ABC effect as a signal of chiral symmetry restoration in hadronic collisions

TL;DR

This paper proposes a new mechanism involving a dibaryon resonance to explain the ABC effect observed in pn collisions, suggesting partial chiral symmetry restoration in dense hadronic matter.

Contribution

It introduces a novel model linking the ABC effect to dibaryon resonance decay channels, connecting experimental observations with chiral symmetry restoration theories.

Findings

The model reproduces the ABC enhancement in invariant mass spectra.

Parameters of the {\sigma} meson align with chiral symmetry restoration predictions.

The mechanism offers a unified explanation for recent experimental data.

Abstract

A new nonconventional mechanism for the basic 2{\pi}-fusion reaction pn --> d+({\pi}{\pi})_0 in the energy region T_p = 1.0-1.4 GeV is suggested. The mechanism is aimed at providing a consistent explanation for the comprehensive experimental studies of this reaction in exclusive setting done recently by the WASA-at-COSY Collaboration. The basic assumption of the model proposed is the production of the I(JP) = 0(3+) dibaryon resonance D03 in the pn collision. The interference of two decay channels of this resonance: D_03 --> d + {\sigma} --> d + ({\pi}{\pi})_0 and D_03 --> D_12 + {\pi} --> d + ({\pi}{\pi})_0 is shown to give a strong near-threshold enhancement in the {\pi}{\pi} invariant mass spectrum, which is well known as the ABC effect. The {\sigma}-meson parameters found to reproduce the ABC enhancement are in a general agreement with models which predict the chiral symmetry restoration at high excitation energy and/or high density of matter, although they are essentially less than those accepted for the free {\sigma} meson. So, this result might be considered as an indication of partial chiral symmetry restoration in dense and excited quark matter.