The $D_{03}(2380)$ dibaryon resonance excitation in the $pd\to pd\pi\pi$ reaction.

The recent ANKE@COSY data on the differential cross section of reaction pd \to pd\pi\pipd→pdππ demonstrate a peak at invariant mass of the final d\pi\pidππ system 2.38~GeV2.38GeV, that corresponds to the isoscalar J^P = 3^+JP=3+ dibaryon D_{03}D03, and the enhancement in the distribution over the invariant mass of two final pions. The two-resonance model involving the tt-channel \sigmaσ-meson exchange between the proton and deuteron in the subprocess pd\to pD_{03}pd→pD03 and the sequential decays D_{03}\to D_{12}+\piD03→D12+π and D_{12}\to d +\piD12→d+π was applied to describe the shapes of these distributions with the lowest orbital angular momenta in the corresponding vertices. A possible role of higher orbital momenta in those vertices is studied here.

Pion production in nucleon-nucleon collisions and the issue of dibaryons

Pion production in nucleon-nucleon collisions is tightly connected with the issue of dibaryons. After having established the existence of the narrow dibaryon resonance d* (2380) with I(JP) = 0(3+) by two-pion production and elastic proton-neutron scattering experiments, the discussion focuses now on its structure, whether it is a dilute molecular-like or a compact hexaquark object. These scenarios are confronted with experimental branching ratios and other observables. New WASA data for the pp → ppπ+π− reaction give evidence for the existence of an isotensor ΔN threshold state with JP = 1+ as calculated recently by Gal and Garcilazo and predicted earlier by Dyson and Xuong. New ANKE results suggest the dibaryon spectrum to be richer than expected.

Reaction of two pion production pd → pdππ in the resonance region

The ANKE@COSY data on the reaction of two-pion production in the GeV region are analyzed within the theoretical model by Platonova and Kukulin. The model includes excitation of the dibaryon resonance DIJ = D03(2380) with the spin J = 3 and isospin I = 0 observed by the WASA@COSY in the reaction pn → dπ0π0, and its decay D03 → D12 + π → d + π + π, where D12(2150) is another dibaryon resonance. Distributions on the invariant masses of the final dππ and ππ systems are calculated.

Study of d∗(2380) resonance in a chiral constituent quark model

Studies on newly observed dibaryon resonance [Formula: see text] ([Formula: see text]) with a compact structure in recent years are reviewed. In terms of a dynamical calculation with a chiral constituent quark model by using Resonating Group Method, the general characteristics of this resonance, like its mass, binding energy, root-mean-square radius, as well as, its strong double pion decays of [Formula: see text] and [Formula: see text], its strong single pion decays of [Formula: see text], and its electromagnetic form factors, are given and compared with the experimental data. It is shown that the compact hexaquark dominant structure might be a reasonable interpretation for this dibaryon resonance and the charge distribution might be a new observable to judge different theoretical assumptions for its structure. Moreover, possible experimental tests are also discussed briefly.