Exclusive measurements of quasi-free proton scattering reactions in inverse and complete kinematics

Quasi-free scattering reactions of the type (p, 2p) were measured for the first time exclusively in complete
\nand inverse kinematics, using a 12C beam at an energy of ∼400 MeV/u as a benchmark. This new
\ntechnique has been developed to study the single-particle structure of exotic nuclei in experiments with
\nradioactive-ion beams. The outgoing pair of protons and the fragments were measured simultaneously,
\nenabling an unambiguous identification of the reaction channels and a redundant measurement of the
\nkinematic observables. Both valence and deeply-bound nucleon orbits are probed, including those leading
\nto unbound states of the daughter nucleus. Exclusive (p, 2p) cross sections of 15.8(18) mb, 1.9(2) mb and
\n1.5(2) mb to the low-lying 0p-hole states overlapping with the ground state (3/2−) and with the bound
\nexcited states of 11B at 2.125 MeV (1/2−) and 5.02 MeV (3/2−), respectively, were determined via γ -ray
\nspectroscopy. Particle-unstable deep-hole states, corresponding to proton removal from the 0s-orbital,
\nwere studied via the invariant-mass technique. Cross sections and momentum distributions were extracted
\nand compared to theoretical calculations employing the eikonal formalism. The obtained results
\nare in a good agreement with this theory and with direct-kinematics experiments. The dependence of
\nthe proton–proton scattering kinematics on the internal momentum of the struck proton and on its separation
\nenergy was investigated for the first time in inverse kinematics employing a large-acceptance
\nmeasurement.