arXiv subjects

Han-Qing Zheng

Publications and source records attributed to Han-Qing Zheng.

At least 37 records · Page 2Linked to original sources

arXiv2021

An $N/D$ study of the $S_{11}$ channel $πN$ scattering amplitude

Extensive dynamical $N/D$ calculations are made in the study of $S_{11}$ channel low energy $π$N scatterings, based on various phenomenological model inputs of left cuts at tree level. The subtleties of the singular behavior of the partial wave amplitude at the origin of the complex $s$ plane are carefully analysed. Furthermore, { it is found that the dispersion representation for the phase shift, $δ$, has to be modified in the case of $π$N scatterings. An additional contribution from the dispersion integral exists, which is, however, almost exactly cancelled the contribution from two virtual poles located near the end points of the segment cut induced by $u$ channel nucleon exchanges.} Relying very little on the details of the dynamical inputs, the subthreshold resonance $N^*(890)$ survives.

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arXiv2021

X_1(2900) as a D_1 K molecule

The analyses of the LHCb data on X(2900) in the D^- K^+ spectrum are performed. Both dynamically generated and explicitly introduced X_1(2900) are considered. The results show that both these two approaches support the interpretation of X_1(2900) as a bar{D}_1 K molecular state, with J^{P}=1^- and an iso-singlet interpretation is much more favorable. The effect of triangle singularity on the production of X_1(2900) is also discussed, and it is found that it cannot be interpreted as a pure triangle cusp.

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arXiv2021

Some remarks on $X(6900)$

The analysis of the LHCb data on $X(6900)$ found in the di-$\jpsi$ system is performed using a momentum-dependent Flatté-like parameterization. The use of the pole counting rule and spectral density function sum rule give consistent conclusions that both confining states and molecular states are possible, or it is unable to distinguish the nature of $X(6900)$, if only the di-$\jpsi$ experimental data with current statistics are available. Nevertheless, we found that the lowest state in the di-$J/ψ$ system has very likely the same quantum numbers as $X(6900)$, and $X(6900)$ is probably not interpreted as a $J/ψ-ψ(2S)$ molecular state.

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arXiv2021

Dispersive analysis of low energy $γ^* N\rightarrowπN$ process

We use a dispersion representation based on unitarity and analyticity to study the low energy $γ^* N\rightarrow πN$ process in the $S_{11}$ channel. Final state interactions among the $πN$ system are critical to this analysis. The left-hand part of the partial wave amplitude is imported from $\mathcal{O}(p^2)$ chiral perturbation theory result. On the right-hand part, the final state interaction is calculated through Omnès formula in $S$ wave. It is found that a good numerical fit can be achieved with only one subtraction parameter, and the eletroproduction experimental data of multipole amplitudes $E_{0+},\ S_{0+}$ in the energy region below $Δ(1232)$ are well described when the photon virtuality $Q^2 \leq 0.1 \mathrm{GeV}^2$.

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arXiv2021

A Review on Partial-wave Dynamics with Chiral Effective Field Theory and Dispersion Relation

The description of strong interaction physics of low-lying resonances is out of the valid range of perturbative QCD. Chiral effective field theories have been developed to tackle the issue. Partial wave dynamics is the systematic tool to decode the underlying physics and reveal the properties of those resonances. It is extremely powerful and helpful for our understanding of the non-perturbative regime, especially when dispersion techniques are utilized simultaneously. Recently, plenty of exotic/ordinary hadrons have been reported by experiment collaborations, e.g. LHCb, Belle, and BESIII, etc.. In this review, we summarize the recent progress on the applications of partial wave dynamics combined with chiral effective field theories and dispersion relations, on related topics, with emphasis on $ππ$, $πK$, $πN$ and $\bar{K}N$ scatterings.

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arXiv2021

On leptonic width of $X(4260)$

New measurements on cross sections in $e^+e^-\to J/ψπ^+π^-$, $h_cπ^+π^-$, $D^0D^{*-}π^++c.c.$, $ψ(2S)π^+π^-$, $ωχ_{c0}$ and $J/ψη$ channels have been carried out by BESIII, Belle and BABAR collaborations, and also in the $D_s^*\bar D_s^*$ channel. We perform extensive numerical analyses by combining all these data available, together with those in $D\bar D^*$ and $D^*\bar D^*$ channels. Though the latter show no evident peak around $\sqrt{s}=4.230$ GeV, the missing $X(4260)$ is explained as that it is concealed by the interference effects of the well established charmonia $ψ(4040)$, $ψ(4160)$ and $ψ(4415)$. Our analyses reveal that the leptonic decay width of $X(4260)$ ranges from $O(10^2)$ eV to $O(1)$ keV, and hence may be explained in the conventional quark model picture. That is, the $X(4260)$ may well be interpreted as a mixture of $4^3S_1$ and $3^3D_1$ states.

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arXiv2020

Dispersive Analysis of Low Energy $γN\toπN$ Process and Studies on the $N^*(890)$ Resonance

We present a dispersive representation of the $γN\rightarrow πN$ partial-wave amplitude based on unitarity and analyticity. In this representation, the right-hand-cut contribution responsible for $πN$ final-state-interaction effect are taken into account via an Omnés formalism with elastic $πN$ phase shifts as inputs, while the left-hand-cut contribution is estimated by invoking chiral perturbation theory. Numerical fits are performed in order to pin down the involved subtraction constants. It is found that good fit quality can be achieved with only one free parameter and the experimental data of the multipole amplitude $E_{0}^+$ in the energy region below the $Δ(1232)$ are well described. Furthermore, we extend the $γN\rightarrow πN$ partial-wave amplitude to the second Riemann sheet so as to extract the couplings of the $N^\ast(890)$. The modulus of the residue of the multipole amplitude $E_{0}^+$ ($S_{11pE}$) is $2.41\rm{mfm\cdot GeV^2}$ and the partial width of $N^*(890)\toγN$ at the pole is about $0.369\ {\rm MeV}$, which is almost the same as the one of $N^*(1535)$, indicating that $N^\ast(890)$ strongly couples to $πN$ system.

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arXiv2020

How does the $S_{11}$ $N^*(890)$ state emerge from a naive $K$ matrix fit?

We give a pedagogical analysis on $K$ matrix models describing the $πN$ scattering amplitude, in $S_{11}$ channel at low energies. We show how the correct use of analyticity in the $s$ channel and crossing symmetry in $t$ and $u$ channels leads to a much improved analytic behavior in the negative $s$ region, in agreement with the prediction from chiral perturbation amplitudes in its validity region. The analysis leads again to the conclusion that a genuine $N^*(890)$ resonance exists.

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arXiv2019

Discussions on the Line-shape of $X(4660)$ Resonance

A careful reanalysis is made on $e^+e^-\to X(4660)\to (Λ_c\barΛ_c)/(ψ'ππ)$ processes, aiming at resolving the apparent conflicts between Belle and BESIII data above $Λ_c\barΛ_c$ threshold. We use a model containing a Breit-Wigner resonance and $Λ_c\barΛ_c$ four-point contact interactions, with which the enhancement right above the $Λ_c\barΛ_c$ threshold is well explained by a virtual pole generated by $Λ_c\barΛ_c$ attractive final state interaction, located at $M_V=4.566\pm0.007$ GeV. Meanwhile, $X(4660)$ remains to be a typical Breit-Wigner resonance, and is hence of confinement nature. Our analysis strongly suggests the existence of the virtual pole with statistical significance of $4.2$ standard deviation ($σ$). Nevertheless, the conclusion crucially depends on the line-shape of cross sections which are of limited statistics, hence we urge new experimental analyses from Belle II, BESIII, and LHCb to settle the issue.

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arXiv2019

New Insights on Low Energy $πN$ Scattering Amplitudes: Comprehensive Analyses at $\mathcal{O}(p^3)$ Level

A production representation of partial-wave $S$ matrix is utilized to construct low-energy elastic pion-nucleon scattering amplitudes from cuts and poles on complex Riemann sheets. Among them, the contribution of left-hand cuts is estimated using the $\mathcal{O}(p^3)$ results obtained in covariant baryon chiral perturbation theory within the extended-on-nass-shell scheme. By fitting to data on partial-wave phase shifts, it is indicated that the existences of hidden poles in $S_{11}$ and $P_{11}$ channels, as conjectured in our previous paper~\citep{Wang:2017agd}, are firmly established. Specifically, the pole mass of the $S_{11}$ hidden resonance is determined to be $(895\pm81)-(164\pm23)i$ MeV, whereas, the virtual pole in the $P_{11}$ channel locates at $(966\pm18)$ MeV. It is found that analyses at the $\mathcal{O}(p^3)$ level improves significantly the fit quality, comparing with the previous $\mathcal{O}(p^2)$ one. Quantitative studies with cautious physical discussions are also conducted for the other $S$- and $P$-wave channels.

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arXiv2018

On the Existence of $N^*(890)$ Resonance in $S_{11}$ Channel of $πN$ Scatterings

Low-energy partial-wave $πN$ scattering data is reexamined with the help of the production representation of partial-wave $S$ matrix, where branch cuts and poles are thoroughly under consideration. The left-hand cut contribution to the phase shift is determined, with controlled systematic error estimates, by using the results of $\mathcal{O}(p^3)$ chiral perturbative amplitudes obtained in the extended-on-mass-shell scheme. In $S_{11}$ and $P_{11}$ channels, severe discrepancies are observed between the phase shift data and the sum of all known contributions. Statistically satisfactory fits to the data can only be achieved by adding extra poles in the two channels. We find that a $S_{11}$ resonance pole locates at $\sqrt{z_{r}}=(0.895\pm0.081)-(0.164\pm0.023)i$ GeV, on the complex $s$-plane. On the other hand, a $P_{11}$ virtual pole, as an accompanying partner of the nucleon bound-state pole, locates at $\sqrt{z_{v}}=(0.966\pm0.018)$ GeV, slightly above the nucleon pole on the real axis below threshold. Physical origin of the two newly established poles is explored to the best of our knowledge. It is emphasized that the $\mathcal{O}(p^3)$ calculation greatly improves the fit quality comparing with the previous $\mathcal{O}(p^2)$ one.

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arXiv2018

New Insights on Low Energy $πN$ Scattering Amplitudes

The $S$- and $P$- wave phase shifts of low-energy pion-nucleon scatterings are analysed using Peking University representation, in which they are decomposed into various terms contributing either from poles or branch cuts. We estimate the left-hand cut contributions with the help of tree-level perturbative amplitudes derived in relativistic baryon chiral perturbation theory up to $\mathcal{O}(p^2)$. It is found that in $S_{11}$ and $P_{11}$ channels, contributions from known resonances and cuts are far from enough to saturate experimental phase shift data -- strongly indicating contributions from low lying poles undiscovered before, and we fully explore possible physics behind. On the other side, no serious disagreements are observed in the other channels.

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arXiv2017

A study of $ρ-ω$ mixing in resonance chiral theory

The strong and electromagnetic corrections to $ρ-ω$ mixing are calculated using a SU(2) version of resonance chiral theory up to next-to-leading orders in $1/N_C$ expansion, respectively. Up to our accuracy, the effect of the momentum dependence of $ρ-ω$ mixing is incorporated due to the inclusion of loop contributions. We analyze the impact of $ρ-ω$ mixing on the pion vector form factor by performing numerical fit to the data extracted from $e^+e^-\rightarrow π^+π^-$ and $τ\rightarrow ν_τ2π$, while the decay width of $ω\rightarrow π^+π^-$ is taken into account as a constraint. It is found that the momentum dependence is significant in a good description of the experimental data. In addition, based on the fitted values of the involved parameters, we analyze the decay width of $ω\rightarrow π^+π^-$, which turns out to be highly dominated by the $ρ-ω$ mixing effect.

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arXiv2017

The $Z_c(3900)$ peak does not come from the "triangle singularity"

We compare contributions from the triangle diagram and the $D\bar D^*$ bubble chain to the processes of $e^{+}e^{-}\rightarrow J/ψπ^{+}π^{-}$ and $e^{+}e^{-}\rightarrow (D\bar D^*)^\mpπ^{\pm}$. By fitting the $J/ψπ$ maximum spectrum and the $D\bar D^*$ spectrum, we find that the triangle diagram cannot explain the new data from BESIII Collaboration at center of mass at 4.23GeV and 4.26GeV, simultaneously. On the contrary, the molecular assignment of $Z_c(3900)$ gives a much better description.

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arXiv2016

$Z_c(3900)$ as a $D\bar{D}^*$ molecule from the pole counting rule

A comprehensive study on the nature of the $Z_c(3900)$ resonant structure is carried out in this work. By constructing the pertinent effective Lagrangians and considering the important final-state-interaction effects, we first give a unified description to all the relevant experimental data available, including the $J/ψπ$ and $ππ$ invariant mass distributions from the $e^+e^-\to J/ψππ$ process, the $h_cπ$ distribution from $e^+e^-\to h_cππ$ and also the $D\bar D^{*}$ spectrum in the $e^+e^-\to D\bar D^{*}π$ process. After fitting the unknown parameters to the previous data, we search the pole in the complex energy plane and find only one pole in the nearby energy region in different Riemann sheets. Therefore we conclude that $Z_c(3900)$ is of $D\bar D^*$ molecular nature, according to the pole counting rule method~[Nucl.~Phys.~A543, 632 (1992); Phys.~Rev.~D 35,~1633 (1987)]. We emphasize that the conclusion based upon the pole counting method is not trivial, since both the $D\bar D^{*}$ contact interactions and the explicit $Z_c$ exchanges are introduced in our analyses and they lead to the same conclusion.

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arXiv2014

A Refined Analysis on the $X(3872)$ Resonance

We study the property of the $X(3872)$ meson by analyzing the $B\to K D\bar D^*$ and $B\to K J/ψπ^+π^-$ decay processes. The competition between the rescattering mediated through a Breit-Wigner resonance and the rescattering generated from a local $D\bar{D}^* \to D\bar{D}^*$ interaction is carefully studied through an effective lagrangian approach. Three different fits are performed: pure Breit-Wigner case, pure $D\bar{D}^*$ molecule case with only local rescattering vertices (generated by the loop chain), and the mixed case. It is found that data supports the picture where X(3872) is mainly a ($\bar cc$) Breit-Wigner resonance with a small contribution to the self-energy generated by $\bar DD^*$ final state interaction. For our optimal fit, the pole mass and width are found to be: $M_X=3871.2\pm0.7$MeV and $Γ_X=6.5\pm1.2$MeV.

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arXiv2014

Radiative transition processes of light vector resonances in a chiral framework

Within the framework of chiral effective field theory, we study various electromagnetic processes with light vector resonances: $K^{\ast}(892)\to Kγ$, $e^{+}e^{-}\to K^{\ast}(892)K $ and the $ωπγ^\ast$ form factors. With two multiplets of vector resonances being introduced, we fit the decay widths of $K^{\ast0}\to K^{0}γ$, $K^{\ast+}\to K^{+}γ$, and the pertinent measurements from the $e^{+}e^{-}\to K^{\ast \pm}(892)K^{\mp} $ cross sections, such as moduli and relative phases between the isoscalar and isovector components from BABAR collaboration, together with the $ωπ$ form factors from NA60, SND and CLEO collaborations. The values of resonance couplings, masses and widths of the excited vector states $ρ'$ and $ϕ'$ are then determined. The $ω'$-$ϕ'$ mixing angle is discussed and turns out to be quite different from the ideal mixing case. Three sources of $SU(3)$ symmetry breaking effects in the $Γ(K^{\ast}\to Kγ)$ decays are identified and analyzed in detail.

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arXiv2013

Positivity constraints on the low-energy constants of the chiral pion-nucleon Lagrangian

Positivity constraints on the pion-nucleon scattering amplitude are derived in this article with the help of general S-matrix arguments, such as analyticity, crossing symmetry and unitarity, in the upper part of Mandelstam triangle, R. Scanning inside the region R, the most stringent bounds on the chiral low energy constants of the pion-nucleon Lagrangian are determined. When just considering the central values of the fit results from covariant baryon chiral perturbation theory using extended-on-mass-shell scheme, it is found that these bounds are well respected numerically both at O(p^3) and O(p^4) level. Nevertheless, when taking the errors into account, only the O(p^4) bounds are obeyed in the full error interval, while the bounds on O(p^3) fits are slightly violated. If one disregards loop contributions, the bounds always fail in certain regions of R. Thus, at a given chiral order these terms are not numerically negligible and one needs to consider all possible contributions, i.e., both tree-level and loop diagrams. We have provided the constraints for special points in R where the bounds are nearly optimal in terms of just a few chiral couplings, which can be easily implemented and employed to constrain future analyses. Some issues about calculations with an explicit Delta(1232) resonance are also discussed.

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