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Albaladejo, M., Guo, F. K., Hidalgo-Duque, C., & Nieves, J. (2016). Z(c)(3900): What has been really seen? Phys. Lett. B, 755, 337–342.
Abstract: The Z(c)(+/-)(3900)/Z(c)(+/-)(3885) resonant structure has been experimentally observed in the Y(4260) -> J/Psi pi pi and Y(4260) -> (D) over bar* D pi decays. This structure is intriguing since it is a prominent candidate of an exotic hadron. Yet, its nature is unclear so far. In this work, we simultaneously describe the (D) over bar* D and J/Psi pi invariant mass distributions in which the Z(c) peak is seen using amplitudes with exact unitarity. Two different scenarios are statistically acceptable, where the origin of the Z(c) state is different. They correspond to using energy dependent or independent (D) over bar *D S-wave interaction. In the first one, the Z(c) peak is due to a resonance with a mass around the D (D) over bar* threshold. In the second one, the Z(c) peak is produced by a virtual state which must have a hadronic molecular nature. In both cases the two observations, Z(c)(+/-)(3900) and Z(c)(+/-)(3885), are shown to have the same common origin, and a (D) over bar *D bound state solution is not allowed. Precise measurements of the line shapes around the D (D) over bar* threshold are called for in order to understand the nature of this state.
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Albaladejo, M., Fernandez-Soler, P., Guo, F. K., & Nieves, J. (2017). Two-pole structure of the D-0*(2400). Phys. Lett. B, 767, 465–469.
Abstract: The so far only known charmed non-strange scalar meson is dubbed as D-0(*)(2400) in the Review of Particle Physics. We show, within the framework of unitarized chiral perturbation theory, that there are in fact two (I = 1/2, J(P) = 0(+)) poles in the region of the D-0(*)( 2400) in the coupled-channel D pi, D eta and D-s (K) over bar scattering amplitudes. With all the parameters previously fixed, we predict the energy levels for the coupled-channel system in a finite volume, and find that they agree remarkably well with recent lattice QCD calculations. This successful description of the lattice data is regarded as a strong evidence for the two-pole structure of the D-0(*)( 2400). With the physical quark masses, the poles are located at (2105(-8)(+6) – i102(-12)(+10)) MeV and (2451(-26)(+36) – i134(-8)(+7)) MeV, with the largest couplings to the D pi and D-s (K) over bar channels, respectively. Since the higher pole is close to the D-s (K) over bar threshold, we expect it to show up as a threshold enhancement in the D-s (K) over bar invariant mass distribution. This could be checked by high-statistic data in future experiments. We also show that the lower pole belongs to the same SU(3) multiplet as the D-s0(*)(2317) state. Predictions for partners in the bottom sector are also given.
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Baru, V., Dong, X. K., Du, M. L., Filin, A., Guo, F. K., Hanhart, C., et al. (2022). Effective range expansion for narrow near-threshold resonances. Phys. Lett. B, 833, 137290–7pp.
Abstract: We discuss some general features of the effective range expansion, the content of its parameters with respect to the nature of the pertinent near-threshold states and the necessary modifications in the presence of coupled channels, isospin violations and unstable constituents. As illustrative examples, we analyse the properties of the chi(c1)(3872) and T-cc(+) states supporting the claim that these exotic states have a predominantly molecular nature.
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Wang, E., Xie, J. J., Liang, W. H., Guo, F. K., & Oset, E. (2017). Role of a triangle singularity in the gamma p -> K+Lambda (1405) reaction. Phys. Rev. C, 95(1), 015205–9pp.
Abstract: We show the effects of a triangle singularity mechanism for the gamma p -> K+Lambda(1405) reaction. The mechanism has a N-* resonance around 2030 MeV, which decays into K*Sigma. The K-* decays to K+ pi, and the pi Sigma merge to form the Lambda (1405). This mechanism produces a peak around root s = 2110 MeV, and has its largest contribution around cos theta= 0. The addition of this mechanism to other conventional ones leads to a good reproduction of d sigma/dcos theta and the integrated cross section around this energy, providing a solution to a problem encountered in previous theoretical models.
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Du, M. L., Baru, V., Dong, X. K., Filin, A., Guo, F. K., Hanhart, C., et al. (2022). Coupled-channel approach to T-cc(+) including three-body effects. Phys. Rev. D, 105(1), 014024–19pp.
Abstract: A coupled-channel approach is applied to the charged tetraquark state T-cc(+). recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body (DD0)-D-0 pi(+) channel. Special attention is paid to the three-body dynamics in the T-cc(+) due to the finite life time of the D*. An approach to the T-cc(+) is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the D and D* mesons and the finite D* width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The (DD0)-D-0 and (DD+)-D-0 invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the D* D scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the T-cc(+) is found to be close to unity, which implies that the T-cc(+) is a hadronic molecule generated by the interactions in the D*D-+(0) and D*D-0(+) channels. Employing heavy-quark spin symmetry, an isoscalar D* D* molecular partner of the T-cc(+) with J(P) = 1(+ )is predicted under the assumption that the DD* -D* D* coupled-channel effects can be neglected.
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Guo, F. K., Meissner, U. G., Nieves, J., & Yang, Z. (2016). Remarks on the P-c structures and triangle singularities. Eur. Phys. J. A, 52(10), 318–6pp.
Abstract: It was proposed that the narrow P-c(4450) structure observed by the LHCb Collaboration in the reaction Lambda(b) -> J/psi pK might be due to a triangle singularity around the chi(c1)-proton threshold at 4.45 GeV. We discuss the occurrence of a similar triangle singularity in the J/psi p invariant mass distribution for the decay Lambda(b) -> J/psi p pi, which could explain the bump around 4.45 GeV in the data. More precise measurements of this process would provide valuable information towards an understanding of the P-c structures.
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Albaladejo, M., Guo, F. K., Hidalgo-Duque, C., Nieves, J., & Pavon Valderrama, M. (2015). Decay widths of the spin-2 partners of the X(3872). Eur. Phys. J. C, 75(11), 547–26pp.
Abstract: We consider the X(3872) resonance as a J(PC) = 1(++) D (D) over bar* hadronic molecule. According to heavy quark spin symmetry, there will exist a partner with quantum numbers 2(++), X-2, which would be a D*(D) over bar* loosely bound state. The X-2 is expected to decay dominantly into D (D) over bar, D (D) over bar* and (D) over barD* in d-wave. In this work, we calculate the decay widths of the X-2 resonance into the above channels, as well as those of its bottom partner, X-b2, the mass of which comes from assuming heavy flavor symmetry for the contact terms. We find partial widths of the X-2 and X-b2 of the order of a few MeV. Finally, we also study the radiative X-2 -> D (D) over bar*gamma. and X-b2 -> (B) over bar B*gamma decays. These decay modes are more sensitive to the long-distance structure of the resonances and to the D (D) over bar* or B (B) over bar* final state interaction.
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Du, M. L., Guo, F. K., Meissner, U. G., & Yao, D. L. (2017). Study of open-charm 0(+) states in unitarized chiral effective theory with one-loop potentials. Eur. Phys. J. C, 77(11), 728–16pp.
Abstract: Chiral potentials are derived for the interactions between Goldstone bosons and pseudo-scalar charmed mesons up to next-to-next-to-leading order in a covariant chiral effective field theory with explicit vector charmed-meson degrees of freedom. Using the extended-on-mass-shell scheme, we demonstrate that the ultraviolet divergences and the so-called power counting breaking terms can be properly absorbed by the low-energy constants of the chiral Lagrangians. We calculate the scattering lengths by unitarizing the one-loop potentials and fit them to the data extracted from lattice QCD. The obtained results are compared to the ones without an explicit contribution of vector charmed mesons given previously. It is found that the difference is negligible for 5-wave scattering in the threshold region. This validates the use of D-*-less one-loop potentials in the study of the pertinent scattering lengths. We search for dynamically generated open-charm states with J(P) = 0(+) as poles of the 5-matrix on various Riemann sheets. The trajectories of those poles for varying pion masses are presented as well.
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Albaladejo, M., Guo, F. K., Hanhart, C., Meissner, U. G., Nieves, J., Nogga, A., et al. (2017). Note on X(3872) production at hadron colliders and its molecular structure. Chin. Phys. C, 41(12), 121001–3pp.
Abstract: The production of the X (3872) as a hadronic molecule in hadron colliders is clarified. We show that the conclusion of Bignamini et al., Phys. Rev. Lett. 103 (2009) 162001, that the production of the X(3872) at high pT implies a non-molecular structure, does not hold. In particular, using the well understood properties of the deuteron wave function as an example, we identify the relevant scales in the production process.
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Du, M. L., Filin, A., Baru, V., Dong, X. K., Epelbaum, E., Guo, F. K., et al. (2023). Role of Left-Hand Cut Contributions on Pole Extractions from Lattice Data: Case Study for Tcc(3875)+. Phys. Rev. Lett., 131(13), 131903–7pp.
Abstract: We discuss recent lattice data for the T_{cc}(3875)^{+} state to stress, for the first time, a potentially strong impact of left-hand cuts from the one-pion exchange on the pole extraction for near-threshold exotic states. In particular, if the left-hand cut is located close to the two-particle threshold, which happens naturally in the DD^{*} system for the pion mass exceeding its physical value, the effective-range expansion is valid only in a very limited energy range up to the cut and as such is of little use to reliably extract the poles. Then, an accurate extraction of the pole locations requires the one-pion exchange to be implemented explicitly into the scattering amplitudes. Our findings are general and potentially relevant for a wide class of hadronic near-threshold states.
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