Dibaryon Resonances Research Articles

On sequential single-pion production in double-pionic fusion

Recently a two-step process has been proposed for the double-pionic fusion to deuterium pn(I=0)→dπ+π−. Its calculation is solely based on total cross section data for the two sequential single-pion production steps pn(I=0)→ppπ− followed by pp→dπ+. Though this sequential process was aimed to explain the dibaryon resonance d⁎(2380) peak in double-pionic fusion, we demonstrate that this is not the case. It rather fits to a possible broad bump at 2.31 GeV in the energy dependence of the pn→dπ0π0 reaction, which was recently interpreted as a consequence of dibaryonic excitations in isoscalar single-pion production.

Dibaryon Resonances and Three-Body Forces in Large-Angle pd Elastic Scattering at Intermediate Energies

Dibaryon Resonances and Three-Body Forces in Large-Angle pd Elastic Scattering at Intermediate Energies

Resonant behavior of the pp→{pp}sπ0 reaction at the energy s=2.65GeV

We report on measurements of the differential cross section $d\sigma/d\Omega$ in the energy region of $\sqrt{s}$ = 2.5-2.9 GeV of the reaction $pp \to \{pp\}_s \pi^0$ where $\{pp\}_s$ is a $^1\!S_0$ proton pair. The experiment has been performed with the ANKE spectrometer at COSY-J\"ulich. The data reveal a peak in the energy dependence of the forward $\{pp\}_s$ differential cross section at the energy $\sqrt{s}$ = 2.65 GeV with the width $\Gamma$ = 0.26 GeV, and also the cross section slope changes its sign in the region of the observed peak. This is an indication for the excitation of a new $D(2650)$ resonant state, that may be a dibaryon resonance system consisting of two excited baryons $\Delta(1232)$ and $N^*(1440)$.

Possibility of dibaryon formation near the N*(1440)N threshold: Reexamination of isoscalar single-pion production

The isoscalar single-pion production exhibits a broad bump in the energy dependence of the total cross section, which does not correspond to the usual opening of the ${N}^{*}(1440)$ production channel with subsequent pion decay. We reevaluate the current database and investigate whether the observed bump structure with a width of about 150 MeV points to the formation of dibaryon states with $I({J}^{P})=0({1}^{+})$ and $0({1}^{\ensuremath{-}})$ near the ${N}^{*}(1440)N$ threshold. This situation would be similar to the situation at the $\mathrm{\ensuremath{\Delta}}(1232)N$ threshold, where the signature of a number of dibaryonic resonances has been found.

Dibaryon resonances and short-range NN interaction* *The work has been partially supported by RFBR, grants Nos. 19-02-00011 and 19-02-00014. M.N.P. also appreciates support from the Foundation for the Advancement of Theoretical Physics and Mathematics “BASIS”

The dibaryon concept for nuclear force is presented, assuming that the attraction between nucleons at medium distances is mainly due to the s-channel exchange of an intermediate six-quark (dibaryon) state. To construct the respective NN interaction model, a microscopic six-quark description of the NN system is used, in which symmetry aspects play a special role. It is shown that the NN interaction in all important partial waves can be described by the superposition of long-range t-channel one-pion exchange and s-channel exchange by an intermediate dibaryon. The model developed in this study provides a good description of both elastic phase shifts and inelasticities of NN scattering in all S, P, D, and F partial waves at energies from zero to 600–800 MeV and even higher. The parameters of the intermediate six-quark states, corresponding to the best fit of NN scattering data, are found to be consistent with the parameters of the known dibaryon resonances in those NN partial configurations, where their existence has been experimentally confirmed. Predictions for new dibaryon states are given as well.

Isospin symmetry breaking in double-pion production in the region of d*(2380) and the scalar σ meson

The first attempt is made to provide a quantitative theoretical interpretation of the WASA-at-COSY experimental data on the basic double-pion production reactions $pn\ensuremath{\rightarrow}d{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ and $pn\ensuremath{\rightarrow}d{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ in the energy region ${T}_{p}=1--1.3\text{ }\text{ }\mathrm{GeV}$ [Adlarson et al., Phys. Lett. B 721, 229 (2013)]. The data are analyzed within a model based on the production and decay of an intermediate $I({J}^{P})=0({3}^{+})$ dibaryon resonance ${\mathcal{D}}_{03}$ [also denoted as ${d}^{*}(2380)$]. The observed decrease of the near-threshold enhancement (the so-called ABC effect) in the reaction $pn\ensuremath{\rightarrow}d{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ in comparison to that in the reaction $pn\ensuremath{\rightarrow}d{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ is explained (at least partially) to be due to isospin symmetry violation in the two-pion decay of an intermediate near-threshold scalar $\ensuremath{\sigma}$ meson emitted from the ${\mathcal{D}}_{03}$ dibaryon resonance under conditions of partial chiral symmetry restoration.

P -wave dibaryon resonances in pp elastic scattering and near-threshold pion production

It is demonstrated within the dibaryon-induced model for $NN$ interaction that $pp$ scattering in $P$ waves is governed mainly by the production of the intermediate dibaryon resonances. Two dibaryon resonances with a mass of about 2200 MeV discovered recently by the ANKE-COSY Collaboration are shown to determine both elastic $pp$ phase shifts and inelasticities in the ${^{3}P}_{0}$ and ${^{3}P}_{2}$--${^{3}F}_{2}$ channels from zero energy up to ${T}_{p}=0.7--0.9\text{ }\mathrm{GeV}$. It is also demonstrated clearly that the ${^{3}P}_{0}$ dibaryon plays a decisive role in near-threshold neutral pion production in $pp$ collisions which is poorly understood to date. The missing dibaryon contribution is found to be the very possible reason for the failure of traditional approaches to explain near-threshold ${\ensuremath{\pi}}^{0}$ production.

D⁎(2380) dibaryon from lattice QCD

The ΔΔ dibaryon resonance d⁎(2380) with (JP,I)=(3+,0) is studied theoretically on the basis of the 3-flavor lattice QCD simulation with heavy pion masses (mπ=679,841 and 1018 MeV). By using the HAL QCD method, the central Δ-Δ potential in the S37 channel is obtained from the lattice data with the lattice spacing a≃0.121 fm and the lattice size L≃3.87 fm. The resultant potential shows a strong short-range attraction, so that a quasi-bound state corresponding to d⁎(2380) is formed with the binding energy 25-40 MeV below the ΔΔ threshold for the heavy pion masses. The tensor part of the transition potential from ΔΔ to NN is also extracted to investigate the coupling strength between the S-wave ΔΔ system with JP=3+ and the D-wave NN system. Although the transition potential is strong at short distances, the decay width of d⁎(2380) to NN in the D-wave is kinematically suppressed, which justifies our single-channel analysis at the range of the pion mass explored in this study.

Nature of $$\varvec{S}$$-wave $$\varvec{NN}$$ interaction and dibaryon production at nucleonic resonance thresholds

Phase shifts and inelasticity parameters for $NN$ scattering in the partial-wave channels ${}^3S_1$--${}^3D_1$ and ${}^1S_0$ at energies $T_{\rm lab}$ from zero to about 1 GeV are described within a unified $NN$ potential model assuming the formation of isoscalar and isovector dibaryon resonances near the $NN^*(1440)$ threshold. Evidence for these near-threshold resonances is actually found in the recent WASA experiments on single- and double-pion production in $NN$ collisions. There, the excitation of the Roper resonance $N^*(1440)$ exhibits a structure in the energy dependence of the total cross section, which corresponds to the formation of dibaryon states with $I(J^\pi)=0(1^+)$ and $1(0^+)$ at the $NN^*(1440)$ threshold. These two $S$-wave dibaryon resonances may provide a new insight into the nature of the strong $NN$ interaction at low and intermediate energies.

Differential cross sections for neutron-proton scattering in the region of the d*(2380) dibaryon resonance

Differential cross sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized n⃗p scattering performed in the energy region of the d*(2380) dibaryon resonance covering the range of beam energies Tn=0.98−1.29 GeV (s=2.32−2.44 GeV). The experiment was carried out with the WASA-at-COSY setup having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp→np+pspectator. In this way the np differential cross section σ(Θ) was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power Ay(Θ) measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled D33−G33 waves.Received 3 April 2020Accepted 9 June 2020DOI:https://doi.org/10.1103/PhysRevC.102.015204Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNucleon induced nuclear reactionsNucleon-nucleon interactionsParticle interactionsPhysical SystemsBaryonsHadronsParticles & FieldsNuclear Physics

Role of the d⁎(2380) dibaryon in NN interaction

It is demonstrated for the first time that the dibaryon resonance d⁎(2380) discovered reliably in the numerous experiments at the WASA@COSY facility (Jülich FZ) determines almost completely (when supplemented with the peripheral one-pion exchange) NN scattering phase shifts and inelasticities in the coupled partial-wave channels D33–G33 not only near the resonance position, but also in a broad energy range from zero up to about 1 GeV.

To the Nature of Nuclear Force

It has been shown for the first time that $NN$ interaction, at least in some partial waves, can be quantitatively described by the superposition of a long-range one-pion exchange and a short-range mechanism based on the complex pole in the $NN$ potential corresponding to the dibaryon resonance in this partial wave. For the partial waves $^3P_2$, $^1D_2$, $^3F_3$ and $^1S_0$ the parameters of the complex poles that give the best description of the elastic and inelastic phase shifts of $NN$ scattering are very close to the empirical parameters of the corresponding isovector dibaryon resonances detected experimentally. Based on the results obtained, a general conclusion is made about the nature of nuclear force at medium and small internucleon distances.

Resonance d*(2380) and higher isospin states

A new isoscalar state in the two-baryon system with mass 2380 MeV and width 80 MeV denoted now d*(2380) has been detected in the experiments at the Juelich Cooler Synchrotron (COSY). Existence or influence of states with higher isospin is a subject of the experiment for studing of the π+π− production in pp collisions. Calculations taking into account isotensor dibaryon resonance in the ΔN with I(Jp) = 2(1+) provide a good description of the pp → ppπ+π− total and differential cross sections.

Examination of the production of an isotensor dibaryon in the pp→ppπ+π− reaction

Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 1.08 - 1.36$ GeV ($\sqrt s$ = 2.35 - 2.46 GeV), which includes the regions of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong and more recently calculated by Gal and Garcilazo.

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.

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.

Charmed dibaryon resonances in the potential quark model

Charmed dibaryon states with the spin-parity [Formula: see text], and [Formula: see text] are predicted for the two-body [Formula: see text] ([Formula: see text], [Formula: see text], or [Formula: see text]) systems. We employ the complex scaling method for the coupled channel Hamiltonian with the [Formula: see text]-CTNN potentials, which were proposed in our previous study. We find four sharp resonance states near the [Formula: see text] and [Formula: see text] thresholds. From the analysis of the binding energies of partial channel systems, we conclude that these resonance states are Feshbach resonances. We compare the results with the [Formula: see text] resonance states in the heavy quark limit, where the [Formula: see text] and [Formula: see text] thresholds are degenerate, and find that they form two pairs of the heavy-quark doublets in agreement with the heavy quark spin symmetry.

Non-strange dibaryons studied in the γd → π0π0d reaction

Coherent double neutral-pion photoproduction on the deuteron, γd→π0π0d, has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the γd center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free π0π0 production with deuteron coalescence. In π0d invariant-mass distributions, a clear peak is observed at 2.14±0.01 GeV/c2 with a width of 0.09±0.01 GeV/c2. The spin-parity of this state is restricted to 1+, 2+ or 3− from the angular distributions of the two π0s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV/c2. The 2+ assignment is consistent with the theoretically predicted D12 state, and also with the energy dependence of the πd partial-wave amplitude P23 for the π±d→π±d and π+d→pp reactions.

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.

Isotensor Dibaryon in the pp→ppπ^{+}π^{-} Reaction?

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} reaction have been carried out at WASA@COSY by means of pd collisions at T_{p}=1.2 GeV. Total and differential cross sections have been extracted covering the energy region T_{p}=1.08-1.36 GeV, which is the region of N^{*}(1440) and Δ(1232)Δ(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor ΔN dibaryon resonance with I(J^{P})=2(1^{+}) produced associatedly with a pion is able to overcome these deficiencies.