Open Access

Christopher Lehr, Felix Wamers, Farouk Aksouh, Yuliya Aksyutina, Héctor Álvarez-Pol, Leyla Atar, Thomas Aumann, Saul Beceiro-Novo, Carlos A. Bertulani, Konstanze Boretzky, Maria José Garcia Borge, Christoph Caesar, Marielle Chartier, Audrey Chatillon, Leonid V. Chulkov, Dolores Cortina Gil, Paloma Díaz Fernández, Hans Emling, Olga Ershova, Luis M. Fraile Prieto, Hans Otto Uldall Fynbo, Daniel Galaviz Redondo, Hans Geissel, Michael Heil, Marcel Heine, Dieter H. H. Hoffmann, Matthias Holl, Håkan T. Johansson, Björn Jonson, Christos Karagiannis, Oleg A. Kiselev, Jens-Volker Kratz, Reinhard Kulessa, Nikolaus Kurz, Christoph Langer, Mattias Lantz, Tudi Le Bleis, Roy Crawford Lemmon, Yuri A. Litvinov, Bastian Löher, Kripamay Mahata, Justyna Marganiec-Galązka, Christian Müntz, Thomas Nilsson, Chiara Nociforo, Wolfgang Ott, Valerii Panin, Stefanos Paschalis, Angel Perea Martinez, Ralf Plag, René Reifarth, Achim Richter, Karsten Riisager, Carme Rodriguez-Tajes, Dominic M. Rossi, Deniz Savran, Heiko Scheit, Gerhard Schrieder, Philipp Schrock, Haik Simon, Joachim Stroth, Klaus Sümmerer, Olof Tengblad, Helmut Weick, Christine Wimmer

• The proton drip-line nucleus 17Ne is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the 17Ne(p, 2p)16F∗ →15O+p quasi-free one-proton knockout reaction has been performed at GSI at around 500 MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of 16F into 15O (including γ decays from excited states) and a proton, as well as the 15O+p relative-energy spectrum and the 16F momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l = 0 and l = 2 motion of the valence protons in 17Ne. With a resulting relatively small l = 0 component of only around 35(3)%, it is concluded that 17Ne exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the 15O core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections.