Study of the pd(dp) -> 3He pi pi reactions close to threshold

TL;DR

This paper presents new experimental data on the pd -> 3He pi+ pi- reaction near threshold, showing suppressed low-energy pi+ pi- production and exploring possible underlying mechanisms.

Contribution

It provides novel measurements of the reaction close to threshold and analyzes the suppression of low-energy pion pairs with potential explanations.

Findings

No enhancement at low excitation energies in pi+ pi- system

Data largely suppressed compared to phase space

Exploration of p-wave and two-step process influences

Abstract

New experimental data on the pd -> 3He pi+ pi- reaction obtained with the COSY-MOMO detector below the three-pion threshold are presented. The reaction was also studied in inverse kinematics with a deuteron beam and the higher counting rates achieved were especially important at low excess energies. The comparison of these data with inclusive pd -> 3He+X rates allowed estimates also to be made of pi0 pi0 production. The results confirm our earlier findings that close to threshold there is no enhancement at low excitation energies in the pi+ pi- system, where the data seem largely suppressed compared to phase space. Possible explanations for this behavior, such as strong p- waves in the pi+pi- -system or the influence of two-step processes, are explored.