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Ikeno, N., Molina, R., & Oset, E. (2021). Triangle singularity mechanism for the pp -> pi(+)d fusion reaction. Phys. Rev. C, 104(1), 014614–16pp.
Abstract: We develop a model for the pp -> pi(+)d reaction based on the pp -> Delta(1232)N transition followed by Delta(1232) -> pi N' decay and posterior fusion of NN' to give the deuteron. We show that the triangle diagram depicting this process develops a triangle singularity leading to a large cross section of this reaction compared to ordinary fusion reactions. The results of the calculation also show that the process is largely dominated by the pp system in L = 2 and S = 0, which transfers J = 2 to the final pi(+)d system. This feature is shown to be well suited to provide L = 2, S = 1, and J(tot) = 3 for np in the np(I = 0) pi(-)pp reaction followed by the pp -> pi(+)d reaction, which has been proposed recently, as a means of describing the so far assumed dibaryon d* (2380) peak.
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Dias, J. M., Toledo, G., Roca, L., & Oset, E. (2021). Unveiling the K-1(1270) double-pole structure in the (B)over-bar -> J/psi rho(K)over-bar and (B)over-bar -> J/psi(K)over-bar*pi decays. Phys. Rev. D, 103(11), 116019–13pp.
Abstract: By looking at the pseudoscalar-vector meson spectra in the (B) over bar -> J/psi rho(K) over bar and (B) over bar -> J/psi(K) over bar*pi weak decays, we theoretically investigate the double-pole structure of the K-1 (1270) resonance by using the chiral unitary approach to account for the final-state interactions between the pseudoscalar (P) and vector (V) mesons. The K-1 (1270) resonance is dynamically generated through these interactions in coupled channels and influences the shape of the invariant mass distributions under consideration. We show how these shapes are affected by the K-1 (1270) double-pole structure to confront the results from our model with future experiments that might investigate the PV spectra in these decays.
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Toledo, G., Ikeno, N., & Oset, E. (2021). Theoretical study of the D-0 -> K-pi(+)eta reaction. Eur. Phys. J. C, 81(3), 268–11pp.
Abstract: We develop a model to study the D-0 -> K-pi(+)eta weak decay, starting with the color favored external emission and Cabibbo favored mode at the quark level. A less favored internal emission decay mode is also studied as a source of small corrections. Some pairs of quarks are allowed to hadronize producing two pseudoscalar mesons, which posteriorly are allowed to interact to finally provide the K-pi(+)eta state. The chiral unitary approach is used to take into account the final state interaction of pairs of mesons, which has as a consequence the production of the kappa (K-0*(700)) and the a(0)(980) resonances, well visible in the invariant mass distributions. We also introduce the (K) over bar*(0)eta production in a phenomenological way and show that the s-wave pseudoscalar interaction together with this vector excitation mode are sufficient to provide a fair reproduction of the experimental data. The model provides the relative weight of the a(0)(980) to the kappa excitation, and their strength is clearly visible in the low energy part of the K pi spectrum.
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Wang, E., Li, H. S., Liang, W. H., & Oset, E. (2021). Analysis of the gamma gamma -> D(D)over-bar reaction and the D(D)over-bar bound state. Phys. Rev. D, 103(5), 054008–10pp.
Abstract: In this work, we investigate the reaction of gamma gamma -> D (D) over bar, taking into account the S-wave D (D) over bar final state interaction. By fitting to the D (D) over bar, invariant mass distributions measured by the Belle and BABAR Collaborations, we obtain a good reproduction of the data by means of a D (D) over bar, amplitude that produces a bound D (D) over bar, statewith isospin I = 0 close to threshold. The error bands of the fits indicate, however, that more precise data on this reaction are needed to be more assertive about the position and width of such a state.
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Ikeno, N., Molina, R., & Oset, E. (2021). The Z(cs)(3985) as a threshold effect from the (D)over-bar(s)*D + (D)over-bar(s)D* interaction. Phys. Lett. B, 814, 136120–5pp.
Abstract: We study the e(+)e(-) -> K+(D-s*D--(0) + Ds-D*(0)) reaction recently measured at BESIII, from where a new Z(cs) state has been reported. We study the interaction of (D) over bar D-s* with the coupled channels J/psi K-, K*(-)eta(c), Ds-D*(0), D-s*D--(0) by means of an extension to the charm sector of the local hidden gauge approach. We find that the Ds-D*(0) + D-s*D--(0) combination couples to J/psi K- and K*(-)eta(c), but the Ds-D*(0 ) -D-s*D--(0) combination does not. The coupled channels help to build up strength in the Ds-D*(0) + D-s*D--(0) diagonal scattering matrix close to threshold and, although the interaction is not strong enough to produce a bound state or resonance, it is sufficient to produce a large accumulation of strength at the (D) over bar D-s* threshold in the e(+)e(-) -> K+(D-s*D--(0) + Ds-D*(0)) reaction in agreement with experiment.
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Roca, L., & Oset, E. (2021). Scalar resonances in the D+ -> K-K+K+ decay. Phys. Rev. D, 103(3), 034020–9pp.
Abstract: We study theoretically the resonant structure of the double Cabibbo suppressed D+ -> K-K+K+ decay. We start from an elementary production diagram, considered subleading in previous approaches, which cannot produce a final K-K+ pair at the tree level but which we show to be able to provide the strength of the decay through final meson-meson state interaction. The different meson-meson elementary productions are related through SU(3), and the final rescattering is implemented from a suitable implementation of unitary extensions of chiral perturbation theory, which generate dynamically the scalar resonances1 f(0)(980) and a(0)(980). We obtain a good agreement with recent experimental data from the LHCb Collaboration with a minimal freedom in the fit and show the dominance of the a(0)(980) contribution close to the threshold of the K-K+ spectrum.
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Wang, E., Liang, W. H., & Oset, E. (2021). Analysis of the e(+)e(-) -> J/psi D(D)over-bar reaction close to the threshold concerning claims of a chi(c0)(2P) state. Eur. Phys. J. A, 57(1), 38–9pp.
Abstract: We analyze the D (D) over bar mass distribution from a recent Belle experiment on the e(+)e(-) -> J/.D (D) over bar reaction, and show that the mass distribution divided by phase sp(c)e does not have a clear peak above the D (D) over bar threshold that justifies the experimental claim of chi(c0)(2P) state from those data. Then we use a unitary formalismwith coupled channels D+ D-, D-0 (D) over bar (0), D-s(D) over bar (s), and eta eta, with some of the interactions taken from a theoretical model, and use the data to fix other parameters. We then show that, given the poor quality of the data, we can get different fits leading to very different D (D) over bar amplitudes, some of them supporting a D (D) over bar bound state and others not. The main conclusion is that the claim for the chi(c0)(2P) state, already included in the PDG, is premature, but refined data can provide very valuable information on the D (D) over bar scattering amplitude. As side effects, we warn about the use of a Breit-Wigner amplitude parameterization close to threshold, and show that the D-s(D) over bar (s) channel plays an important role in this reaction.
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Molina, R., & Oset, E. (2020). Molecular picture for the X-0(2866) as a D*(K)over-bar* J(P)=0(+) state and related 1(+), 2(+) states. Phys. Lett. B, 811, 135870–7pp.
Abstract: We recall the predictions made ten years ago about a bound state of J(P) = 0(+) in I = 0 of the D*(K) over bar* system, which is manifestly exotic, and we associate it to the X-0(2866) state reported in the recent LHCb experiment. Fine tuning the parameters to reproduce exactly the mass and width of the X-0(2866) state, we report two more states stemming from the same interaction, one with 1(+) and the other with 2(+). For reasons of parity, the 1(+) state cannot be observed in D (K) over bar decay, and we suggest to observe it in the D*(K) over bar spectrum. On the other hand, the 2(+) state can be observed in D (K) over bar decay but the present experiment has too small statistics in the region of its mass to make any claim. We note that measurements of the D*(K) over bar spectrum and of the D (K) over bar with more statistics should bring important information concerning the nature of the X-0(2866) and related ones that could be observed.
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Martinez Torres, A., Khemchandani, K. P., Roca, L., & Oset, E. (2020). Few-body systems consisting of mesons. Few-Body Syst., 61(4), 35–16pp.
Abstract: We present a work which is meant to inspire the few-body practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on two-body problems, to move in the direction of studying related few-body systems. For this purpose we devote the discussions in the introduction to show how the input two-body amplitudes can be easily obtained using techniques of the chiral unitary theory, or its extensions to the heavy quark sector. We then briefly explain how these amplitudes can be used to solve the Faddeev equations or a simpler version obtained by treating the three-body scattering as that of a particle on a fixed center. Further, we give some examples of the results obtained by studying systems involving mesons. We have also addressed the field of many meson systems, which is currently almost unexplored, but for which we envisage a bright future. Finally, we give a complete list of works dealing with unconventional few-body systems involving one or several mesons, summarizing in this way the findings on the topic, and providing a motivation for those willing to investigate such systems.
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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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