With an effective Lagrangian approach, we analyze several N N → N N ππ channels by including various resonances with mass up to 1.72 GeV. For the channels with the pion pair of isospin zero, we confirm the dominance of N * (1440) → N σ in the near threshold region. At higher energies and for channels with the final pion pair of isospin one, we find large contributions from N * (1440) → ∆π, double-∆, ∆(1600) → N * (1440)π, ∆(1600) → ∆π and ∆(1620) → ∆π. There are also sizeable contributions from ∆ → ∆π, ∆ → N π, N → ∆π and nucleon pole at energies close to the threshold. We well reproduce the total cross sections up to beam energies of 2.2 GeV except for the pp → ppπ 0 π 0 channel at energies around 1.1 GeV and our results agree with the existing data of differential cross sections of pp → ppπ + π − , pp → nnπ + π + and pp → ppπ 0 π 0 which are measured at CELSIUS and COSY.

The newly measurement of production fractions of P c states by LHCb collaboration have put restriction on their branching ratios of J/ψp decay, thus constraining their photoproduction in γp → J/ψp reaction. We show the tension between LHCb results and the current experiments in search of P c photoproduction. We also find that the present information of branching ratios of P c → J/ψp has already confronted sharply with the models which study the nature of P c . * Corresponding author: daijianping@ihep.ac.cn P c (4312) + 4311.9 ± 0.7 +6.8 −0.6 9.8 ± 2.7 +3.7