Establishing the 40Ca(p,pα) Reaction at 392 MeV under Quasi-Free Scattering Conditions

The (Formula presented) reaction offers a direct means to probe preformed (Formula presented) -cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into (Formula presented) clustering, but quantitative comparison with microscopic cluster wave functions remained limited due to strong distortion effects. At higher energies, the reaction mechanism becomes simpler and the distorted-wave impulse approximation (DWIA) provides a more reliable framework for quantitative analysis. In the present work, the (Formula presented) Ca(Formula presented) reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and Large Acceptance Spectrometer at RCNP. Despite the small cross section in this energy region, the achieved resolution allowed clear separation of the ground and excited states of the residual (Formula presented) Ar nucleus, and corresponding momentum distributions were extracted. DWIA calculations using a Woods–Saxon (Formula presented) Ar bound-state wave function yielded an experimental spectroscopic factor of (Formula presented), consistent with the previous result at 101.5 MeV ((Formula presented)). This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision (Formula presented) measurements at several hundred MeV and highlights their potential as a quantitative probe of (Formula presented) clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems.