TheAypuzzle 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 numbers:

Non-relativistic Neutron Deuteron Scattering

“…After obtaining the numerical solution for the amplitude we are able to calculate any parity conserving observable of interest. One of the most important observables is A y , which measures the asymmetry between the cross sections induced by nucleons of opposite transverse spin polarization on an unpolarized deuteron target [7]:Varying the N 3 LO coefficients within the EFT / π uncertainty gives the results in Fig 3, which shows good agreement with the differential cross section and reasonable agreement with A y for a variety of energies. We can also pursue the calculation to higher orders to attempt to improve the agreement.…”

“…After obtaining the numerical solution for the amplitude we are able to calculate any parity conserving observable of interest. One of the most important observables is A y , which measures the asymmetry between the cross sections induced by nucleons of opposite transverse spin polarization on an unpolarized deuteron target [7]:…”

Proton-He3elastic scattering at low energies

“…Looking at N N scattering data only, this possibility does not seem to be ruled out [29,30]. However, after taking theoretical constraints into account [31], this solution was considered unlikely, and has been confirmed by recent calculations which show that this puzzle is not solved even when new N N potentials derived from effective field theory are used [8,32].…”

Benchmark calculations for polarization observables in three-nucleon scattering

“…The aim of the present article is to demonstrate that extremely accurate numerical results can be achieved. These two 3N observables A y and iT 11 are of special interest, since present theoretical descriptions are about 30% off the experimental data in the low energy region and up to now no explanation has been found for the discrepancy [9,[12][13][14].…”