Three-body forces and shell structure in calcium isotopes

Understand

Understanding and predicting the formation of shell structure from nuclear forces is a central challenge for nuclear physics.

• While the magic numbers N=2,8,20 are generally well understood, N=28 is the first standard magic number that is not reproduced in microscopic theories with two-nucleon forces.
• In this Letter, we show that three-nucleon forces give rise to repulsive interactions between two valence neutrons that are key to explain 48Ca as a magic nucleus, with a high 2+ excitation energy and a concentrated magnetic dipole transition strength.
• The repulsive three-nucleon mechanism improves the agreement with experimental binding energies.