The A y puzzle and the nuclear force

Abstract

The nucleon-deuteron analyzing power A y in elastic nucleon-deuteron scattering poses a longstanding puzzle. At energies E lab below approximately 30MeV A y cannot be described by any realistic NN force. The inclusion of existing three-nucleon forces does not improve the situation. Because of recent questions about the 3 P J NN phases, we examine whether reasonable changes in the NN force can resolve the puzzle. In order to do this we investigate the effect on the 3 P J waves produced by changes in different parts of the potential (viz., the central force, tensor force, etc.), as well as on the 2-body observables and on A y . We find that it is not possible with reasonable changes in the NN potential to increase the 3-body A y and at the same time to keep the 2-body observables unchanged. We therefore conclude that the A y puzzle is likely to be solved by new three-nucleon forces, such as those of spin-orbit type, whichhave not yet been taken into account. PACS

Charge dependence of the nucleon-nucleon interaction

“…However, since the phase shifts in these states themselves are small, the relative magnitudes of the phase shift differences are not negligible and could have a noticable effect on some sensitive observables such as the analyzing power (A y ) in nucleondeuteron (nd) scattering [18] since this reaction blows up effects from triplet P waves [19]. Our microscopic predictions are, however, substantially smaller than what is needed to solve the nd A y puzzle [18,20].…”