Pion production in nucleon-nucleon collisions and the issue of dibaryons

T Skorodko,H Clement,M Bashkanov,A Wrońska,A Magiera,W Przygoda

doi:10.1051/epjconf/201919901015

Abstract

Pion production in nucleon-nucleon collisions is tightly connected with the issue of dibaryons. After having established the existence of the narrow dibaryon resonance d* (2380) with I(JP) = 0(3+) by two-pion production and elastic proton-neutron scattering experiments, the discussion focuses now on its structure, whether it is a dilute molecular-like or a compact hexaquark object. These scenarios are confronted with experimental branching ratios and other observables. New WASA data for the pp → ppπ+π− reaction give evidence for the existence of an isotensor ΔN threshold state with JP = 1+ as calculated recently by Gal and Garcilazo and predicted earlier by Dyson and Xuong. New ANKE results suggest the dibaryon spectrum to be richer than expected.

Highlights

Since pions are the lowest-mass messengers of subnucleonic degrees of freedom, the production of one or more pions in nucleon-nucleon collision processes is outstandingly suited to search for resonances in the two-baryon system
For a detailed review on this and other dibaryon searches see Ref. [1]. It took until the beginning of this millennium, when the first non-trivial, narrow dibaryon resonance could be established by WASA at CELSIUS and COSY
Reexamining the pp → ppπ+π− reaction at higher beam energies we find evidence for an isotensor dibaryon resonance near the ΔN threshold

Summary

Introduction

Since pions are the lowest-mass messengers of subnucleonic degrees of freedom, the production of one or more pions in nucleon-nucleon collision processes is outstandingly suited to search for resonances in the two-baryon system. This result is in line with the expectation that during the decay process d∗(2380) → ΔΔ the distance between the two Δs increases eliminating the Fermi motion and putting that way mass and width of the Δs back to their asymptotically correct values From this findings it follows that the small total width of d∗(2380) calculated in the Fermi motion scenario inside the confinement region is NOT transmitted to the outside and does not explain the observed narrow width of d∗(2380) as speculated in the Fermi motion scenario

Evidence for the isotensor dibaryon resonance D21

Findings

Summary and outlook