The Search and Study of Low-Mass Scalar Mesons in the Reaction np --> np Pi+Pi- at Pn = 5.20 Gev/c^2

TL;DR

This study investigates low-mass scalar mesons produced in neutron-proton collisions at 5.20 GeV/c, identifying nine new resonances with specific quantum numbers and proposing a phenomenological mass dependence.

Contribution

The paper reports the discovery of nine new scalar-isoscalar resonances in np collisions, with detailed quantum number measurements and a new mass dependence model.

Findings

Nine new resonances at specific masses with narrow widths.

Quantum numbers I^G(J^(PC))=0+(0++), consistent across resonances.

A phenomenological mass dependence for scalar mesons.

Abstract

Using irradiation of a 1-meter Hydrogen Bubble Chamber (LHE JINR) by a quasimonochromatic neutron beam with impulse Pn=(5.20 +/- 0.12)GeV/c produced after acceleration of deuterons in the synchrophasotron (LHE JINR) 2560 events of reaction np-->npPi+Pi- were selected. After supplementary sorting out the events where a secondary proton flies forward in the general c.m.s. of reaction in the effective mass spectrum of Pi+Pi- - combinations, there were nine peculiarities found out at masses 350, 408, 489, 579, 676, 762, 878, 1036, 1170 MeV/c^2 with experimental widths not more than several tens of MeV/c^2. The resonance effects grow too much after using an additional criterion - balance of the sum of the longitudinal impulse of Pi+ and Pi--mesons in the general c.m.s. of the reaction. Under these conditions the values of a standard derivation from the background are (5 - 7.5). The direct measurement of the spin of resonances was carried out. Also other quantum numbers were obtained. All of these peculiarities have a similar set of quantum numbers I^G(J^(PC))=0+(0++). This way the sequence of scalar-izoscalar resonances f0(SIGMA0) with masses in the range of M<M1200 MeV/c^2 are to be seen. There is no information about these resonances in the literature. The phenomenological dependence for the resonance mass from its number was found. This dependence covered not only resonances shown in this paper but also all those which are present in PDG tables with quantum numbers f0(SIGMA0) - mesons.