Resonances in the system of pi sup +pi sup - mesons from np -> np pi sup +pi- reaction at P sub n = 5.20 GeV/c: search, results of direct observations, interpretation

Ten resonances were found in the mass spectrum of the pi sup +pi sup - system based on 66075 events from the reaction np -> np pi sup +pi sup - in np interactions at P sub n = (5.20 +- 0.16) GeV/c in the 1-m HBC of JINR's LHE by using the criterion cos THETA* p > 0. These masses are the following: (347 +- 12), (418 +- 6), (511 +- 12), (610 +- 5), (678 +- 17), (757 +- 5), (880 +- 12), (987 +-12), (1133 +- 15), and (1285 +- 22) MeV/c sup 2; their excess above background is 2.9, 5.2, 3.5, 1.4, 2.0, 8.5, 4.8, 3.8, 5.2, and 6.0 S.D., respectively. The experimental widths of the resonances vary within the region from 16 to 94 MeV/c sup 2. Such effects were not found in pi sup -pi sup 0 combinations from the reaction np -> pp pi sup -pi 0. Therefore, it is necessary to attribute the value of isotopic spin I = 0 to the resonances found in the mass spectrum of the pi sup +pi- system. The spin was estimated for the most statistically provided resonances at masses of 418, 511 and 757 MeV/c sup 2. We determine with a high degree of confidence that J = 0 for the resonances at M sub R = 757 MeV/c sup 2 and M sub R = 418 MeV/c sup 2 and the most probable value of J = 0 for the resonance at M sub R = 511 MeV/c sup 2. Therefore, it can be affirmed that at least three states with quantum numbers of sigma sub 0 meson 0 sup + (0 sup + sup +) have been found at masses of 418, 511 and 757 MeV/c sup 2. The fact that low-mass sigma sub 0 mesons are glueballs is one of the possible interpretations. The comparison with the data of other papers has also been made