High-resolution hypernuclear spectroscopy at Jefferson Lab, Hall A

International audienceThe experiment E94-107 in Hall A at Jefferson Lab started a systematic study of high-resolution hypernuclear spectroscopy in the 0p-shell region of nuclei such as the hypernuclei produced in electroproduction on Be9,C12, and O16 targets. In order to increase counting rates and provide unambiguous kaon identification, two superconducting septum magnets and a ring-imaging Cherenkov detector were added to the Hall A standard equipment. The high-quality beam, the good spectrometers, and the new experimental devices allowed us to obtain very good results. For the first time, measurable strength with sub-MeV energy resolution was observed for the core-excited states of BΛ12. A high-quality NΛ16 hypernuclear spectrum was likewise obtained. A first measurement of the Λ binding energy for NΛ16, calibrated against the elementary reaction on hydrogen, was obtained with high precision, 13.76±0.16 MeV. Similarly, the first LiΛ9 hypernuclear spectrum shows general agreement with theory (distorted-wave impulse approximation with the SLA and BS3 electroproduction models and shell-model wave functions). Some disagreement exists with respect to the relative strength of the states making up the first multiplet. A Λ separation energy of 8.36 MeV was obtained, in agreement with previous results. It has been shown that the electroproduction of hypernuclei can provide information complementary to that obtained with hadronic probes and the γ-ray spectroscopy technique

Measurement of the 3He spin-structure functions and of neutron (3He) spin-dependent sum rules at 0.035 ≤ Q2 ≤ 0.24 GeV2

International audienceThe spin-structure functions g1 and g2, and the spin-dependent partial cross-section σTT have been extracted from the polarized cross-sections differences, Δσ∥(ν,Q2) and Δσ⊥(ν,Q2) measured for the He3→(e→,e′)X reaction, in the E97-110 experiment at Jefferson Lab. Polarized electrons with energies from 1.147 to 4.404 GeV were scattered at angles of 6∘ and 9∘ from a longitudinally or transversely polarized 3He target. The data cover the kinematic regions of the quasi-elastic, resonance production and beyond. From the extracted spin-structure functions, the first moments Γ1‾(Q2), Γ2(Q2) and ITT(Q2) are evaluated with high precision for the neutron in the Q2 range from 0.035 to 0.24GeV2. The comparison of the data and the chiral effective field theory predictions reveals the importance of proper treatment of the Δ degree of freedom for spin observables