Gabriel Niculescu

Observation of the Helium 7 {Lambda} hypernucleus by the (e,e'K+) reaction

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, (Λ)(7)He, was observed for the first time with the (e, eK+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The (Λ)(7)He binding energy supplies the last missing information of the A = 7, T = 1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.

HYPERNUCLEAR SPECTROSCOPY WITH ELECTRON BEAM AT JLab HALL C

Hypernuclear spectroscopy with electron beam at JLab Hall C has been studied since 2000. The first experiment, JLab E89-009, demonstrated the possibility of the (e, e′ K+) reaction for hypernuclear spectroscopy by achieving an energy resolution of better than 1 MeV (FWHM). The second experiment, JLab E01-011 employed a newly constructed high resolution kaon spectrometer and introduced a vertically tilted electron arm setup to avoid electrons from bremsstrahlung and Moeller scattering. The setup allowed us to have 10 times yield rate and 4 times better signal to accidental ratio with expected energy resolution of 400 keV (FWHM). The third experiment, JLab E05-115 will be performed in 2009 with employing newly constructed high resolution electron spectrometer and a new charge-separation magnet. With the fully customized third generation experimental setup, we can study a variety of targets up to medium-heavy ones such as 52Cr.

Quark-hadron duality in the free neutron F2 structure function

The Thomas Jefferson National Accelerator Facility (JLab) experiment BONuS used a novel spectator-tagging technique to measure the inclusive electron-free neutron scattering cross section and extract the F2 structure function. This data was used to reconstruct moments of F2 in the three prominent resonance region and the moments integrated over the entire resonance region. Comparisons of the experimental results with moments obtained from global parton distribution function parametrization seem to suggest that the quark-hadron duality hypothesis holds locally for the neutron in the second and third resonance regions down to Q2 of 1 GeV2; with up to 20% violations observed in the first resonance region.

Excited baryon form factors at high Q2

The role of resonance electroproduction at high Q2 is discussed in the context of exclusive reactions, as well as the alternative theoretical models which are proposed to treat exclusive reactions in the few GeV2/c2 region of momentum transfer. Jefferson Lab experiment 94-014, which measured the excitation of the Δ(1232) and S11(1535) via the reactions p(e,e′p)π0 and p(e,e′p)η respectively at Q2∼2.8 and 4u2009GeV2/c2 is described, and the state of analysis reported.

Associated Λ production at Jefferson lab

Abstract The 1 H(e, e′K + )Λ and 1 H(e,e′K + )Σ 0 reactions were studied as a function of the squared four-momentum-transfer, Q 2 , and the virtual photon polarization, e, thus enabling the separation of the longitudinal and transverse parts of the cross section. The existence of a sizable longitudinal component for the 1 H(e,e′K + )Λ reaction seems to be indicated by these data.

Excited baryon form factors at high Q{sup 2}

The role of resonance electroproduction at high Q2 is discussed in the context of exclusive reactions, as well as the alternative theoretical models which are proposed to treat exclusive reactions in the few GeV2/c2 region of momentum transfer. Jefferson Lab experiment 94-014, which measured the excitation of the Δ(1232) and S11(1535) via the reactions p(e,e′p)π0 and p(e,e′p)η respectively at Q2∼2.8 and 4u2009GeV2/c2 is described, and the state of analysis reported.

Excited baryon form factors at high

The role of resonance electroproduction at high Q2 is discussed in the context of exclusive reactions, as well as the alternative theoretical models which are proposed to treat exclusive reactions in the few GeV2/c2 region of momentum transfer. Jefferson Lab experiment 94-014, which measured the excitation of the Δ(1232) and S11(1535) via the reactions p(e,e′p)π0 and p(e,e′p)η respectively at Q2∼2.8 and 4u2009GeV2/c2 is described, and the state of analysis reported.