
Abreu, L. M., Albaladejo, M., Feijoo, A., Oset, E., & Nieves, J. (2023). Shedding light on the X(3930) and X(3960) states with the B> K J/psi omega reaction. Eur. Phys. J. C, 83(4), 309–11pp.
Abstract: We have studied the contribution of the state X(3930), coming from the interaction of the D ($) over bar and Ds(+) D ($) over bar (s) channels, to the B > K J/psi omega decay. The purpose of this work is to offer a complementary tool to see if the X(3930) state observed in the D+ D channel is the same or not as the X(3960) resonance claimed by the LHCb Collaboration from a peak in the Ds(+) D s mass distribution around threshold. We present results for what we expect in the J/psi omega mass distribution in the B > K J/psi omega decay and conclude that a clear signal should be seen around 3930 MeV. At the same time, finding no extra resonance signal at 3960 MeV would be a clear indication that there is not a new state at 3960 MeV, supporting the hypothesis that the nearthreshold peaking structure peak in the Ds(+) Ds() mass distribution is only a manifestation of a resonance below threshold.



Bayar, M., Feijoo, A., & Oset, E. (2023). X(3960) seen in Ds plus Ds as the X(3930) state seen in D plus D. Phys. Rev. D, 107(3), 034007–5pp.
Abstract: We perform a calculation of the interaction of the D over bar D, Ds over bar Ds coupled channels and find two bound states, one coupling to DD over bar and another one at higher energies coupling mostly to D+s Ds . We identify this latter state with the X0(3930) seen in the D+D mass distribution in the B+ D+DK+ decay, and also show that it produces an enhancement of the D+s Ds mass distribution close to threshold which is compatible with the recent LHCb observation in the B+ D+s Ds K+ decay which has been identified as a new state, X0(3960).



Dai, L. R., Abreu, L. M., Feijoo, A., & Oset, E. (2023). The isospin and compositeness of the Tcc(3875) state. Eur. Phys. J. C, 83(10), 983–11pp.
Abstract: We perform a fit to the LHCb data on the Tcc(3875) state in order to determine its nature. We use a general framework that allows to have the (DD & lowast;+)D0, (D+D & lowast;0) components forming a molecular state, as well as a possible nonmolecular state or contributions from missing coupled channels. From the fits to the data we conclude that the state observed is clearly of molecular nature from the (DD & lowast;+)D0, (D+D & lowast;0) components and the possible contribution of a nonmolecular state or missing channels is smaller than 3%, compatible with zero. We also determine that the state has isospin I=0 with a minor isospin breaking from the different masses of the channels involved, and the probabilities of the (DD & lowast;+)D0, (D+D & lowast;0) channels are of the order of 69% and 29% with uncertainties of 1%. The differences between these probabilities should not be interpreted as a measure of the isospin violation. Due to the short range of the strong interaction where the isospin is manifested, the isospin nature is provided by the couplings of the state found to the (DD & lowast;+)D0, (D+D & lowast;0) components, and our results for these couplings indicate that we have an I=0 state with a very small isospin breaking. We also find that the potential obtained provides a repulsive interaction in I=1, preventing the formation of an I=1 state, in agreement with what is observed in the experiment.



Dai, L. R., Oset, E., Feijoo, A., Molina, R., Roca, L., Martinez Torres, A., et al. (2022). Masses and widths of the exotic molecular B(s)(()*B)((s))(*()) states. Phys. Rev. D, 105(7), 074017–11pp.
Abstract: We study the interaction of the doubly bottom systems BB, B*B, BsB, Bs*B, B*B*, B*BS, B*Bs*, BsBs, BsBs*, Bs*Bs* by means of vector meson exchange with Lagrangians from an extension of the local hidden gauge approach. The full swave scattering matrix is obtained implementing unitarity in coupled channels by means of the BetheSalpeter equation. We find poles below the channel thresholds for the attractively interacting channels B*B in I = 0, Bs*B – B*Bs in I = 1/2, B* B* in I = 0, and Bs*B* in I = 1/2, all of them with J(P) = 1(+). For these cases the widths are evaluated identifying the dominant source of imaginary part. We find binding energies of the order of 1020 MeV, and the widths vary much from one system to the other: of the order of 10100 eV for the B* B system and Bs*B – B* Bs, about 6 MeV for the B*B* system and of the order of 0.5 MeV for the Bs*B* system.



Feijoo, A., Dai, L. R., Abreu, L. M., & Oset, E. (2024). Correlation function for the Tbb state: Determination of the binding, scattering lengths, effective ranges, and molecular probabilities. Phys. Rev. D, 109(1), 016014–8pp.
Abstract: We perform a study of the (B*+B0), (BB+)B*0 correlation functions using an extension of the local hidden gauge approach which provides the interaction from the exchange of light vector mesons and gives rise to a bound state of these components in I = 0 with a binding energy of about 21 MeV. After that, we face the inverse problem of determining the low energy observables, scattering length and effective range for each channel, the possible existence of a bound state, and, if found, the couplings of such a state to each (B*+B0), (BB+)B*0 component as well as the molecular probabilities of each of the channels. We use the bootstrap method to determine these magnitudes and find that, with errors in the correlation function typical of present experiments, we can determine all these magnitudes with acceptable precision. In addition, the size of the source function of the experiment from where the correlation functions are measured can be also determined with a high precision.



Feijoo, A., Gazda, D., Magas, V., & Ramos, A. (2021). The (K)overbarN Interaction in Higher Partial Waves. SymmetryBasel, 13(8), 1434–22pp.
Abstract: We present a chiral (K) over barN interaction model that has been developed and optimized in order to account for the experimental data of inelastic (K) over barN reaction channels that open at higher energies. In particular, we study the effect of the higher partial waves, which originate directly from the chiral Lagrangian, as they could supersede the role of highspin resonances employed in earlier phenomenological models to describe mesonbaryon cross sections in the 2 GeV region. We present a detailed derivation of the partial wave amplitudes that emerge from the chiral SU(3) mesonbaryon Lagrangian up to the dwaves and nexttoleading order in the chiral expansion. We implement a nonperturbative unitarization in coupled channels and optimize the model parameters to a large pool of experimental data in the relevant energy range where these new contributions are expected to be important. The obtained results are encouraging. They indicate the ability of the chiral higher partial waves to extend the description of the scattering data to higher energies and to account for structures in the reaction crosssections that cannot be accommodated by theoretical models limited to the swaves.



Feijoo, A., Liang, W. H., & Oset, E. (2021). (DD0)D0 pi(+) mass distribution in the production of the Tcc exotic state. Phys. Rev. D, 104(11), 114015–7pp.
Abstract: We perform a unitary coupled channel study of the interaction of the D*D+(0), D*D0(+) channels and find a state barely bound, very close to isospin I = 0. We take the experimental mass as input and obtain the width of the state and the (DD0 pi)D0+ mass distribution. When the mass of the Tcc state quoted in the experimental paper from raw data is used, the width obtained is of the order of the 80 keV, small compared to the value given in that work. Yet, when the mass obtained in an analysis of the data considering the experimental resolution is taken, the width obtained is about 43 keV and both the width and the (DD0 pi+)D0 mass distribution are in remarkable agreement with the results obtained in that latter analysis.



Feijoo, A., Magas, V. K., Ramos, A., & Oset, E. (2016). A hiddencharm S =1 pentaquark from the decay Lambda(b) into J/psi eta Lambda states. Eur. Phys. J. C, 76(8), 446–12pp.
Abstract: The hiddencharm pentaquark Pc(4450) observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness S = 1 sector. In this work we argue that a hiddencharm strange pentaquark could be seen from the decay of the Lambda b, just as in the case of the nonstrange Pc(4450), but looking into the J/psi eta Lambda decay mode and forming the invariant mass spectrum of J/psi Lambda pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and finalstate interaction effects, we find the J/psi eta Lambda final states to be populated with similar strength as the J/psi K p states employed for the observation of the nonstrange pentaquark. This makes the Lambda b > J/psi eta Lambda decay to be an interesting process to observe a possible strange partner of the Pc(4450). We study the dependence of the J/psi Lambda mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.



Feijoo, A., Magas, V. K., Ramos, A., & Oset, E. (2015). Lambda(b) > J/psi K Xi decay and the higher order chiral terms of the meson baryon interaction. Phys. Rev. D, 92(7), 076015–10pp.
Abstract: We study the weak decay of the Lambda(b) into J/psi K Xi. and J/psi eta Lambda states, and relate these processes to the Lambda(b) > J/psi(K) over barN decay mode. The elementary weak transition at the quark level proceeds via the creation of a J/psi meson and an excited sud system with I = 0, which upon hadronization leads to (K) over barN or eta Lambda pairs. These states undergo finalstate interaction in coupled channels and produce a final mesonbaryon pair. The K. state only occurs via rescattering, hence making the Lambda(b) > J/psi K Xi process very sensitive to the details of the mesonbaryon interaction in strangeness S = 1 and isospin I = 0. We show that the corresponding invariant mass distribution is dominated by the nexttoleadingorder terms of the chiral interaction. The I = 0 selectivity of this decay, and its large sensitivity to the higherorder terms, makes its measurement very useful and complementary to the K p > K Xi cross section data. The rates of the Lambda(b) > J/psi K Xi and Lambda(b) > J/psi eta Lambda invariant mass distributions are sizable compared to those of the Lambda(b) > J/psi(K) over barN decay, which is measured experimentally, and thus, we provide arguments for an experimental determination of these decay modes that will help us understand better the chiral dynamics at higher energies.



Feijoo, A., Molina, R., Dai, L. R., & Oset, E. (2022). Lambda(1405) mediated triangle singularity in the K()d > p Sigma() reaction. Eur. Phys. J. C, 82(11), 1028–16pp.
Abstract: We study for the first time the p Sigma() > K d and K d > p Sigma() reactions close to threshold and show that they are driven by a triangle mechanism, with the Lambda(1405), a proton and a neutron as intermediate states, which develops a triangle singularity close to the (K) over bard threshold. We find that a mechanism involving virtual pion exchange and the K p > pi(+)Sigma() amplitude dominates over another one involving kaon exchange and the K p > K p amplitude. Moreover, of the two Lambda(1405) states, the one with higher mass around 1420 MeV, gives the largest contribution to the process. We show that the cross section, well within measurable range, is very sensitive to different models that, while reproducing (K) over barN observables above threshold, provide different extrapolations of the (K) over barN amplitudes below threshold. The observables of this reaction will provide new constraints on the theoretical models, leading to more reliable extrapolations of the (K) over barN amplitudes below threshold and to more accurate predictions of the Lambda(1405) state of lower mass.

