The pole structures of the X (1840) /X (1835) and the X (1880)

Whether the NN interaction could form a state or not is a long standing question, even before the observation of the pp threshold enhancement in 2003. The recent high statistic measurement in the J/ 3 (^+^-) channel would provide a good opportunity to probe the nature of the peak structures around the pp threshold in various processes. By constructing the NN interaction respecting chiral symmetry, we extract the pole positions by fitting the pp and 3 (^+^-) invariant mass distributions of the J/ p p and J/ 3 (^+^-) processes. The threshold enhancement in the pp invariant mass distribution is from the pole on the third Riemann sheet, which more couples to the isospin triplet channel. The broader structure in the 3 (^+^-) invariant mass comes from the pole on the physical Riemann sheet, which more couples to the isospin singlet channel. Furthermore, the large compositeness indicates that there should exit pp resonance based on the current experimental data. In addition, we also see a clear threshold enhancement in the nn channel, but not as significant as that in pp channel, which is useful and compared with further experimental measurement.