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., 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., Albaladejo, M., Guo, F. K., & Nieves, J. (2018). Heavy-to-light scalar form factors from Muskhelishvili-Omnes dispersion relations. Eur. Phys. J. C, 78(4), 310–26pp.
Abstract: By solving the Muskhelishvili-Omnes integral equations, the scalar form factors of the semileptonic heavy meson decays D -> pi(l) over bar nu(l), D -> (K) over bar(l) over bar nu(l), (K) over bar -> pi(l) over bar nu(l) and (B) over bar (s) -> Kl (nu) over bar (l) are simultaneously studied. As input, we employ unitarized heavy meson-Goldstone boson chiral coupled-channel amplitudes for the energy regions not far from thresholds, while, at high energies, adequate asymptotic conditions are imposed. The scalar form factors are expressed in terms of Omn\`es matrices multiplied by vector polynomials, which contain some undetermined dispersive subtraction constants. We make use of heavy quark and chiral symmetries to constrain these constants, which are fitted to lattice QCD results both in the charm and the bottom sectors, and in this latter sector to the light-cone sum rule predictions close to q(2)=0 as well. We find a good simultaneous description of the scalar form factors for the four semileptonic decay reactions. From this combined fit, and taking advantage that scalar and vector form factors are equal at q(2)=0, we obtain |V-cd| = 0.244 +/- 0.022, |V-cs| = 0.945 +/- 0.041 and |V-ub| = (4.3 +/- 0.7)x10(-3) for the involved Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. In addition, we predict the following vector form factors at q(2) = 0: |f(+)(D ->eta)(0)| = 0.01 +/- 0.05, |f(+)(Ds ->eta)(0)| = 0.50 +/- 0.08, |f(+)(Ds ->eta)(0)| = 0.73 +/- 0.03 and|f(+)((B) over bar ->eta)(0)| = 0.82 +/- 0.08, which might serve as alternatives to determine the CKM elements when experimental measurements of the corresponding differential decay rates become available. Finally, we predict the different form factors above the q(2)-regions accessible in the semileptonic decays, up to moderate energies amenable to be described using the unitarized coupled-channel chiral approach.
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Guo, F. K., Hidalgo-Duque, C., Nieves, J., Ozpineci, A., & Pavon Valderrama, M. (2014). Detecting the long-distance structure of the X(3872). Eur. Phys. J. C, 74(5), 2885–10pp.
Abstract: We study the decay within a molecular picture for the state. This decay mode is more sensitive to the long-distance structure of the resonance than its and decays, which are mainly controlled by the details of the wave function at short distances. We show that the final state interaction can be important, and that a precise measurement of this partial decay width can provide valuable information on the interaction strength between the charm mesons.
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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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Sakai, S., Oset, E., & Guo, F. K. (2020). Triangle singularity in the B-> K- pi X-0 (3872) reaction and sensitivity to the X(3872) mass. Phys. Rev. D, 101(5), 054030–10pp.
Abstract: We have done a study of the B--> K-pi X-0(3872) reaction by means of a triangle mechanism via the chain of reactions: B--> K-D*(0);(D) over bar*(0); D*(0)-> pi D-0(0); D-0(D) over bar*(0)-> X(3872). We show that this mechanism generates a triangle singularity in the pi X-0(3872) invariant mass for a very narrow window of the X(3872) mass, around the present measured values, and show that the peak positions and the shape of the mass distributions arc sensitive to the X(3872) mass, such that a measurement of the reaction can serve to improve on the present values of this mass. In particular, we point out that the X(3872) mass relative to the D-0(D) over bar*(0) threshold may be extracted from the asymmetry of the pi X-0 line shape.
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Yang, Z., Cao, X., Guo, F. K., Nieves, J., & Pavon Valderrama, M. (2021). Strange molecular partners of the Z(c)(3900) and Z(c)(4020). Phys. Rev. D, 103(7), 074029–8pp.
Abstract: Quantum chromodynamics presents a series of exact and approximate symmetries which can be exploited to predict new hadrons from previously known ones. The Z(c)(3900) and Z(c)(4020), which have been theorized to be isovector D*(D) over bar and D*(D) over bar* molecules [I-G(J(PC)) = 1(-)(1)(+-))], are no exception. Here we argue that from SU(3)-flavor symmetry, we should expect the existence of strange partners of the Z(c)'s with hadronic molecular configurations D*(D) over bar (s) – D (D) over bar*(s) and D*(D) over bar*(s) (or, equivalently, quark content c (c) over bars (q) over bar, with q = u, d). The quantum numbers of these Z(cs) and Z(cs)* structures would be I(J(P)) = 1/2 (1(+)). The predicted masses of these partners depend on the details of the theoretical scheme used, but they should be around the D*(D) over bar (s) – D (D) over bar*(s) and D*(D) over bar*(s) thresholds, respectively. Moreover, any of these states could be either a virtual pole or a resonance. We show that, together with a possible triangle singularity contribution, such a picture nicely agrees with the very recent BESIII data of the e(+)e(-) -> K+((Ds-D*0) + D*D--(s)0).
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Du, M. L., Baru, V., Guo, F. K., Hanhart, C., Meissner, U. G., Oller, J. A., et al. (2021). Revisiting the nature of the P-c pentaquarks. J. High Energy Phys., 08(8), 157–50pp.
Abstract: The nature of the three narrow hidden-charm pentaquark P-c states, i.e., P-c (4312), P-c (4440) and P-c (4457), is under intense discussion since their discovery from the updated analysis of the process Lambda(0)(b) -> I ) J/psi pK(-) by LHCb. In this work we extend our previous coupled-channel approach [Phys. Rev. Lett. 124, 072001 (2020)], in which the Pc states are treated as Sigma(()(c)*()) (D) over bar (()*()) molecules, by including the Lambda(c)(D) over bar (()*()) and eta(c)p as explicit inelastic channels in addition to the J/psi p, as required by unitarity and heavy quark spin symmetry (HQSS), respectively. Since inelastic parameters are very badly constrained by the current data, three calculation schemes are considered: (a) scheme I with pure contact interactions between the elastic, i.e., Sigma(()(c)*()) (D) over bar (()*()), and inelastic channels and without the Lambda(c)(D) over bar (()*()) interactions, (b) scheme II, where the one-pion exchange (OPE) is added to scheme I, and (c) scheme III, where the Lambda(c)(D) over bar (()*()) interactions are included in addition. It is shown that to obtain cutoff independent results, OPE in the multichannel system is to be supplemented with S-wave-to-D-wave mixing contact terms. As a result, in line with our previous analysis, we demonstrate that the experimental data for the J/psi p invariant mass distribution are consistent with the interpretation of the P-c(4312) and P-c(4440)/P-c(4457) as Sigma(c)(D) over bar and Sigma(c)(D) over bar* hadronic molecules, respectively, and that the data show clear evidence for a new narrow state, P-c(4380), identified as a Sigma(c)*(D) over bar molecule, which should exist as a consequence of HQSS. While two statistically equally good solutions are found in scheme I, only one of these solutions with the quantum numbers of the P-c (4440) and P-c (4457) being J(P) = 3/2(-) and 1/2(-), respectively, survives the requirement of regulator independence once the OPE is included. Moreover, we predict the line shapes in the elastic and inelastic channels and demonstrate that those related to the P-c (4440) and the P-c (4457) in the Sigma(()(c)*())<(D)over ( )anf eta(c)p mass distributions from Lambda(0)(b) ->( )Sigma(()(c)*()) (D) over barK(-) and Lambda(0)(b) -> eta(c)pK(-) will shed light on the quantum numbers of those states, once the data are available. We also investigate possible pentaquark signals in the Lambda(c)(D) over bar (()*()) final states.
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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., 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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