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The dynamical mechanism of channel coupling with the decay channels is applied to the case of coupled charmonium--DD* states with JPC=1++. A pole analysis is done and the DD* production cross section is calculated in qualitative agreement with experiment. The sharp peak at the D0D0* threshold and flat background are shown to be due to Breit-Wigner resonance, shifted by channel coupling from the original position of 3954 MeV for the 23P1, QQ state. A similar analysis, applied to the n=2, 3P2, 1P1, 3P0, allows us to associate the first one with the observed Z(3930) J=2 and explains the destiny of 3P0.

We evaluate the light-quark meson contributions to three exact light-by-light scattering sum rules in light of new data by the Belle Collaboration, which recently has extracted the transition form factors of the tensor meson $f_2(1270)$ as well as of the scalar meson $f_0(980)$. We confirm a previous finding that the $\eta, \eta^\prime$ and helicity-2 $f_2(1270)$ contributions saturate one of these sum rules up to photon virtualities around 1 GeV$^2$. At larger virtualities, our sum rule analysis shows an important contribution of the $f_2(1565)$ meson and provides a first empirical extraction of its helicity-2 transition form factor. Two further sum rules allow us to predict the helicity-0 and helicity-1 transition form factors of the $f_2(1270)$ meson. Furthermore, our analysis also provides an update for the scalar and tensor meson hadronic light-by-light contributions to the muon's anomalous magnetic moment.Comment: 21 pages, 4 figure

We present a theoretical study of the γγ * → π + π − , π 0 π 0 processes from the threshold through the f 2 (1270) region in the ππ invariant mass. We adopt the Omnès representation in order to account for rescattering effects in both s-and d-partial waves. For the description of the f 0 (980) resonance, we implement a coupled-channel unitarity. The constructed amplitudes serve as an essential framework to interpret the current experimental two-photon fusion program at BESIII. They also provide an important input for the dispersive analyses of the hadronic light-by-light scattering contribution to the muon's anomalous magnetic moment.

The mechanism of channel coupling via decay products is used to study energy shifts, level mixing as well as the possibility of new near-threshold resonances in cc, bb systems. The Weinberg eigenvalue method is formulated in the multichannel problems, which allows to describe coupledchannel resonances and wave functions in a unitary way, and to predict new states due to channel coupling. Realistic wave functions for all single-channel states and decay matrix elements computed earlier are exploited, and no new fitting parameters are involved. Examples of level shifts, widths and mixings are presented; the dynamical origin of X(3872) and the destiny of the single-channel 2 3 P1(cc) state are clarified. As a result a sharp and narrow peak in the state with quantum numbers J P C = 1 ++ is found at 3.872 GeV, while the single-channel resonance originally around 3.940 GeV, becomes increasingly broad and disappears with growing coupling to open channels.

The di-electron widths of ψ(4040), ψ(4160), and ψ(4415), and their ratios are shown to be in good agreement with experiment, if in all cases the S − D mixing with a large mixing angle θ ≈ 34 • is taken. Arguments are presented why continuum states give small contributions to the wave functions at the origin. We find that the Y (4360) resonance, considered as a pure 3 3 D 1 state, would have very small di-electron width, Γ ee (Y (4360)) = 0.060 keV. On the contrary, for large mixing between the 4 3 S 1 and 3 3 D 1 states with the mixing angle θ = 34.8 • , Γ ee (ψ(4415)) = 0.57 keV coincides with the experimental number, while a second physical resonance, probably Y (4360), has also a rather large Γ ee (Y (∼ 4400)) = 0.61 keV. For the higher resonance Y (4660), considered as a pure 5 3 S 1 state, we predict the di-electron width Γ ee (Y (4660)) = 0.70 keV, but it becomes significantly smaller, namely 0.31 keV, if the mixing angle between the 5 3 S 1 and 4 3 D 1 states θ = 34 • . The mass and di-electron width of the 6 3 S 1 charmonium state are calculated.

We present a unitary multichannel model forKN scattering in the resonance region that fulfills unitarity. It has the correct analytical properties for the amplitudes once they are extended to the complex-s plane and the partial waves have the right threshold behavior. To determine the parameters of the model, we have fitted single-energy partial waves up to J = 7/2 and up to 2.15 GeV of energy in the center-of-mass reference frame obtaining the poles of the Λ * and Σ * resonances, which are compared to previous analyses. We provide the most comprehensive picture of the S = −1 hyperon spectrum to date. Important differences are found between the available analyses making the gathering of further experimental information onKN scattering mandatory to make progress in the assessment of the hyperon spectrum.