The two-step mechanism explaning the dibaryon “d ∗ (2380)” peak

In this talk we show that the two-step sequential one pion production mechanism, np(I = 0) → π −pp, followed by the fusion reaction pp → π +d, can explain the narrow peak identified with a “d ∗ (2380)” dibaryon in the np → π +π −d reaction with π +π − in I = 0. We demonstrate 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.