M. N. Platonova, V. I. Kukulin
A principally new mechanism for the basic 2\pi-fusion reaction p + n --> d + (\pi\pi)_0 in the energy region T_p = 1.0-1.4 GeV is suggested. The mechanism is aimed to provide a non-contradictory explanation for the comprehensive experimental studies of this reaction in exclusive setting done recently at COSY-WASA. The basic assumption of the model proposed is the production of the I(J^P) = 0(3^+) dibaryon resonance D_03 in the pn collision. The interference of two decay channels of this resonance: D_03 --> d + {\sigma} --> d + (\pi\pi)_0 and D_03 --> D_12 + \pi --> d + (\pi\pi)_0 is shown to give a strong near-threshold enhancement in the (\pi\pi) invariant mass spectrum, which is well known as the ABC-effect. The {\sigma}-meson parameters found to reproduce the ABC-enhancement are in a general agreement with models which predict a chiral symmetry restoration at a high excitation energy and/or high density of matter, although they are essentially less than those accepted for the free {\sigma}-meson. So, this result might be considered as an indication of the (partial) chiral symmetry restoration in dense and excited quark matter.
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http://arxiv.org/abs/1211.0444
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