NN scattering with coupling: dibaryon resonances without “dibaryons”?

J. A. Niskanen

doi:10.1140/epja/s10050-024-01315-5

2024 Impact factor 2.8

Hadrons and Nuclei

Open Access

Eur. Phys. J. A (2024) 60: 109
https://doi.org/10.1140/epja/s10050-024-01315-5

Regular Article - Theoretical Physics

NN scattering with $N Δ$ $N\varDelta$ coupling: dibaryon resonances without “dibaryons”?

J. A. Niskanen^a

Helsinki Institute of Physics, PO Box 64, 00014, University of Helsinki, Finland

^a jouni.niskanen@helsinki.fi

Received: 19 December 2023
Accepted: 8 April 2024
Published online: 15 May 2024

Abstract

It is known that at their threshold intermediate two-baryon $N Δ$ $N\varDelta$ states can produce resonance-like structures in some isospin one states, often interpreted as more exotic manifest six-quark states. This paper applies the coupled-channel method to study vital details of the $N Δ$ $N\varDelta$ effect in isospin one NN scattering with interactions constrained to exclude the influence of such extraneous hypothetical particles in two respects. Firstly, the calculated phase parameters are fitted only below pion inelasticity, i.e. far below the region of “dibaryons”. Secondly, the strength of the $N N \to N Δ$ $NN \rightarrow N\varDelta$ transition is constrained to agree with the pion production reaction $N N \to d π$ $NN\rightarrow d\pi$ , fairly independent of the details of the pure “diagonal” NN potential and its effect practically as strong as the NN itself. The strongly angular momentum dependent ingredients and results may be considered as a necessary background for searches of any additional dibaryon effects. Optimal conditions for resonant $N Δ$ $N\varDelta$ appearances involve a decrease of the orbital angular momentum in the transition $N N \to N Δ$ $NN\rightarrow N\varDelta$ , as is the case in the $^{1} D_{2}$ $$^1D_2$$ and $^{3} F_{3}$ $$^3F_3$$ waves. Detailed complex phase shift results are further presented also for isospin one peripheral partial waves up to $J = 6$ $$J=6$$ , where, contrary to common prejudice, $N Δ$ $N\varDelta$ excitation is still found to be comparable to or even larger than one pion exchange.

© The Author(s) 2024

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