We present results on the electroexcitation of the low mass resonances (1232)P 33 , N (1440)P 11 , N (1520)D 13 , and N (1535)S 11 in a wide range of Q 2 . The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches-fixed-t dispersion relations and a unitary isobar model-allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the (1232)P 33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 6 GeV 2 . For the Roper resonance, N (1440)P 11 , the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S 11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison with the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D 13 and N (1535)S 11 longitudinal helicity amplitudes with good precision. For the N (1535)S 11 , these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N (1520)D 13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.

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Measurement of two-and three-nucleon shortrange correlation probabilities in nuclei KS The ratios of inclusive electron scattering cross sections of 4 He, 12 C, and 56 Fe to 3 He have been measured at 1 < x B < 3. At Q 2 > 1:4 GeV 2 , the ratios exhibit two separate plateaus, at 1:5 < x B < 2 and at x B > 2:25. This pattern is predicted by models that include 2-and 3-nucleon short-range correlations (SRC). Relative to A 3, the per-nucleon probabilities of 3-nucleon SRC are 2.3, 3.1, and 4.4 times larger for A 4, 12, and 56. This is the first measurement of 3-nucleon SRC probabilities in nuclei.

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The quantum numbers of the Xð3872Þ meson are determined to be J PC ¼ 1 þþ based on angular correlations in B þ ! Xð3872ÞK þ decays, where Xð3872Þ ! þ À J=c and J=c ! þ À . The data correspond to 1:0 fb À1 of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J PC ¼ 2 Àþ is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the Xð3872Þ state.