Charge radii of exotic potassium isotopes challenge nuclear theory and the magic character of N = 32

Nuclear charge radii are sensitive probes of different aspects the nucleon-nucleon interaction and bulk properties nuclear matter; thus, they provide a stringent test challenge for theory. The calcium region has been particular interest, as experimental evidence suggested new magic number at $N = 32$ [1-3], while unexpectedly large increases in [4,5] open questions about evolution size neutron-rich systems. By combining collinear resonance ionization spectroscopy method with $\beta$-decay detection, we were able to extend measurement potassium ($Z =19$) isotopes up exotic $^{52}$K ($t_{1/2}$ 110 ms), produced minute quantities. Our work provides first beyond region, revealing no signature character this neutron number. results interpreted two state-of-the-art theories. For time, long sequence could be calculated coupled-cluster calculations based on newly developed interactions. strong increase 28$ is not well captured by these calculations, but reproduced Fayans density functional theory, which, however, overestimates odd-even staggering effect. These findings highlight our limited understanding systems, expose pressing problems that present some best current models