Search for dibaryon resonances in the reactions $dd\to ddππ$ and $pd \to pdππ$

TL;DR

The paper investigates the potential to observe isoscalar dibaryon resonances, notably $D_{03}(2380)$, in the reactions $pd\to pd\pi\pi$ and $dd\to dd\pi\pi$ at SPD NICA energies using a $t$-channel $\sigma$-exchange excitation of the deuteron to the $D_{03}$ state and its decays to $d\pi\pi$ via $D_{03}\to\sigma+d$ (with $\sigma\to\pi\pi$) or $D_{03}\to D_{12}\pi$, $D_{12}\to d\pi$, following the Platonova–Kukulin model. The cross sections are computed with matrix elements $M_{fi}$, phase-space integrals, and an isospin factor $C_T$, and the results are confronted with existing data on $pn\to d\pi^0\pi^0$ to fix resonance parameters. The findings show that $pd\to pd\pi\pi$ can reproduce the resonance position and magnitude around $\sqrt{s}\approx 2.38$ GeV (with some tension at higher energies) and that $dd\to dd\pi\pi$ is strongly suppressed by the deuteron form factor, offering a cleaner but experimentally challenging isoscalar probe. The work supports searching for isoscalar dibaryons in these channels at SPD NICA and outlines how the $pd$ channel may act as a subprocess within a broader $dd$ reaction framework using impulse approximation.

Abstract

The isoscalar dibaryon resonance $D_{03}(2380)$, discovered at WASA@COSY in the total cross section of the reaction $pn\to dπ^0π^0$ and in the elastic pn scattering in the energy range corresponding to the invariant mass of the pn system of 2380 MeV, can reveal itself in the $pd\to pdππ$ and $dd\to ddππ$ reactions at higher energies due to deuteron excitation in the $t$ channel. In this paper, the cross sections of these reactions are estimated based on the model of the reaction $pn\to dπ^0π^0$, proposed earlier by Platonova and Kukulin.

Figures (4)

• Figure 1: The mechanism of the deuteron excitation via the $\sigma$-meson exchange in the reactions $pd\to pd\pi\pi$ (left) and $dd\to dd\pi\pi$ (right).
• Figure 2: The differential cross section as a function of the invariant mass squared $M^2_{d\pi}$ in the reaction $pn \to d \pi^0\pi^0$ at the total energy $\sqrt{s_{pn}}=2.380$ GeV. The contribution of the $\sigma$-meson production mechanism is shown by dashed line, while the mechanism with intermediate dibaryon $D_{12}$ is shown by dashed-dotted line and the full line corresponds to the sum of $\sigma$ and $D_{12}$ mechanisms. The experimental data (circles) are taken from Ref.WASA-at-COSY:2011bjg.
• Figure 3: The distributions over the invariant mass $M_{d\pi\pi}$ in the reaction $pd\to pd \pi\pi$ at the proton beam kinetic energy 1.1 GeV ( a) and 1.4 GeV ( b). The results of calculation (full curves) according to mechanism in Fig. \ref{['fig-mech1']} (left panel) in comparison with experimental data ($\circ$) from Ref.Komarov:2018pry.
• Figure 4: The distributions over the invariant mass $M_{d\pi\pi}$ in the reaction $pd\to pd \pi\pi$ (upper panel) and $dd\to dd \pi\pi$ (down panel) calculated according to the mechanisms in Fig.\ref{['fig-mech1']} at different proton beam energy $T_p$ in $pd$- and deuteron beam energy $T_d$ in dd-collision (at the total energy $\sqrt{s_{dd}}$): (i) 1 -- $T_p =$ 2 GeV, 2 -- 4 GeV, 3 -- 7 GeV, 4 -- 10 GeV in the upper panel; (ii) 1, 2 -- $T_d=4$ GeV ( $\sqrt{s_{dd}}$= 5.4 GeV) , 3 -- 8 GeV ($\sqrt{s_{dd}}$= 6.64 GeV), 4 -- 14 GeV ($\sqrt{s_{dd}}$= 8.2 GeV), 5 -- 20 GeV ($\sqrt{s_{dd}}$= 9.44 GeV), in the down panel. All lines in the down panel are obtained with the deuteron form factor included, except the line 1, where the form factor is excluded.