Search for and study of low-mass scalar mesons in reaction np → npπ+π− at neutron beam momentum P n = (5.20 ± 0.12) GeV/c

Abstract

We present the results of a search for and study of the resonance effects in the system of π+π− from the reaction np → npπ+π− at the momentum of quasi-monochromatic neutrons Pn = (5.20 ± 0.12) GeV/c from the data obtained in an exposure of the 1-m hydrogen bubble chamber of Veksler and Baldin Laboratory of High Energies, Joint Institute for Nuclear Research (VBLHE JINR). After the supplementary selection of the events where a secondary proton was emitted in the forward hemisphere in the general c.m.s. of the reaction (cosθ*p> 0) in the effective mass spectrum of π+π− combinations, we found nine peculiarities at the masses (350 ± 3), (408 ± 3), (489 ± 3), (579 ± 5), (676 ± 7), (762 ± 11), (878 ± 7), (1036 ±13), and (1170 ± 11) MeV/c2 with experimental widths of no more than several tens of MeV/c2. We carried out a direct measurement of the spins of resonances and also obtained other quantum numbers. All of these peculiarities have a similar set of quantum numbers IG(JPC) = 0+ (0++). We investigated a sequence of scalar-isoscalar resonances f0(σ0) with masses in the range M ≤ 1200 MeV/c2. We found a phenomenological dependence of the resonance mass on its number. This dependence covered not only the resonances shown in this paper, but also those present in PDG tables with quantum numbers of f0(σ0) mesons.