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Pion photoproduction in the $\vec{\gamma }\vec{p}\to {\pi }^{0}p$ reaction has been measured in the FROzen Spin Target (FROST) experiment at the Thomas Jefferson National Accelerator Facility. In this experiment, circularly polarized photons with energies up to 3.082 GeV impinged on a transversely polarized frozen-spin target. Final-state protons were detected in the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer. The polarization observables $T$ and $F$ have been extracted for $W$ from 1445 to 2525 MeV, of which the energy range is much broader, and the precision is better than the existing measurements in higher $W$ ranges. The data generally agree with predictions of present partial-wave analyses but also show marked differences for higher $W$ ranges. By incorporating the present data into the databases, the Scattering Analysis Interactive Data (SAID) fits have been improved with relatively small ${\chi }^2$ and significant changes in the parameters of the $\mathrm{\Delta }\left(1910\right)1/2^{+}$ and $N\left(2190\right)7/2^{-}$ have been found with the JüBo model. 

The polarization of $\mathrm{\Lambda }$ hyperons is preserved in the angular distribution of their decay products. This property allows one to study the spin structure of the $\mathrm{\Lambda }$ . In semi-inclusive deep inelastic scattering where a high energy lepton interacts with a nucleon target and one or more hadrons and the scattered lepton are detected in the final state, the probability for a struck quark to impart the polarization of the lepton to the $\mathrm{\Lambda }$ may be measured. In particular, in electron-proton scattering this quantity may be related to the longitudinal light quark polarization of the $\mathrm{\Lambda }$ . Currently, limited experimental data cannot discriminate between different models of $\mathrm{\Lambda }$ spin structure. This work reports on the measurement of the longitudinal spin transfer $D_{L{L}^{\prime }}^{\mathrm{\Lambda }}$ to the $\mathrm{\Lambda }$ using data taken by the CLAS12 spectrometer at Jefferson Lab with a 10.6 GeV longitudinally polarized electron beam and an unpolarized hydrogen target. This measurement is the most precise to date, and, in comparison with theory predictions, it offers valuable insight into the relative dominance of current and target fragmentation in $\mathrm{\Lambda }$ production. 

Abstract We propose a new measurement of the ratio of positron-proton to electron-proton elastic scattering at DESY. The purpose is to determine the contributions beyond single-photon exchange, which are essential for the Quantum Electrodynamic (QED) description of the most fundamental process in hadronic physics. By utilizing a 20 cm long liquid hydrogen target in conjunction with the extracted beam from the DESY synchrotron, we can achieve an average luminosity of$$2.12\times 10^{35}$$ $2.12\times {10}^{35}$  cm$$^{-2}\cdot $$ ${}^{-2}·$ s$$^{-1}$$ ${}^{-1}$  ($$\approx 200$$ $\approx 200$ times the luminosity achieved by OLYMPUS). The proposed two-photon exchange experiment (TPEX) entails a commissioning run at a beam energy of 2 GeV, followed by measurements at 3 GeV, thereby providing new data up to$$Q^2=4.6$$ $Q^2=4.6$  (GeV/c)$$^2$$ ${}^2$ (twice the range of current measurements). We present and discuss the proposed experimental setup, run plan, and expectations. 

Measurements of beam single-spin asymmetries in semi-inclusive deep-inelastic electron scattering (SIDIS) with positively charged kaons off protons have been performed with 10.6 and 10.2 GeV incident electron beams using the CLAS12 spectrometer at Jefferson Lab. We report an analysis of the electroproduction of positively charged kaons over a large kinematic range of fractional energy, Bjorken $x$ , transverse momentum, and photon virtualities $Q^2$ ranging from 1 ${\mathrm{GeV}}^2$ up to 6 ${\mathrm{GeV}}^2$ . This is the first published multidimensionally binned CLAS12 measurement of a kaon SIDIS single-spin asymmetry in the valence quark regime. The data provide constraints on the structure function ratio $F_{LU}^{sin\varphi }/F_{UU}$ , where $F_{LU}^{sin\varphi }$ is a quantity with a leading twist of twist-3 that can reveal novel aspects of the quark-gluon correlations within the nucleon. The impact of the data on understanding the underlying reaction mechanisms and their kinematic variation is explored using theoretical models for the different contributing twist-3 parton-distribution functions (PDFs) and fragmentation functions (FFs). 

We present the first threefold differential measurement for neutral-pion multiplicity ratios produced in semi-inclusive deep-inelastic electron scattering on carbon, iron, and lead nuclei normalized to deuterium from CLAS at Jefferson Lab. We found that the neutral-pion multiplicity ratio is maximally suppressed for the leading hadrons (energy fraction $z\to$ 1), suppression varying from 25% in carbon up to 75% in lead. An enhancement of the multiplicity ratio at low $z$ and high $p_T^2$ is observed, suggesting an interconnection between these two variables. This behavior is qualitatively similar to the previous twofold differential measurement of charged pions by the HERMES Collaboration and, recently, by CLAS Collaboration. The largest enhancement was observed at high $p_T^2$ for heavier nuclei, namely, iron and lead, while the smallest enhancement was observed for the lightest nucleus, carbon. This behavior suggests a competition between partonic multiple scattering, which causes enhancement, and hadronic inelastic scattering, which causes suppression.