(e, e' p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this Letter we extract a novel observable, the transparency ratio, T-p(A)/T-p(C-12), for knockout of high-missing-momentum protons from the breakup of short-range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q(2) >= 1.5 (GeV/c)(2) and x(B) >= 1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20-30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A(-1/3), which is consistent with dominance of scattering from nucleons at the nuclear surface. (C) 2013 Elsevier B.V. All rights reserved

Background: The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections.

The electroexcitation amplitudes or ${\gamma }_{v}p{N}^{*}$ electrocouplings of the $N\left(1440\right)1/2^{+}$, $N\left(1520\right)3/2^{-}$, and $\mathrm{\Delta }\left(1600\right)3/2^{+}$ resonances were obtained for the first time from the $ep\to e^{\prime }{\pi }^{+}{\pi }^{-}{p}^{\prime }$ differential cross sections measured with the CLAS detector at Jefferson Lab within the range of invariant mass $W=1.4\text{–}1.7$ GeV of the final state hadrons, for photon virtualities $Q^2=2.0\text{–}5.0$ ${\mathrm{GeV}}^2$. A good description of the nine independent onefold differential ${\gamma }_{v}p\to {\pi }^{+}{\pi }^{-}{p}^{\prime }$ cross sections achieved within the data-driven Jefferson Lab-Moscow State University (JM) meson-baryon reaction model in each bin of ($W,Q^2$) allows for separation of the resonant and nonresonant contributions. The electrocouplings were determined in the fits of the ${\pi }^{+}{\pi }^{-}p$ cross sections within three overlapping $W$ intervals with a substantial contribution from each of the three resonances listed above. Consistent results on the electrocouplings extracted from the data in these $W$ intervals provide evidence for their reliable extraction. These studies extend information on the electrocouplings of the $N\left(1440\right)1/2^{+}$ and $N\left(1520\right)3/2^{-}$ available from this channel over a broader range of $Q^2$. The electrocouplings of the $\mathrm{\Delta }\left(1600\right)3/2^{+}$, which decays preferentially into $\pi \pi N$ final states, have been determined for the first time. The reliable extraction of the electrocouplings for these states is also supported by the description of the ${\pi }^{+}{\pi }^{-}p$ differential cross sections with $Q^2$-independent masses and total/partial hadronic decay widths into the $\pi \mathrm{\Delta }$ and $\rho p$ final states.

We report on the first measurement of the differential cross section of phi-meson photoproduction for the d(gamma, pK(+)K(-))n exclusive reaction channel. The experiment was performed using a tagged-photon beam and the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. A combined analysis using data from the d(gamma, pK(+)K(-))n channel and those from a previous publication on coherent phi production on the deuteron has been carried out to extract the phi - N total cross section, sigma(phi N). The extracted phi - N total cross section favors a value above 20 mb. This value is larger than the value extracted using vector-meson dominance models for phi photoproduction on the proton