Fig. 2: Experimental set-up and charged fragments momenta.
Left: schematic view of the experimental set-up. The 8He secondary beam at 156 MeV per nucleon is transported from the BigRIPS (Big RIKEN projectile-fragment separator) into the SAMURAI set-up, where it hits a liquid-hydrogen (LH2) target. In a quasi-elastic \(({\rm{p}},\,{{\rm{p}}}^{4}{\rm{He}})\) reaction, the 4He core is knocked out from the 8He projectile. Scintillator detectors and drift chambers are used for beam identification and tracking. The trajectories of the outgoing fragments are tracked by three silicon (Si) planes and bent afterwards through the SAMURAI spectrometer towards the focal-plane detectors. Two neutron-detector arrays were placed at a forward angle behind the SAMURAI. An additional scintillator wall was placed at smaller bending angle to detect the unreacted 8He beam. Right: measured momenta of the knocked-out 4He and the scattered proton after the quasi-elastic scattering (symbols). The momentum distribution of the incoming 8He beam is shown for comparison. The solid curves are the results from the simulation. The cyan (magenta) dotted line represents the upper (lower) limit of the 4He (proton) momentum expected from the simulation assuming a quasi-elastic scattering, and the orange line indicates the central beam momentum.
