Unitary Coupled-channels Model Research Articles

Three-body unitary coupled-channel approach to radiative J/ψ decays and η(1405/1475)

Recent BESIII data on radiative J/ψ decays from ∼1010 J/ψ samples should significantly advance our understanding of the controversial nature of η(1405/1475). This motivates us to develop a three-body unitary coupled-channel model for radiative J/ψ decays to three-meson final states of any partial wave (JPC). Basic building blocks of the model are bare resonance states such as η(1405/1475) and f1(1420), and πK, KK¯, and πη two-body interactions that generate resonances such as K*(892), K0*(700), and a0(980). This model reasonably fits KSKSπ0 Dalitz plot pseudodata generated from the BESIII’s JPC=0−+ amplitude for J/ψ→γKSKSπ0. The experimental branching ratios of η(1405/1475)→ηππ and η(1405/1475)→γρ relative to that of η(1405/1475)→KK¯π are simultaneously fitted. Our 0−+ amplitude is analytically continued to find three poles, two of which correspond to η(1405) on different Riemann sheets of the K*K¯ channel, and the third one for η(1475). This is the first pole determination of η(1405/1475) and, furthermore, the first-ever pole determination from analyzing experimental Dalitz plot distributions with a manifestly three-body unitary coupled-channel framework. Process-dependent ηππ, γπ+π−, and πππ lineshapes of J/ψ→γ(0−+)→γ(ηππ), γ(γρ), and γ(πππ) are predicted, and are in reasonable agreement with data. A triangle singularity is shown to play a crucial role to cause the large isospin violation of J/ψ→γ(πππ). Published by the American Physical Society 2024

\(\sigma (500)\) Resonance Pole Positions as a~Function of \(m_\pi \): Analysis with a Unitary Coupled-channel Model

\(\sigma (500)\) Resonance Pole Positions as a~Function of \(m_\pi \): Analysis with a Unitary Coupled-channel Model

Exploratory study of possible resonances in heavy meson - heavy baryon coupled-channel interactions**Supported by DFG and NSFC through funds provided to the Sino-German CRC 110 “Symmetry and the Emergence of Structure in QCD” (NSFC 11621131001, DFG TR110), as well as an NSFC fund (11647601). The work of UGM was also supported by the CAS President’s International Fellowship Initiative (PIFI) (2017VMA0025)

We use a unitary coupled-channel model to study the interactions. In our calculation, SU(3) flavor symmetry is applied to determine the coupling constants. Several resonant and bound states with different spin and parity are dynamically generated in the mass range of the recently observed pentaquarks. The approach is also extended to the hidden beauty sector to study the interactions. As the b-quark mass is heavier than the c-quark mass, there are more resonances observed for the interactions and they are more tightly bound.

Leptonic widths of high ψ -resonances in a unitary coupled-channel model

The leptonic widths of high $\ensuremath{\psi}$-resonances are calculated in a coupled-channel model with unitary inelasticity, where analytical expressions for the mixing angles between $(n+1){^{3}S}_{1}$ and $n{^{3}D}_{1}$ states and probabilities ${Z}_{i}$ of the $c\overline{c}$ component are derived. These factors depend on energy (mass) and can be different for $\ensuremath{\psi}(4040)$ and $\ensuremath{\psi}(4160)$. However, our calculations give a small difference between the mixing angles, $\ensuremath{\theta}(\ensuremath{\psi}(4040))=(2{8}_{\ensuremath{-}2}^{+1})\ifmmode^\circ\else\textdegree\fi{}$ and $\ensuremath{\theta}(\ensuremath{\psi}(4160))=(2{9}_{\ensuremath{-}3}^{+2})\ifmmode^\circ\else\textdegree\fi{}$, and $\ensuremath{\sim}10%$ difference between the probabilities ${Z}_{1}(\ensuremath{\psi}(4040))=0.8{5}_{\ensuremath{-}0.02}^{+0.05}$ and ${Z}_{2}(\ensuremath{\psi}(4160))=0.79\ifmmode\pm\else\textpm\fi{}0.01$. It provides the leptonic widths ${\mathrm{\ensuremath{\Gamma}}}_{ee}(\ensuremath{\psi}(4040))=\phantom{\rule{0ex}{0ex}}(1.0\ifmmode\pm\else\textpm\fi{}0.1)\text{ }\text{ }\mathrm{keV}$ and ${\mathrm{\ensuremath{\Gamma}}}_{ee}(\ensuremath{\psi}(4160))=(0.62\ifmmode\pm\else\textpm\fi{}0.0.07)\text{ }\text{ }\mathrm{keV}$ in agreement with experiment; for $\ensuremath{\psi}(4415)$ the value ${\mathrm{\ensuremath{\Gamma}}}_{ee}(\ensuremath{\psi}(4415))=(0.66\ifmmode\pm\else\textpm\fi{}0.06)\text{ }\text{ }\mathrm{keV}$ is obtained, while for the missing resonance $\ensuremath{\psi}(4510)$, we predict its mass, $M(\ensuremath{\psi}(4500))=(4512\ifmmode\pm\else\textpm\fi{}2)\text{ }\text{ }\mathrm{MeV}$, and ${\mathrm{\ensuremath{\Gamma}}}_{ee}(\ensuremath{\psi}(4510))=(0.68\ifmmode\pm\else\textpm\fi{}0.14)\text{ }\text{ }\mathrm{keV}$.

N AND Δ HIDDEN-CHARM RESONANCES WITH HEAVY-QUARK SPIN SYMMETRY

We study N and Δ hidden-charm baryon resonances that are generated dynamically from the s-wave interaction of pseudoscalar and vector mesons with 1/2+ and 3/2+ baryons. We use a unitary coupled-channels model that fulfills heavy-quark spin symmetry and respects spin-flavor symmetry in the light sector. We predict seven N-like and five Δ-like states with masses around 4 GeV, most of them as bound states. Some of these states form heavy-quark spin multiplets, which are almost degenerate in mass.

Odd-parity Dynamically Generated Baryon Resonances with Beauty Flavor

We study baryon resonances with heavy flavor in a molecular approach, thus as dynamically generated by baryon-meson scattering. This is accomplished by using a unitary coupled-channel model taking, as bare interaction, the extension of the Weinberg-Tomozawa SU(3) Lagrangian. A special attention is payed to the inclusion of heavy-quark spin symmetry and to the study of the generated baryon resonances that complete the heavy-quark spin multiplets. Our model reproduces the \Lambda_b(5912) and \Lambda_b(5920) baryons, which were recently observed by the LHCb collaboration. According to our analysis, these two states are heavy-quark spin symmetric partners. We also make predictions for few \Xi_b baryon resonances, which belong to the same SU(3)xHQSS multiplets as the \Lambda_b particles.

Unitary coupled-channels model for three-mesons decays of heavy mesons

A unitary coupled-channels model is presented for investigating the decays of heavy mesons and excited meson states into three light pseudoscalar mesons. The model accounts for the three-mesons final state interactions in the decay processes, as required by both the three-body and two-body unitarity conditions. In the absence of the Z-diagram mechanisms that are necessary consequences of the three-body unitarity, our decay amplitudes are reduced to a form similar to those used in the so-called isobar-model analysis. We apply our coupled-channels model to the three-pions decays of a1(1260), pi2(1670), pi2(2100), and D0 mesons, and show that the Z-diagram mechanisms can contribute to the calculated Dalitz plot distributions by as much as 30% in magnitudes in the regions where f0(600), rho(770), and f2(1270) dominate the distributions. Also, by fitting to the same Dalitz plot distributions, we demonstrate that the decay amplitudes obtained with the unitary model and the isobar model can be rather different, particularly in the phase that plays a crucial role in extracting the CKM CP-violating phase from the data of B meson decays. Our results indicate that the commonly used isobar model analysis must be extended to account for the final state interactions required by the three-body unitarity to reanalyze the three-mesons decays of heavy mesons, thereby exploring hybrid or exotic mesons, and signatures of physics beyond the standard model.

The reaction π+p → K+∑+ in a unitary coupled-channels model

Elastic πN scattering and the reaction π+p → K+∑+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u-channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

The reaction [formula omitted] in a unitary coupled-channels model

Elastic πN scattering and the reaction π+p→K+Σ+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u-channel exchanges that drive the meson–baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

Publisher’s Note:πN→ωNin a coupled-channel approach [Phys. Rev. C65, 055202 (2002)

We describe the pi N -> omega N cross section from threshold to a center of mass energy of 2 GeV in a unitary coupled-channel model and analyze it in terms of rescattering and resonance excitations. The amplitude is mainly composed of D13, P13, and P11 contributions, where the D13 dominates over the complete considered energy range. We also outline the generalization of the standard partial-wave formalism necessary for the decomposition of the omega N final state.

πN→ωNin a coupled-channel approach

We describe the $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\omega}N$ cross section from threshold to a center-of-mass energy of 2 GeV in a unitary coupled-channel model and analyze it in terms of rescattering and resonance excitations. The amplitude is mainly composed of ${D}_{13},$ ${P}_{13},$ and ${P}_{11}$ contributions, where the ${D}_{13}$ dominates over the complete considered energy range. We also outline the generalization of the standard partial-wave formalism necessary for the decomposition of the $\ensuremath{\omega}N$ final state.

Antiproton-hydrogen annihilation at subkelvin temperatures

The main properties of the interaction of ultra low-energy antiprotons ($% E\le10^{-6}$ a.u.) with atomic hydrogen are established. They include the elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The inverse Auger process ($Pn+e \to H+\bar{p}$) is taken into account in the framework of an unitary coupled-channels model. The annihilation cross-section is found to be several times smaller than the predictions made by the black sphere absorption models. A family of $\bar{p}H$ nearthreshold metastable states is predicited. The dependence of Protonium formation probability on the position of such nearthreshold S-matrix singularities is analysed. An estimation for the $H\bar{H}$ annihilation cross section is obtained.

NEARTHRESHOLD PHENOMENA IN LOW ENERGY ANTIPROTON PHYSICS

The experimental data on low energy [Formula: see text] elastic scattering and annihilation, and on the [Formula: see text] reaction near threshold are well-described in the framework of a simple unitary coupled channel model. Large P-wave enhancement observed in these experiments is shown to be a result of the existence of the nearthreshold bound and resonant P-states of quasinuclear nature in baryon-antibaryon systems. Other possible manifestations of such [Formula: see text] states in the experiments with low energy antiprotons are considered.