Ikeno, N., Molina, R., & Oset, E. (2022). Zcs states from the D*s over bar D* and J=psi K* coupled channels: Signal in B+ -> J=psi phi K+ decay. Phys. Rev. D, 105(1), 014012–13pp.
Abstract: We study the D*s over bar D* system in connection with the J=psi K* in coupled channels and observe that, within reasonable values of the cutoff used to regularize the loops, the system does not develop a bound state. However, the JP = 2+ channel has enough attraction to create a strong cusp structure that shows up in the J=psi K+ invariant mass distribution in the B+ -> J=psi phi K+ decay at the D*s over bar D* threshold. Such structure is results should stimulate further measurements around this region, given the fact that cusp effects provide as valuable information on hadron dynamics as resonances themselves.
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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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Molina, R., Ikeno, N., & Oset, E. (2023). Sequential single pion production explaining the dibaryon “d*(2380)” peak. Chin. Phys. C, 47(4), 041001–10pp.
Abstract: In this study, we investigate the two step sequential one pion production mechanism, that is, np(I=0)->pi(-)pp followed by the fusion reaction pp ->pi(+)d, to describe the np ->pi(+)pi(-)d reaction with in state I = 0 . In this reaction, a narrow peak identified with a “ d(2380) ” dibaryon has been previously observed. We discover that the second reaction step pp ->pi(+)d is driven by a triangle singularity that determines the position of the peak of the reaction and the high strength of the cross section. The combined cross section of these two mechanisms produces a narrow peak with a position, width, and strength, that are compatible with experimental observations within the applied approximations made. This novel interpretation of the peak accomplished without invoking a dibaryon explains why this peak has remained undetected in other reactions.
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Ikeno, N., Bayar, M., & Oset, E. (2021). Combined theoretical study of the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta reactions. Eur. Phys. J. C, 81(4), 377–10pp.
Abstract: We study the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta reactions, which are single Cabibbo suppressed and can proceed both through internal and external emission. The primary mechanisms at quark level are considered, followed by hadronization to produce three mesons in the D+ decay, and after that the final state interaction of these mesons leads to the production of the a(0)(980) resonance, seen in the pi(+)eta, pi(0)eta mass distributions. The theory has three unknown parameters to determine the shape of the distributions and the ratio between the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta rates. This ratio restricts much the sets of parameters but there is still much freedom leading to different shapes in the mass distributions. We call for a measurement of these mass distributions that will settle the reaction mechanism, while at the same time provide relevant information on the way that the a(0)(980) resonance is produced in the reactions.
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Tani, A., Ikeno, N., Jido, D., Nagahiro, H., Fujioka, H., Itahashi, K., et al. (2021). Structure of double pionic atoms. Prog. Theor. Exp. Phys., 2021(3), 033D02–16pp.
Abstract: We study theoretically the structure of double pionic atoms, in which two negatively charged pions (pi(-)) are bound in the atomic orbits. The double pionic atom is considered to be an interesting system from the point of view of the multi-bosonic systems. In addition, it could be possible to deduce valuable information on the isospin I = 2 pi pi interaction and the pionnucleus strong interaction. In this paper, we take into account the pi pi strong and electromagnetic interactions, and evaluate the effects on the binding energies by perturbation theory for the double pionic atoms in heavy nuclei. We investigate several combinations of two pionic states and find that the order of magnitude of the energy shifts due to the pi pi interaction is around 10 keV for the strong interaction and around 100 keV for the electromagnetic interaction for the ground states.
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