Relatore
Descrizione
We study the two step sequential one pion production mechanism, $np(I = 0) \toπ^− pp$, followed by the fusion reaction $pp \to π^+ d$, in order to describe the $np \to π^+ π^− d$ reaction with $π^+ π^−$ in $I = 0$, where a narrow peak, so far identified with a “d(2380)” dibaryon, has been observed. We find that the second step $pp \to π^+ d$ is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation of the peak without invoking a dibaryon explains why the peak is not observed in other reactions where it
has been searched for.
