Speaker
Description
We study the two step sequential one pion production mechanism, $np(I=0)→π^{−}pp$, followed by the fusion reaction $pp→π^{+}d$, in order to describe the $np→π^{+}π^{−}d$ 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 $pp→π^{+}d$ 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.
