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Yu, Q. X., Pavao, R., Debastiani, V. R., & Oset, E. (2019). Description of the Xic and Xib states as molecular states. Eur. Phys. J. C, 79(2), 167–14pp.
Abstract: In this work we study several c and b states dynamically generated from the meson-baryon interaction in coupled channels, using an extension of the local hidden gauge approach in the Bethe-Salpeter equation. These molecular states appear as poles of the scattering amplitudes, and several of them can be identified with the experimentally observed c states, including the c(2790), c(2930), c(2970), c(3055) and c(3080). Also, for the recently reported b(6227) state, we find two poles with masses and widths remarkably close to the experimental data, for both the JP=1/2- and JP=3/2- sectors.
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Liang, W. H., Dias, J. M., Debastiani, V. R., & Oset, E. (2018). Molecular Omega(b) states. Nucl. Phys. B, 930, 524–532.
Abstract: Motivated by the recent finding of five Omega(c) states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson-baryon with the quantum numbers of Omega(c), we extend these ideas and make predictions for the interaction of meson-baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several Omega(b) states: two states with masses 6405 MeV and 6465 MeV for J(P) = 1/2(-) ; two more states with masses 6427 MeV and 6665 MeV for 3/4(-) ; and three states between 6500 and 6820 MeV, degenerate with J(P) = 1/2(-), 3/4(-), stemming from the interaction of vector-baryon in the beauty sector.
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Dias, J. M., Debastiani, V. R., Xie, J. J., & Oset, E. (2018). The radiative decay D-0 -> (K)over-bar*(0)gamma with vector meson dominance. Chin. Phys. C, 42(4), 043106–7pp.
Abstract: Motivated by the experimental measurements of D-0 radiative decay modes, we have proposed a model to study the D-0 -> (K) over bar*(0)gamma decay, by establishing a link with D-0 -> (K) over bar*(0) V (V = rho(0), omega) decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for V gamma conversion. As a result, we have found the branching ratio B[D-0 -> (K) over bar*(0)gamma]=(1.55-3.44)x10(-4), which is in fair agreement with the experimental values reported by the Belle and BaBar collaborations.
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Dias, J. M., Debastiani, V. R., Xie, J. J., & Oset, E. (2018). Doubly charmed Xi(cc) molecular states from meson-baryon interaction. Phys. Rev. D, 98(9), 094017–11pp.
Abstract: Stimulated by the new experimental LHCb findings associated with the Omega(c) states, some of which we have described in a previous work as being dynamically generated through meson-baryon interaction, we have extended this approach to make predictions for new Xi(cc) molecular states in the C = 2, S = 0, and I = 1/2 sector. These states manifest themselves as poles in the solution of the Bethe-Salpeter equation in coupled channels. The kernels of this equation were obtained using general Lagrangians coming from the hidden local gauge symmetry or massive Yang-Mills theory, and the interactions are dominated by the exchange of light vector mesons. The extension of this approach to the heavy sector stems from the realization that the dominant interaction corresponds to having the heavy quarks as spectators, which implies the preservation of the heavy quark symmetry. As a result, we get several states: three states from the pseudoscalar meson-baryon interaction with J(P) = 1/2(-), and masses around 3840, 4080 and 4090 MeV, and two at 3920 and 4150 MeV for J(P) = 3/2(-). Furthermore, from the vector meson-baryon interaction we get three states degenerate with J(P) 1/2(-) and 3/2(-) from 4220 MeV to 4290 MeV, and two more states around 4280 and 4370 MeV, degenerate with J(P) = 1/2(-), 3/2(-), and 5/2(-).
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Dias, J. M., Debastiani, V. R., Roca, L., Sakai, S., & Oset, E. (2017). Binding of the BD(D)over-bar and BDD systems. Phys. Rev. D, 96(9), 094007–6pp.
Abstract: We study theoretically the BD (D) over bar and BDD systems to see if they allow for possible bound or resonant states. The three-body interaction is evaluated implementing the fixed center approximation to the Faddeev equations which considers the interaction of a D or (D) over bar particle with the components of a BD cluster, previously proved to form a bound state. We find an I(J(P)) = 1/2(0(-)) bound state for the BD (D) over bar system at an energy around 8925-8985 MeV within uncertainties, which would correspond to a bottom hidden-charm meson. In contrast, for the BDD system, which would be bottom double-charm and hence manifestly exotic, we have found hints of a bound state in the energy region 8935-8985 MeV, but the results are not stable under the uncertainties of the model, and we cannot assure, nor rule out, the possibility of a BDD three-body state.
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Debastiani, V. R., Sakai, S., & Oset, E. (2017). Role of a triangle singularity in the pi N(1535) contribution to gamma p -> p pi(0) eta. Phys. Rev. C, 96(2), 025201–7pp.
Abstract: We have studied the gamma p -> p pi(0) eta reaction paying attention to the two main mechanisms at low energies, the gamma p ->Delta(1700) -> eta Delta(1232) and the gamma p -> Delta(1700) -> pi N(1535). Both are driven by the photoexcitation of the Delta (1700) and the second one involves a mechanism that leads to a triangle singularity. We are able to evaluate quantitatively the cross section for this process and show that it agrees with the experimental determination. Yet there are some differences with the standard partial wave analysis which does not include explicitly the triangle singularity. The exercise also shows the convenience of exploring possible triangle singularities in other reactions and how a standard partial wave analysis can be extended to accommodate them.
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Debastiani, V. R., Sakai, S., & Oset, E. (2019). Considerations on the Schmid theorem for triangle singularities. Eur. Phys. J. C, 79(1), 69–13pp.
Abstract: We investigate the Schmid theorem, which states that if one has a tree level mechanism with a particle decaying to two particles and one of them decaying posteriorly to two other particles, the possible triangle singularity developed by the mechanism of elastic rescattering of two of the three decay particles does not change the cross section provided by the tree level. We investigate the process in terms of the width of the unstable particle produced in the first decay and determine the limits of validity and violation of the theorem. One of the conclusions is that the theorem holds in the strict limit of zero width of that resonance, in which case the strength of the triangle diagram becomes negligible compared to the tree level. Another conclusion, on the practical side, is that for realistic values of the width, the triangle singularity can provide a strength comparable or even bigger than the tree level, which indicates that invoking the Schmid theorem to neglect the triangle diagram stemming from elastic rescattering of the tree level should not be done. Even then, we observe that the realistic case keeps some memory of the Schmid theorem, which is visible in a peculiar interference pattern with the tree level.
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Debastiani, V. R., & Navarra, F. S. (2019). A non-relativistic model for the [cc][(c)over-bar(c)over-bar] tetraquark. Chin. Phys. C, 43(1), 013105–20pp.
Abstract: We use a non-relativistic model to study the spectroscopy of a tetraquark composed of [cc][(c) over bar(c) over bar] in a diquark-antidiquark configuration. By numerically solving the Schrodinger equation with a Cornell-inspired potential, we separate the four-body problem into three two-body problems. Spin-dependent terms (spin-spin, spin-orbit and tensor) are used to describe the splitting structure of the c (c) over bar spectrum and are also extended to the interaction between diquarks. Recent experimental data on charmonium states are used to fix the parameters of the model and a satisfactory description of the spectrum is obtained. We find that the spin-dependent interaction is sizable in the diquark-antidiquark system, despite the heavy diquark mass, and also that the diquark has a finite size if treated in the same way as the c (c) over bar systems. We find that the lowest S-wave T-4c tetraquarks might be below their thresholds of spontaneous dissociation into low-lying charmonium pairs, while orbital and radial excitations would be mostly above the corresponding charmonium pair thresholds. Finally, we repeat the calculations without the confining part of the potential and obtain bound diquarks and bound tetraquarks. This might be relevant to the study of exotic charmonium in the quark-gluon plasma. The T4c states could be investigated in the forthcoming experiments at the LHC and Belle II.
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Debastiani, V. R., Liang, W. H., Xie, J. J., & Oset, E. (2017). Predictions for eta(c) -> eta pi(+)pi(-) producing f(0)(500), f(0)(980) and a(0)(980). Phys. Lett. B, 766, 59–64.
Abstract: We perform calculations for the eta(c) -> eta pi(+)pi(-) decay using elements of SU(3) symmetry to see the weight of different trios of pseudoscalars produced in this decay, prior to the final state interaction of the mesons. After that, the interaction of pairs of mesons, leading finally to eta pi(+)pi(-), is done using the chiral unitary approach. We evaluate the pi(+)pi(-) and pi eta mass distributions and find large and clear signals for f(0)(500), f(0)(980) and a(0)(980) excitation. The reaction is similar to the chi(c1) -> eta pi(+)pi(-), which has been recently measured at BESIII and its implementation and comparison with these predictions will be very valuable to shed light on the nature of the low mass scalar mesons.
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Debastiani, V. R., Dias, J. M., & Oset, E. (2017). Study of the DKK and DK(K)over-bar systems. Phys. Rev. D, 96(1), 016014–9pp.
Abstract: Using the fixed center approximation to Faddeev equations, we investigate the DKK and DK (K) over bar three-body systems, considering that the DK dynamically generates, through its I = 0 component, the D(so)(*()2317) molecule. According to our findings, for the DK (K) over bar interaction we find evidence of a state I(J(p)) = 1/2 (0(-)) just above the D-s0(*)(2317) (K) over bar threshold and around the Df(0)(980) threshold, with mass of about 2833-2858 MeV, made mostly of Df(0)(980). On the other hand, no evidence related to a state from the DKK interaction is found. The state found could be seen in the ppD invariant mass.
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