Open Access

Valerii Panin, Jonathan Thomas Taylor, Stefanos Paschalis, Felix Wamers, Yuliya Aksyutina, Héctor Alvarez-Pol, Thomas Aumann, Carlos A. Bertulani, Konstanze Boretzky, Christoph Caesar, Marielle Chartier, L. V. Čulkov, Dolores Cortina Gil, Joachim Enders, Olga Ershova, Hans Geissel, Roman Gernhäuser, Michael Heil, Håkan T. Johansson, Björn Jonson, Aleksandra Kelić-Heil, Christoph Langer, Tudi Le Bleis, Roy Crawford Lemmon, Thomas Nilsson, Marina Petri, Ralf Plag, René Reifarth, Dominic M. Rossi, Heiko Scheit, Haik Simon, Helmut Weick, Christine Wimmer

• Quasi-free scattering reactions of the type (p, 2p)were measured for the first time exclusively in com-plete and inverse kinematics, using a 12C beam at an energy of ∼400MeV/u as a benchmark. This new technique has been developed to study the single-particle structure of exotic nuclei in experiments with radioactive-ion beams. The outgoing pair of protons and the fragments were measured simultaneously, enabling an unambiguous identification of the reaction channels and a redundant measurement of the kinematic observables. Both valence and deeply-bound nucleon orbits are probed, including those leading to unbound states of the daughter nucleus. Exclusive (p, 2p)cross sections of 15.8(18)mb, 1.9(2)mb and 1.5(2)mb to the low-lying 0p-hole states overlapping with the ground state (3/2−) and with the bound excited states of 11B at 2.125MeV (1/2−) and 5.02MeV (3/2−), respectively, were determined via γ-ray spectroscopy. Particle-unstable deep-hole states, corresponding to proton removal from the 0s-orbital, were studied via the invariant-mass technique. Cross sections and momentum distributions were ex-tracted and compared to theoretical calculations employing the eikonal formalism. The obtained results are in a good agreement with this theory and with direct-kinematics experiments. The dependence of the proton–proton scattering kinematics on the internal momentum of the struck proton and on its sep-aration energy was investigated for the first time in inverse kinematics employing a large-acceptance measurement.