The nuclear structure of $^{46}Ar$: A study of the direct proton-transfer\\ $^{46}Ar(^{3}He,{d})^{47}K$ reaction.

Direct reactions represent a unique mechanism to investigate the nuclear-structure properties and the nature of single-particle states of nuclei along shell closures. In this contribution, the $^{46}Ar(^{3}He, {d})^{47}K$ proton-transfer reaction is proposed to shed light on the properties of the ground state of the radioactive neutron-rich $^{46}Ar$ isotope. The measurement, performed at the SPIRAL 1 facility in GANIL, France with a post-accelerated radioactive $9 {MeV/{u}} ^{46}Ar$ beam impinging on a high-density cryogenic $^{3}He$ target, aimed at quantifying the transfer cross-section to the $3/2^{+}$ level relative to the $1/2^{+}$ ground state in $^{47}K$. The experimental evidence indicates a substantially suppressed $L=2$ transfer to the first excited state of $^{47}K$, at odds with shell-model calculations that predict the $s^{1/2}$ and $d^{3/2}$ orbitals as almost degenerate and not entirely occupied. The results will be also discussed in the framework of $ab initio$ and mean-field calculations. In these theoretical results, the low occupancy of the $s^{1/2}$ orbital, in agreement with the high relative spectroscopic factor measured, implies a central depletion of the proton wave function. This contribution presents the first experimental evidence of this phenomenon in $^{46}Ar$.