An empirical model of low-energy np scattering: Insights beyond ERT

TL;DR

This paper introduces an empirical model of low-energy neutron-proton scattering involving an off-shell dibaryon, providing mechanistic insights beyond the shape-independent effective range theory, which only fits data without revealing underlying processes.

Contribution

The model offers a novel mechanistic perspective on np scattering by incorporating an off-shell dibaryon and vertex corrections, extending understanding beyond traditional effective range theory.

Findings

Model matches np scattering data within errors up to 3 MeV

Provides insight into the signs of scattering lengths based on wavefunction symmetries

Suggests mechanisms involving off-shell dibaryons and pion exchange

Abstract

A model is presented of s-wave np elastic scattering as proceeding through an intermediate, off-shell dibaryon d*, with corrections to the npd vertex and d* propagator. The model relies on plausible conjectures and hypotheses to match identically the form of the simple amplitude given by the shape-independent effective range theory (SI ERT), which exactly describes the extant np elastic data (within errors) to at least 3 MeV. The result provides insight into the mechanisms involved in np scattering, which go beyond what ERT can reveal because ERT is a product of wave-mechanics and is therefore generally independent of mechanism. For example, in this model, the signs of the triplet and singlet scattering lengths are determined by the (opposite) spatial symmetries of the triplet and singlet np wavefunctions and pion exchange in the vertex corrections.