Speaker
Description
Search for dibaryon resonances in two-nucleon systems has a long history (for review see [1]). At present as one of the most realistic candidate to the dibaryon resonance is considered the $D_{IJ}=D_{03}$ peak observed by WASA@COSY [2] in the total cross section of the reaction of two-pion production $pn\to d\pi^0\pi^0$, here $I$ is the isospin and $J$ is the total angular momentum of this resonance. The mass of the resonance is 2.380 GeV is close to the $\Delta\Delta$-threshold, but its width $\Gamma=70$ MeV is twice lower as compared to the width of the free $\Delta$-isobar. This narrow width is considered as the most serious indication to a non-hadronic, but most likely, quark content of the observed resonance state. The spin-parity of this resonance $J^P=3^+$ were established by polarized measurements. One possible mechanism of the reaction $pn\to d\pi^0\pi^0$ suggested in paper [3] involves sequential excitation and decay of two dibaryon resonances, $D_{03}(2380)$ and $D_{12}(2150)$.
Rather similar resonance structure was observed by ANKE@COSY in the differential cross section of the two-pion production reaction $pd\to pd \pi\pi$ at beam energies 0.8-2.0 GeV with high transferred momentum to the deuteron [4]. This kinematic conditions strongly differ from the quasi-free reaction studied in Ref. [2]. In distribution over the invariant mass $M_{d\pi\pi}$ of the final $d\pi\pi$ system the resonance peaks were observed at $M_{d\pi\pi}\approx 2.380$ GeV [4] that is the mass of the isoscalar two-baryon resonance $D_{IJ}=D_{03}$ . The widths of these peaks are by factor of $\sim 1.5$ larger than for the $D_{03}$ that can be caused by the isovector component of the final $\pi\pi$ system. In order to explain the observed resonance behavior of the reaction $pd\to pd \pi\pi$ we apply [5] the modified two-resonance model [3] with inclusion of the $\sigma$-meson exchange between the proton and deuteron. Two variants of the $\sigma$-meson interaction are considered and one of them with assumption on the partial restoration of the chiral symmetry [3] and another one without it. Neglecting the contribution of the isovector state of the final $\pi\pi$ pair, we show that it is possible to explain simultaneously the shape and absolute value of the measured in Ref. [2] the $M_{d\pi}$ distribution in the cross section of the reaction $pn\to d\pi^0\pi^0$ and some properties of the reaction $pd\to pd \pi\pi$, namely, position of the resonance peak in the cross section and roughly its absolute value at $T_p=1.1-1.4$ GeV. The shape of the distribution over the invariant mass of the final $\pi\pi$ system in the reaction $pd\to pd \pi\pi$ is reproduced only qualitatively.
[1] H.Clement, Prog. Part. Nucl. Phys. ${\bf 93}$ (2017) 195.
[2] P.Adlarson {\it et al.}, Phys. Rev. Lett. ${\bf 106}$ (2011) 242302 .
[3] M.N.Platonova, V.I.Kukulin, Phys. Rev. C ${\bf 87}$ (2013) 025202;
Nucl. Phys. ${\bf A 946}$ (2016)117 .
[4] V.I.Komarov et al., Eur. Phys. J. ${\bf A 54}$ (2018) 206.
[5] N.Tursunbayev, Yu.Uzikov, Springer Proc. Phys. ${\bf 238}$ (2020) 467.
