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Dai, L. R., Dias, J. M., & Oset, E. (2018). Disclosing D* (D)over bar* molecular states in the B-c(-) -> pi(-) J/psi omega decay. Eur. Phys. J. C, 78(3), 210–7pp.
Abstract: We study the B-c(-) -> pi(-) J/omega and B-c(-) -> pi(-) D* (D) over bar* reactions and show that they are related by the presence of two resonances, the X(3940) and X(3930), that are of molecular nature and couple most strongly to D* (D) over bar*, but also to J/psi omega. Because of that, in the J/psi omega mass distribution we find a cusp with large strength at the D* (D) over bar* threshold and predict the ratio of strengths between the peak of the cusp and the maximum of the D* (D) over bar* distribution close to D* (D) over bar* threshold, which are distinct features of the molecular nature of these two resonances.
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Dai, L. R., & Oset, E. (2018). Helicity amplitudes in B -> D*(nu)over-barl decay. Eur. Phys. J. C, 78(11), 951–11pp.
Abstract: We use a recent formalism of the weak hadronic reactions that maps the transition matrix elements at the quark level into hadronic matrix elements, evaluated with an elaborate angular momentum algebra that allows finally to write the weak matrix elements in terms of easy analytical formulas. In particular they appear explicitly for the different spin third components of the vector mesons involved. We extend the formalism to a general case, with the operator parameter, which suggest to use this magnitude to test different models beyond the standard model. We show that our formalism implies the heavy quark limit and compare our results with calculations that include higher order corrections in heavy quark effective theory. We find very similar results for both approaches in normalized distributions, which are practically identical at the end point of M-inv((nu l)) = m(B) – m(D)*
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Dai, L. R., Toledo, G., & Oset, E. (2020). Searching for a D(D)over-bar bound state with the psi(3770) -> gamma D-0(D)over-bar(0) decay. Eur. Phys. J. C, 80(6), 510–8pp.
Abstract: We perform a calculation of the mass distribution in the psi(3770) -> gamma D (D) over bar decay, studying both the D+D- and D-0(D) over bar (0) decays. The electromagnetic interaction is such that the tree level amplitude is null for the neutral channel, which forces the psi(3770) -> gamma D-0(D) over bar (0) transition to go through a loop involving the D+D- -> D-0(D) over bar (0) scattering amplitude. We take the results for this amplitude from a theoretical model that predicts a D (D) over bar bound state and find a D-0(D) over bar (0) mass distribution in the decay drastically different than phase space. The rates obtained are relatively large and the experiment is easily feasible in the present BESIII facility. The performance of this experiment could provide an answer to the issue of this much searched for state, which is the analogue of the f(0)(980) resonance.
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Dai, L. R., Roca, L., & Oset, E. (2020). Tau decay into tau(t) and a(1)(1260), b(1)(1235), and two K-1(1270). Eur. Phys. J. C, 80(7), 673–9pp.
Abstract: We study the tau -> nu(tau). A decay, with A an axialvector meson. We produce the a(1) (1260) and b(1) (1235) resonances in the Cabibbo favored mode and two K-1 (1270) states in the Cabibbo suppressed mode. We take advantage of previous chiral unitary approach results where these resonances appear dynamically from the vector and pseudoscalar meson interaction in s-wave. Actually two different poles were obtained associated to the K-1(1270) quantum numbers. We find that the unmeasured rates for b(1)(1235) production are similar to those of the a(1)(1260) and for the two K-1 states we suggest to separate the present information on the (K) over bar pi pi invariant masses into (K) over bar*pi and rho K modes, the channels to which these two resonances couple most strongly, predicting that thesemodes peak at different energies and have different widths. These measurements should shed light on the existence of these two K-1 states. In addition, we have gone one step further making a comparison with experimental results of three meson decay channels, letting the vector mesons of our approach decay into pseudoscalars, and we find an overall good agreement with experiment.
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Dai, L. R., Oset, E., & Geng, L. S. (2022). The D-s(+)->pi(+KSKS0)-K-0 reaction and the I=1 partner of the f(0)(1710) state. Eur. Phys. J. C, 82(3), 225–9pp.
Abstract: We have identified the decay modes of the D-s(+)-> pi K+*K+*(-),pi+K*(0)(K) over bar*(0) reactions producing a pion and two vector mesons. The posterior vector-vector interaction generates two resonances that we associate to the f(0)(1710) and the a(0)(1710) recently claimed, and they decay to the observed K+K- or (KSKS0)-K-0 pair, leading to the reactions D-s(+)->pi+K+K-,pi(+KSKS0)-K-0. The results depend on two parameters related to external and internal emission. We determine a narrow region of the parameters consistent with the large N-c limit within uncertainties which gives rise to decay widths in agreement with experiment. With this scenario we make predictions for the branching ratio of the a(0)(1710) contribution to the D-s(+)->pi(K+KS0)-K-0 reaction, finding values within the range of (1.3 +/- 0.4)x10(-3). Comparison of these predictions with coming experimental results on that latter reaction will be most useful to deepen our understanding on the nature of these two resonances.
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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.
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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 T-cc(3875) state in order to determine its nature. We use a general framework that allows to have the (DD & lowast;+)-D-0, (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;+)-D-0, (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;+)-D-0, (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;+)-D-0, (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.
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Xie, J. J., Dai, L. R., & Oset, E. (2015). The low lying scalar resonances in the D-0 decays into K-s(0) and f(0)(500), f(0)(980), a(0)(980). Phys. Lett. B, 742, 363–369.
Abstract: The D-0 decay into K-s(0) and a scalar resonance, f(0)(500), f(0)(980), a(0)(980), are studied obtaining the scalar resonances from final state interaction of a pair of mesons produced in a first step in the D-0 decay into K-s(0) and the pair of pseudoscalar mesons. This weak decay is very appropriate for this kind of study because it allows to produce the three resonances in the same decay in a process that is Cabibbo-allowed, hence the rates obtained are large compared to those of (B) over bar (0) decays into J/psi and a scalar meson that have at least one Cabibbo-suppressedvertex. Concretely the a(0)(980) production is Cabibbo-allowedhere, while it cannot be seen in the (B) over bar (0)(s) decay into J/psi a(0)(980) and is doubly Cabibbo-suppressedin the (B) over bar (0) decay into J/psi a(0)(980) and has not been identified there. The fact that the three resonances can be seen in the same reaction, because there is no isospin conservation in the weak decays, offers a unique opportunity to test the ideas of the chiral unitary approach where these resonances are produced from the interaction of pairs of pseudoscalar mesons.
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Dai, L. R., Molina, R., & Oset, E. (2022). The (B)over-bar(0)-> D*+ (D)over-bar*K-0(-) reaction to detect the I=0, J(P)=1+ partner of the X-0(2866). Phys. Lett. B, 832, 137219–5pp.
Abstract: We have chosen the (B) over bar (0)-> D*+ (D) over bar*K-0 reaction in order to observe the I= 0, J(P)= 1(+)(R-1) partner state of the X-0(2866) stemming from the D*+ (K) over bar* molecular picture. The reaction proceeds via external emission in the most favored Cabibbo decay mode and one observes the R(1)state as a very strong peak versus the background in the D*+ K- spectrum. The branching ratio for R1production in this reaction is estimated of the order of 4 x10(-3). The method used, applied to the B+-> D- D+ K+ reaction, produces a ratio of signal to background in the D- K+ spectrum in very good agreement with the LHCb experiment that observed the X-0(2866).
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Abreu, L. M., Dai, L. R., & Oset, E. (2023). J/Psi decay to omega, phi, K*0 plus f0(1370), f0(1710), K0*(1430), f2(1270), f'2 (1525) and K2*(1430): Role of the D-wave for tensor production. Phys. Lett. B, 843, 137999–10pp.
Abstract: We reassess the decay of the J/Psi into an omega, phi, K*0 and one of the f0(1370), f0(1710), f2(1270), f'2 (1525), K0*(1430) and K2*(1430) resonances. We benefit from previous works that considered this reaction as a J/Psi decay into three vector mesons, with a scalar or tensor resonance being formed from the interaction of two of these vectors. The novelty here with respect to former studies is the investigation of the relation between the scalar meson and tensor productions for the first time. To this end, the spin structure of the four vectors present in the production vertex is analyzed, and the D-wave mechanism in the tensor production is included. Then, beyond the ratios studied previously involving scalar states and tensor states independently, new ratios relating the scalar and tensor meson productions are estimated. Our results suggest that the D-wave mechanism of tensor production assumes a relevant contribution. New experimental data reporting the angular distributions of these processes will be important for checking this conclusion.
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