arXiv subjects

Feng-Kun Guo

Publications and source records attributed to Feng-Kun Guo.

At least 127 records · Page 7Linked to original sources

arXiv2021

The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory

In the past, the axion-nucleon coupling has been calculated in the framework of SU(2) heavy baryon chiral perturbation theory up to third order in the chiral power counting. Here, we extend these earlier studies to the case of heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive the axion coupling to the full SU(3) baryon octet, showing that the axion also significantly couples to hyperons. As studies on dense nuclear matter suggest the possible existence of hyperons in stellar objects such as neutron stars, our results should have phenomenological implications related to the so-called axion window.

hep-ph↗

arXiv2021

Where is the lightest charmed scalar meson?

The lightest charmed scalar meson is known as the $D_0^*(2300)$, which is one of the earliest new hadron resonances observed at modern $B$ factories. We show here that the parameters assigned to the lightest scalar $D$-meson are in conflict with the precise LHCb data of the decay $B^-\to D^+ π^- π^-$. On the contrary, these data can be well described by an unitarized chiral amplitude containing a much lighter charmed scalar meson, the $D_0^*(2100)$. We also extract the low-energy $S$-wave $Dπ$ phase of the decay $B^-\to D^+ π^- π^-$ from the data in a model-independent way, and show that its difference from the $Dπ$ scattering phase shift can be traced back to an intermediate $ρ^-$ exchange. Our work highlights that an analysis of data consistent with chiral symmetry, unitarity, and analyticity is mandatory in order to extract the properties of the ground-state scalar mesons in the singly heavy sector correctly, in analogy to the light scalar mesons $f_0(500)$ and $K_0^*(700)$.

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arXiv2021

Two-Meson Form Factors in Unitarized Chiral Perturbation Theory

We present a comprehensive analysis of form factors for two light pseudoscalar mesons induced by scalar, vector, and tensor quark operators. The theoretical framework is based on a combination of unitarized chiral perturbation theory and dispersion relations. The low-energy constants in chiral perturbation theory are fixed by a global fit to the available data of the two-meson scattering phase shifts. Each form factor derived from unitarized chiral perturbation theory is improved by iteratively applying a dispersion relation. This study updates the existing results in the literature and explores those that have not been systematically studied previously, in particular the two-meson tensor form factors within unitarized chiral perturbation theory. We also discuss the applications of these form factors as mandatory inputs for low-energy phenomena, such as the semi-leptonic decays $B_s\to π^+π^-\ell^+\ell^-$ and the $τ$ lepton decay $τ\rightarrowπ^{-}π^{0}ν_τ$, in searches for physics beyond the Standard Model.

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arXiv2021

Explaining the Many Threshold Structures in the Heavy-Quark Hadron Spectrum

Tremendous progress has been made experimentally in the hadron spectrum containing heavy quarks in the last two decades. It is surprising that many resonant structures are around thresholds of a pair of heavy hadrons. There should be a threshold cusp at any $S$-wave threshold. By constructing a nonrelativistic effective field theory with open channels, we discuss the generalities of threshold behavior, and offer an explanation of the abundance of near-threshold peaks in the heavy quarkonium regime. We show that the threshold cusp can show up as a peak only for channels with attractive interaction, and the width of the cusp is inversely proportional to the reduced mass relevant for the threshold. We argue that there should be threshold structures at any threshold of a pair of heavy-quark and heavy-antiquark hadrons, which have attractive interaction at threshold, in the invariant mass distribution of a heavy quarkonium and light hadrons that couple to that open-flavor hadron pair. The structure becomes more pronounced if there is a near-threshold pole. Predictions of the possible pairs are also given for the ground state heavy hadrons. Precisely measuring the threshold structures will play an important role in revealing the heavy-hadron interactions, and thus understanding the puzzling hidden-charm and hidden-bottom structures.

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arXiv2021

On the nature of near-threshold bound and virtual states

Physical states are characterised uniquely by their pole positions and the corresponding residues. Accordingly, in those parameters also the nature of the states should be encoded. For bound states (poles on the real $s$-axis below the lowest threshold on the physical sheet) there is an established criterion formulated originally by Weinberg in the 1960s, which allows one to estimate the amount of compact and molecular components in a given state. We demonstrate in this paper that this criterion can be straightforwardly extended to shallow virtual states (poles on the real $s$-axis below the lowest threshold on the unphysical sheet) which should be classified as molecular. We argue that predominantly non-molecular or compact states exist either as bound states or as resonances (poles on the unphysical sheet off the real energy axis) but not as virtual states. We also discuss the limitations of the mentioned classification scheme.

hep-ph↗

arXiv2021

Strange molecular partners of the $Z_c(3900)$ and $Z_c(4020)$

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 $Z_c(4020)$ resonances, which have been theorized to be isovector $D^* \bar{D}$ and $D^* \bar{D}^*$ 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 $D^* \bar{D}_s$-$D \bar{D}_s^*$ and $D^* \bar{D}^{*}_s$ (or, equivalently, quark content $c\bar{c} s \bar{q}$, with $q = u, d$). The quantum numbers of these $Z_{cs}$ and $Z_{cs}^*$ resonances would be $I(J^P)$ = $\frac{1}{2}(1^+)$. The predicted masses of these partners depend on the details of the theoretical scheme used, but they should be around the $D^* \bar{D}_s$-$D \bar{D}_s^*$ and $D^* \bar{D}^{*}_s$ 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 $e^+e^-\to K^+(D_s^-D^{*0}+D_s^{*-}D^0)$.

hep-ph↗

arXiv2021

Triangle Singularities and Charmonium-like $XYZ$ States

The spectrum of hadrons is important for understanding the confinement of quantum chromodynamics. Many new puzzles arose since 2003 due to the abundance of experimental discoveries with the $XYZ$ structures in the heavy quarkonium mass region being the outstanding examples. Hadronic resonances correspond to poles of the $S$-matrix, which has other types of singularities such as the triangle singularity due to the simultaneous on-shellness of three intermediate particles. Here we briefly discuss a few possible manifestations of triangle singularities in the $XYZ$ physics, paying particular attention to the formalism that can be used to analyze the data for charged $Z_c$ structures in the $ψπ$ distributions of the reaction $e^+e^-\to ψπ^+π^-$.

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arXiv2021

Electron-Ion Collider in China

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of $\sim$80%) and protons (with a polarization of $\sim$70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2-3) $\times$ 10$^{33}$ cm$^{-2}$ s$^{-1}$. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC. The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies. This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

nucl-ex↗

arXiv2021

Graphic Method for Arbitrary $n$-body Phase Space

In quantum field theory, the phase space integration is an essential part in all theoretical calculations of cross sections and decay widths. It is also needed for computing the imaginary part of a physical amplitude. A key problem is to get the phase space formula expressed in terms of any chosen invariant masses in an $n$-body system. We propose a graphic method to quickly get the phase space formula of any given invariant masses intuitively for an arbitrary $n$-body system in general $D$-dimensional spacetime, with the involved momenta in any reference frame. The method also greatly simplifies the phase space calculation just as what Feynman diagrams do in calculating scattering amplitudes.

hep-ph↗

arXiv2020

Possible precise measurements of the $X(3872)$ mass with the $e^+e^-\toπ^0γX(3872)$ and $p\bar p\toγX(3872)$ reactions

It was recently proposed that the $X(3872)$ binding energy, the difference between the $D^0\bar D^{*0}$ threshold and the $X(3872)$ mass, can be precisely determined by measuring the $γX(3872)$ line shape from a short-distance $D^{*0}\bar D^{*0}$ source produced at high-energy experiments. Here, we investigate the feasibility of such a proposal by estimating the cross sections for the $e^+e^-\toπ^0γX(3872)$ and $p\bar p\toγX(3872)$ processes considering the $D^{*0}\bar D^{*0}D^0/\bar D^{*0}D^{*0}\bar D^0$ triangle loops. These loops can produce a triangle singularity slightly above the $D^{*0}\bar D^{*0}$ threshold. It is found that the peak structures originating from the $D^{*0}\bar D^{*0}$ threshold cusp and the triangle singularity are not altered much by the energy dependence introduced by the $e^+e^-\toπ^0D^{*0}\bar D^{*0}$ and $p\bar p\to\bar D^{*0}D^{*0}$ production parts or by considering a finite width for the $X(3872)$. We find that $σ(e^+e^-\toπ^0γX(3872)) \times {\rm Br}(X(3872)\toπ^+π^-J/ψ)$ is $\mathcal{O}(0.1~{\rm fb})$ with the $γX(3872)$ invariant mass integrated from 4.01 to 4.02 GeV and the c.m. energy of the $e^+e^-$ pair fixed at 4.23 GeV. The cross section $σ(p\bar p\toγX(3872))\times {\rm Br}(X(3872)\toπ^+π^-J/ψ)$ is estimated to be of $\mathcal{O}(10~{\rm pb})$. Our results suggest that a precise measurement of the $X(3872)$ binding energy can be done at PANDA.

hep-ph↗

arXiv2020

Generalized positivity bounds on chiral perturbation theory

Recently, a new set of positivity bounds with $t$ derivatives have been discovered. We explore the generic features of these generalized positivity bounds with loop amplitudes and apply these bounds to constrain the parameters in chiral perturbation theory up to the next-to-next-to-leading order. We show that the generalized positivity bounds give rise to stronger constraints on the $\bar l_i$ constants, compared to the existing axiomatic bounds. The parameter space of the $b_i$ constants is constrained by the generalized positivity bounds to be a convex region that is enclosed for many sections of the total space. We also show that the improved version of these positivity bounds can further enhance the constraints on the parameters. The often used Padé unitarization method however does not improve the analyticity of the amplitudes in the chiral perturbation theory at low energies.

hep-ph↗

arXiv2020

Exploring possible triangle singularities in the $Ξ^-_{b} \to K^- J/ψΛ$ decay

We analyze possible singularities in the $J/ψΛ$ invariant mass distribution of the $Ξ^-_{b}~\to~K^- J/ψΛ$ process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with $Ξ^*$-charmonium-$Λ$ intermediate states, the one from the $χ_{c1} Ξ(2120) Λ$ loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs $S$- and $P$-waves in $χ_{c1} Λ$ and $J/ψΛ$ systems, respectively, when the quantum numbers of these systems are $1/2^+$ or $3/2^+$. When the quantum numbers of the $Ξ(2120)$ are $J^P=1/2^+$, $1/2^-$ or $3/2^+$, the peak structure should be sharper than the other $J^P$ choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the $Ξ^*$-charmonium-$Λ$ triangle diagram if structures are observed in the $J/ψΛ$ invariant mass spectrum experimentally. In addition, a few triangle diagrams with the $D_{s1}^*(2700)$ as one of the intermediate particles can also produce singularities in the $J/ψΛ$ distribution, but at higher energies above 4.9 GeV.

hep-ph↗

arXiv2020

Deciphering the mechanism of near-threshold $J/ψ$ photoproduction

The photoproduction of the $J/ψ$ off the proton is believed to deepen our understanding of various physics issues. On the one hand, it is proposed to provide access to the origin of the proton mass, based on the QCD multipole expansion. On the other hand, it can be employed in a study of pentaquark states. The process is usually assumed to proceed through vector-meson dominance, that is the photon couples to a $J/ψ$ which rescatters with the proton to give the $J/ψp$ final state. In this Letter, we provide a compelling hint for and propose measurements necessary to confirm a novel production mechanism via the $Λ_c \bar D^{(*)}$ intermediate states. In particular, there must be cusp structures at the $Λ_c \bar D^{(*)}$ thresholds in the energy dependence of the $J/ψ$ photoproduction cross section. The same mechanism also implies the $J/ψ$-nucleon scattering lengths of order 1 mfm. Given this, one expects only a minor contribution of charm quarks to the nucleon mass.

hep-ph↗

arXiv2020

Selected Science Opportunities for the EicC

An electron ion collider has been proposed in China (EicC). It is anticipated that the facility would provide polarised electrons, protons and ion beams, in collisions with large centre-of-mass energy. This discussion highlights its potential to address issues that are central to understanding the emergence of mass within the Standard Model, using examples that range from the exploration of light-meson structure, through measurements of near-threshold heavy-quarkonia production, and on to studies of the spectrum of exotic hadrons.

hep-ph↗

arXiv2020

Extraction of $ND$ scattering lengths from the $Λ_b\rightarrowπ^-pD^0$ decay and properties of the $Σ_c(2800)^+$

The isovector and isoscalar $ND$ $s$-wave scattering lengths are extracted by fitting to the LHCb data of the $pD^0$ invariant-mass distribution in the decay $Λ_b\rightarrowπ^-pD^0$, making use of the cusp effect at the $nD^+$ threshold. The analysis is based on a coupled-channel nonrelativistic effective field theory. We find that the real part of the isovector $ND$ scattering length is unnaturally large due to the existence of a near-threshold state with a mass around 2.8 GeV. The state is consistent with the $Σ_c(2800)^+$ resonance observed at Belle. Our results suggest that it couples strongly to the $ND$ channel in an $s$-wave, and that its quantum numbers are $J^P=1/2^-$. The strong cusp behavior at the $nD^+$ threshold can be verified using updated LHCb data.

hep-ph↗

arXiv2020

Photoproduction of hidden-bottom pentaquark and related topics

Due to the discovery of the hidden-charm pentaquark $P_c$ states by the LHCb collaboration, the interests on the candidates of hidden-bottom pentaquark $P_b$ states are increasing. They are anticipated to exist as the analogues of the $P_c$ states in the bottom sector and predicted by many models. We give an exploration of searching for a typical $P_b$ in the $γp \to Υp$ reaction, which shows a promising potential to observe it at an electron-ion collider. The possibility of searching for $P_b$ in open-bottom channels are also briefly discussed. Meanwhile, the $t$-channel non-resonant contribution, which in fact covers several interesting topics at low energies, is systematically investigated.

hep-ph↗

arXiv2020

Triangle singularity in the $B^-\to K^-π^0X(3872)$ reaction and sensitivity to the $X(3872)$ mass

We have done a study of the $B^- \to K^- π^0 X(3872)$ reaction by means of a triangle mechanism via the chain of reactions: $B^- \to K^- D^{*0}\bar D^{*0}$; $D^{*0} \to π^0 D^0$; $D^0\bar D^{*0}\to X(3872)$. We show that this mechanism generates a triangle singularity in the $π^0 X(3872)$ 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 are 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 $D^0\bar D^{*0}$ threshold may be extracted from the asymmetry of the $π^0X$ line shape.

hep-ph↗

arXiv2020

Interpretation of the LHCb $P_c$ States as Hadronic Molecules and Hints of a Narrow $P_c(4380)$

Three hidden-charm pentaquark $P_c$ states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ were revealed in the $Λ_b^0\to J/ψp K^-$ process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the $J/ψp$ invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven $Σ_c^{(*)}\bar D^{(*)}$ molecular states in two spin multiplets, such that the $P_c(4312)$ is mainly a $Σ_c\bar D$ bound state with $J^P=1/2^-$, while $P_c(4440)$ and $P_c(4457)$ are $Σ_c\bar D^*$ bound states with quantum numbers $3/2^-$ and $1/2^-$, respectively. We also show that there is evidence for a narrow $Σ_c^*\bar D$ bound state in the data which we call $P_c(4380)$, different from the broad one reported by LHCb in 2015. With this state included, all predicted $Σ_c \bar D$, $Σ_c^* \bar D$, and $Σ_c \bar D^*$ hadronic molecules are seen in the data, while the missing three $Σ_c^*\bar D^*$ states are expected to be found in future runs of the LHC or in photoproduction experiments.

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