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Ji, T., Dong, X. K., Albaladejo, M., Du, M. L., Guo, F. K., Nieves, J., et al. (2023). Understanding the 0(++) and 2(++) charmonium(-like) states near 3.9 GeV. Sci. Bull., 68(7), 688–697.
Abstract: We propose that the X(3915) observed in the J/psi x channel is the same state as the chi(c2)(3930), and the X(3960), observed in the Ds+Ds- channel, is an S-wave Ds+Ds- hadronic molecule. In addition, the J(PC) = 0(++) component in the B+ -> D+D-K+ assigned to the X(3915) in the current Review of Particle Physics has the same origin as the X(3960), which has a mass around 3.94 GeV. To check the proposal, the available data in the D (D) over bar and Ds+Ds- channels from both B decays and gamma gamma fusion reaction are analyzed considering both the D (D) over bar -D-s(D) over bar (s)-D*(D) over bar*-D-s*(D) over bar (s)* coupled channels with 0(++) and a 2(++) state introduced additionally. It is found that all the data in different processes can be simultaneously well reproduced, and the coupled-channel dynamics produce four hidden-charm scalar molecular states with masses around 3.73, 3.94, 3.99 and 4.23 GeV, respectively. The results may deepen our understanding of the spectrum of charmonia as well as of the interactions between charmed hadrons.
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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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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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Guo, F. K., Hidalgo-Duque, C., Nieves, J., & Pavon Valderrama, M. (2013). Consequences of heavy-quark symmetries for hadronic molecules. Phys. Rev. D, 88(5), 054007–5pp.
Abstract: Among the newly observed structures in the heavy-quarkonium mass region, some have been proposed to be hadronic molecules. We investigate the consequences of heavy- quark flavor symmetry on these heavy meson hadronic molecules. The symmetry allows us to predict new hadronic molecules on one hand, and test the hadronic molecular assumption of the observed structures on the other hand. We explore the consequences of the flavor symmetry assuming the X(3872) and Z(b)(10 610) as an isoscalar D (D) over bar* and isovector B (B) over bar* hadronic molecule, respectively. A series of hadronic molecules composed of heavy mesons are predicted. In particular, there is an isoscalar 1(++) B (B) over bar* bound state with a mass about 10 580 MeV which may be searched for in the Y(1S, 2S)pi(+) pi(-) pi(0) mass distribution; the isovector charmonium partners of the Z(b)(10 610) and the Z(b)(10 650) are also predicted, which probably corresponds to the very recently observed Z(c)(3900) and Z(c)(4025) resonances by the BESIII Collaboration.
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Guo, F. K., Hidalgo-Duque, C., Nieves, J., & Pavon Valderrama, M. (2013). Heavy-antiquark-diquark symmetry and heavy hadron molecules: Are there triply heavy pentaquarks? Phys. Rev. D, 88(5), 054014–6pp.
Abstract: We explore the consequences of heavy flavor, heavy quark spin, and heavy antiquark-diquark symmetries for hadronic molecules within an effective field theory framework. Owing to heavy antiquark-diquark symmetry, the doubly heavy baryons have approximately the same light-quark structure as the heavy antimesons. As a consequence, the existence of a heavy meson-antimeson molecule implies the possibility of a partner composed of a heavy meson and a doubly heavy baryon. In this regard, the D (D) over bar* molecular nature of the X(3872) will hint at the existence of several baryonic partners with isospin I = 0 and J(P) = 5(-)/2 or 3(-)/2. Moreover, if the Z(b)(10650) turns out to be a B*(B) over bar* bound state, we can be confident of the existence of Xi(bb)*(B) over bar* hadronic molecules with quantum numbers I(J(P)) = 1(1(-)/2) and I(J(P)) = 1(3/2(-)). These states are of special interest since they can be considered to be triply heavy pentaquarks.
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Bayar, M., Aceti, F., Guo, F. K., & Oset, E. (2016). Discussion on triangle singularities in the Lambda(b) -> J/psi K(-)p reaction. Phys. Rev. D, 94(7), 074039–10pp.
Abstract: We have analyzed the singularities of a triangle loop integral in detail and derived a formula for an easy evaluation of the triangle singularity on the physical boundary. It is applied to the Lambda(b) -> J/psi K(-)p process via Lambda*-charmonium-proton intermediate states. Although the evaluation of absolute rates is not possible, we identify the chi(c1) and the psi(2S)as the relatively most relevant states among all possible charmonia up to the psi(2S). The Lambda(1890)chi(c1)p loop is very special, as its normal threshold and triangle singularities merge at about 4.45 GeV, generating a narrow and prominent peak in the amplitude in the case that the chi(c1)p is in an S wave. We also see that loops with the same charmonium and other Lambda* hyperons produce less dramatic peaks from the threshold singularity alone. For the case of chi(c1)p -> J/psi p and quantum numbers 3/2(-) or 5/2(+), one needs P and D waves, respectively, in the chi(c1)p, which drastically reduce the strength of the contribution and smooth the threshold peak. In this case, we conclude that the singularities cannot account for the observed narrow peak. In the case of 1/2(+), 3/2(-) quantum numbers, where chi(c1)p -> J/psi p can proceed in an S wave, the Lambda(1890)chi(c1)p triangle diagram could play an important role, though neither can assert their strength without further input from experiments and lattice QCD calculations.
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Du, M. L., Albaladejo, M., Fernandez-Soler, P., Guo, F. K., Hanhart, C., Meissner, U. G., et al. (2018). Towards a new paradigm for heavy-light meson spectroscopy. Phys. Rev. D, 98(9), 094018–8pp.
Abstract: Since 2003 many new hadrons, including the lowest-lying positive-parity charm-strange mesons D*(s0) (2317) and D-s1 (2460), have been observed that do not conform with quark-model expectations. It was recently demonstrated that various puzzles in the charm-meson spectrum find a natural resolution if the SU(3) multiplets for the lightest scalar and axial-vector states, among them the D*(s0) (2317) and the D-s1 (2460), owe their existence to the nonperturbative dynamics of Goldstone-boson scattering off D-(s) and D*((s)) mesons. Most importantly the ordering of the lightest strange and nonstrange scalars becomes natural. We demonstrate for the first time that this mechanism is strongly supported by the recent high quality data on the B- -> D+ pi(-)pi(-) provided by the LHCb experiment. This implies that the lowest quark-model positive-parity charm mesons, together with their bottom counterparts, if realized in nature, do not form the ground-state multiplet. This is similar to the pattern that has been established for the scalar mesons made from light up, down, and strange quarks, where the lowest multiplet is considered to be made of states not described by the quark model. In a broader view, the hadron spectrum must be viewed as more than a collection of quark-model states.
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Yao, D. L., Fernandez-Soler, P., Guo, F. K., & Nieves, J. (2020). New parametrization of the form factors in (B)over-bar -> Dl(nu)over-bar(l) decays. Phys. Rev. D, 101(3), 034014–7pp.
Abstract: A new model-independent parametrization is proposed for the hadronic form factors in the semileptonic (B) over bar -> Dl (nu) over bar (l) decay. By a combined consideration of the recent experimental and lattice QCD data, we determine precisely the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar = 41.01(75) x 10(-3) and the ratio R-D = BR((B) over bar -> D tau(nu) over bar (tau))/BR((B) over bar -> Dl (nu) over bar (l)) = 0.301(5). The coefficients in this parametrization, related to phase shifts by sumrulelike dispersion relations and hence called phase moments, encode important scattering information of the (B) over bar (D) over bar interactions which are poorly known so far. Thus, we give strong hints about the existence of at least one bound and one virtual (B) over bar (D) over bar S-wave 0(+) states, subject to uncertainties produced by potentially sizable inelastic effects. This formalism is also applicable for any other semileptonic processes induced by the weak b -> c transition.
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