ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?

TL;DR

This paper reports high-statistics measurements of the double pionic fusion reaction revealing a resonance linked to the ABC effect, characterized by a Lorentzian energy dependence and consistent with a specific resonance in $pn$ and $$ systems.

Contribution

First high-statistics measurement of the ABC effect in double pionic fusion, identifying a resonance with specific quantum numbers and energy dependence.

Findings

ABC effect associated with a Lorentzian energy dependence

Resonance with I(J^P)=0(3^+) identified in $pn$ and $$ systems

Data supports resonance interpretation of the ABC effect

Abstract

We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to d\pi^0\pi^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $\pi\pi$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $\Delta\Delta$ systems. Necessary further tests of the resonance interpretation are discussed.