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.

With an effective Lagrangian approach, we give a full analysis on the NN → NNππ and pp → pnπ + reactions for proton beam energy from 1 to 1.5 GeV. The results are very consistent with the experiment data from CELSIUS, KEK, COSY, and so on. Based on these results, we consider theNN →NNππ andpp →pnπ + for proton beam energy up to 4 GeV. Compare to the pp collisions, there are many benefits to study N * resonances in these two reactions. And for the high proton beam energy up to 15 GeV, we consider some new resonances with hidden charm which are definitely beyond three constituent quarks model in thepp →ppJ/ψ andpp →ppη c , where there are very nice places to find these new N * cc . The predicted results aboutpp collisions can be looked for at the forthcoming PANDA/FAIR experiments.

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