The researchers in Institute of Modern Physics, Chinese Academy of Sciences(IMP) analyzed the double -pion production in nucleon-nucleon collisions within an effective Lagrangian approach. Various resonances with mass up to 1.72 GeV listed in the Booklet of Particle Data Group were included in the model, and π-，Ρ- and η-meson exchange were considered. The calculated results indicated large contributions from N*(1440) and Δ(1232) in the close-to-threshold region and the important role of Δ(1600) and Δ(1620) above the beam energies of 1.5GeV so the achieved agreement with the data are reasonable.

The model found that the Ρ-meson exchange was very small, which was different from the previous non-relativistic Valencia model and supported by the recent data. The results provided important hints to the ABC effect and were meaningful to the future experimental project at COSY in Jülich, Germany and HIRFL-CSR in Lanzhou, China.

Based on the study of double-pion production in nucleon-nucleon collisions, the researchers gave a further analysis to the double-pion production in anti-nucleon-nucleon collisions. The role of N*(1440) in these reactions was first explored which was overlooked by previous experiment and theory. At the same time, the contributions of other resonances were studied. The researchers pointed out that anti-nucleon-nucleon collisions were shown to be complementary to the nucleon-nucleon collisions and even hold the advantage on some aspects. So the PANDA at FAIR in Germany can be an essential place for studying the properties of resonances and the data with (anti-)baryon in final states are worth analyzing.

The work has been published in Nuclear Physics A 861, 23 (2011) and Physical Review C 81, 065201 (2010).

Fig.1. The data of total cross sections of double-pion production in nucleon-nucleon collisions together with the model calculated contributions.(Image by IMP)

Fig.2. The data of total cross sections of double-pion production in anti-nucleon-nucleon collisions together with the model calculated contributions.(Image by IMP)