arXiv subjects

Zhi-Yong Zhou

Publications and source records attributed to Zhi-Yong Zhou.

32 records · Page 2Linked to original sources

arXiv2020

Does the bottomonium counterpart of $X(3872)$ exist?

A narrow line shape peak at about 10615 MeV, just above the threshold in the $B\bar B^*$ channel, which can be regarded as the signal of bottomonium counterpart of $X(3872)$, $X_b$, is predicted by using the extended Friedrichs scheme. Though a virtual state is found at about 10593 MeV in this scheme, we point out that the peak is contributed mainly by the coupling form factor, which comes from the convolution of the interaction term and meson wave functions including the one from $χ_{b1}(4P)$, but not mainly by the virtual-state pole. In this picture, the reason why $X_b$ signal is not observed in the $Υπ^+π^-$ and $Υπ^+π^-π^0$ channels can also be understood. The $χ_{b1}(4P)$ mass and width are found to be about 10771 MeV and 6 MeV, respectively and a dynamically generated broad resonance is also found with its mass and width at about 10672 MeV and 78 MeV, respectively. The line shapes of these two states are also affected by the form factor effect. Thus, this study also emphasizes the importance of the structure of the wave functions of high radial excitations in the analysis of the line shapes, and provides a caveat that some signals may be generated from the structures of the form factors rather than from poles.

hep-ph↗

arXiv2019

Possible molecular states in $B^{()}B^{()}$ scatterings

We present that, if unitarizing the $B^{(*)}B^{(*)}$ scattering amplitudes in the constituent interchange model, one can find two bound state poles for $(I_{tot},S_{tot})=(0,1)$ $BB^*$ and $B^*B^*$ system, which corresponds to two $I(J^P)=0(1^+)$ doubly bottomed molecular states. Furthermore, it is noticed that the virtual states in $(1,0)$ $BB$, $(1,1)$ $BB^*$, $(1,0)$ $B^*B^*$, and $(1,2)$ $B^*B^*$ systems could produce enhancements of the module squares of the scattering $T$-matrix just above the related thresholds, which might correspond to $I(J^P)=1(0^+)$, $1(1^+)$, and $1(2^+)$ doubly bottomed molecular states, respectively. The calculation may be helpful for searching for the doubly bottomed molecular state in future experiments.

hep-ph↗

arXiv2019

Understanding $X(3872)$ and its decays in the extended Friedrichs scheme

We present that the $X(3872)$ could be represented as a dynamically generated state in the extended Friedrichs scheme, in which the ratio of "elementariness" and "compositeness" of the different components in the $X(3872)$ is about $Z_{c\bar c}:X_{\bar D^0 D^{0*}}: X_{ D^+ D^{-*}}: X_{\bar D^* D^*}$ $= 1:(2.67\sim 8.85):(0.45\sim 0.46):0.04$. Furthermore, its decays to $π^0$ and a $P$-wave charmonium $χ_{cJ}$ state with $J=0,1$, or $2$, $J/ψπ^+π^-$, and $J/ψπ^+π^-π^0$ could be calculated out with the help of Barnes-Swanson model. The isospin breaking effects is easily understood in this scheme. This calculation also shows that the decay rate of $X(3872)$ to $χ_{c1}π^0$ is much smaller than its decay rate to $J/ψπ^+π^-$.

hep-ph↗

arXiv2019

$D$ wave charmonia

Inspired by the recent observations of the vector charmonium-like states at BES III Collaboration and $ψ(3842)$ at LHCb Collaboration, we comb the $D$ wave charmonium state in the present work. We first evaluate the possibility of $Y(4320)$ as $ψ(3^3D_1)$ by investigating its open charm decays in quark-pair creation model and we find the width of $Y(4320)$ can be reproduced in a reasonable parameter range. Moreover, we take $ψ(3770)$, $ψ(4160)$ and $Y(4320)$ as the scale of $1D$, $2D$ and $3D$ charmonia to estimate the open charm decays of other $D$ wave charmonia. The total and partial widths of $D$ wave charmonium states have been predicted, which could be tested by further measurements at LHCb and Belle II Collaborations.

hep-ph↗

arXiv2017

Comprehending Isospin breaking effects of $X(3872)$ in a Friedrichs-model-like scheme

Recently, we have shown that the $X(3872)$ state can be naturally generated as a bound state by incorporating the hadron interactions into the Godfrey-Isgur quark model using the Friedrichs-like model combined with the QPC model, in which the wave function for the $X(3872)$ as a combination of the bare $c\bar c$ state and the continuum states can also be obtained. Under this scheme, we now investigate the isospin breaking effect of $X(3872)$ in its decays to $J/ψπ^+π^-$ and $J/ψπ^+π^-π^0$. By Considering its dominant continuum parts coupling to $J/ψρ$ and $J/ψω$ through the quark rearrangement process, one could obtain the reasonable ratio of $\mathcal{B}(X(3872)\rightarrow J/ψπ^+π^-π^0)/\mathcal{B}(X(3872)\rightarrow J/ψπ^+π^-)\simeq (0.58\sim 0.92)$. It is also shown that the $\bar D D^*$ invariant mass distributions in the $B\rightarrow \bar D D^* K$ decays could be understood qualitatively at the same time. This scheme may provide more insight to understand the enigmatic nature of the $X(3872)$ state.

hep-ph↗

arXiv2017

Understanding $X(3862)$, $X(3872)$, and $X(3930)$ in a Friedrichs-model-like scheme

We developed a Friedrichs-model-like scheme in studying the hadron resonance phenomenology and present that the hadron resonances might be regarded as the Gamow states produced by a Hamiltonian in which the bare discrete state is described by the result of usual quark potential model and the interaction part is described by the quark pair creation model. In a one-parameter calculation, the $X(3862)$, $X(3872)$, and $X(3930)$ state could be simultaneously produced with a quite good accuracy by coupling the three P-wave states, $χ_{c2}(2P)$, $χ_{c1}(2P)$, $χ_{c0}(2P)$ predicted in the Godfrey-Isgur model to the $D\bar D$, $D\bar D^{*}$, $D^*\bar D^*$ continuum states. At the same time, we predict that the $h_c(2P)$ state is at about 3902 MeV with a pole width of about 54 MeV. In this calculation, the $X(3872)$ state has a large compositeness. This scheme may shed more light on the long-standing problem about the general discrepancy between the prediction of the quark model and the observed values, and it may also provide reference for future search for the hadron resonance state.

hep-ph↗

arXiv2017

Partial Wave Decomposition in Friedrichs Model With Self-interacting Continua

We consider the nonrelativistic model of coupling bare discrete states with continuum states in which the continuum states can have interactions among themselves. By partial-wave decomposition and constraint to the conserved angular momentum eigenstates, the model can be reduced to Friedrichs-like model with additional interactions between the continua. If a kind of factorizable form factor is chosen, the model can be exactly solvable, that is, the generalized discrete eigenstates including bound states, virtual states, and resonances, can all be represented using the original bare states, and so do the in-state and out-state. The exact $S$ matrix is thus obtained. We then discuss the behaviors of the dynamically generated $S$-wave and $P$-wave discrete states as the coupling is varying when there is only one self-interacting bare continuum state. We find that even when the potential is repulsive there could also be resonances and virtual states. In the $P$-wave cases with attractive interaction, we find that when there is a near-threshold bound state, there will always be an accompanying virtual state and we also give a more general argument of this effect.

hep-ph↗

arXiv2017

On Friedrichs Model with Two Continuum States

The Friedrichs model with one discrete state coupled to more than one continuum is studied. The exact eigenstates for the full Hamiltonian can be solved explicitly. The discrete state is found to generate more than one virtual state pole or more than one pair of resonance poles in different Riemann sheets in different situations. The form factors could also generate new states on different sheets. All these states can appear in the generalized completeness relation.

hep-ph↗

arXiv2016

Virtual states and generalized completeness relation in the Friedrichs Model

We study the well-known Friedrichs model, in which a discrete state is coupled to a continuum state. By examining the pole behaviors of the Friedrichs model in a specific form factor thoroughly, we find that, in general, when the bare discrete state is below the threshold of the continuum state, there should also be a virtual-state pole accompanying the bound-state pole originating from the bare discrete state as the coupling is turned on. There are also other second-sheet poles originating from the singularities of the form factor. We give a general argument for the existence of these two kinds of states. As the coupling is increased to a certain value, the second-sheet poles may merge and become higher-order poles. We then discuss the completeness relations incorporating bound states, virtual states, and resonant states corresponding to higher-order poles.

hep-ph↗

arXiv2015

Could the $X(3915)$ and the $X(3930)$ Be the Same Tensor State?

By using a combined amplitude analysis of the $γγ\rightarrow D\bar{D}$ and $γγ\rightarrow J/ψω$ data, we demonstrate that the $X(3915)$, which is quoted as a $J^{PC}=0^{++}$ state in the Particle Data Group table, is favored by the data to be a $J^{PC}=2^{++}$ state appearing in both channels, which means that the $X(3915)$ and the $X(3930)$ can be regarded as the same $J^{PC}=2^{++}$ state. Meanwhile, the data also prefer a large helicity-0 contribution of this tensor resonance to the amplitudes instead of the helicity-2 dominance assumed by {\it BABAR}, which may indicate a sizable portion of non-$q\bar q$ components in this state. Identifying the $X(3915)$ with the $X(3930)$ and abandoning the helicity-2 dominance for this tensor state are helpful for the further understandings of the properties of this state and also of the mysterious "$XYZ$" charmoniumlike resonances.

hep-ph↗

arXiv2015

Distinguishing cusp effects and near-threshold-pole effects

We make use of a unitarized coupled-channel model to analyze the mass distribution data of final states in production processes of $X(4260)$. By analyzing the analytical structures of the decay amplitudes, we find that the line shape of $Z_c(3900)$ signal is related to the combined effect of a pair of near-threshold "shadow" poles and the $(D\bar{D}^*)^\pm$ thresholds, in which the third-sheet pole might provide a dominant contribution. As all the coupled channels effects are tuning off, the trajectories of these two poles suggest that the $Z_c(3900)$ might originate from the attractive interaction of $(D^*\bar{D}^*)^\pm$ through a long-distance interaction, $e.g.$ $π$-exchange interaction, as a "deuteron-like" state. There is no nearby pole structure corresponding to the $Z_c(4025)$ signal in the $(D^*\bar{D}^*)^\pm$ mass distribution.

hep-ph↗

arXiv2013

Comprehending heavy charmonia and their decays by hadron loop effects

We present that including the hadron loop effects could help us to understand the spectrum of the heavier charmonium-like states and their decays simultaneously. The observed states could be represented by the poles on the complex energy plane. By coupling to the opened thresholds, the pole positions are shifted from the bare states predicted in the quenched potential model to the complex energy plane. The pole masses are generally pulled down from the bare masses and the open-charm decay widths are related to the imaginary parts of the pole positions. Moreover, we also analyze the pole trajectory of the $χ_{c1}(2P)$ state while the quark pair production rate from the vacuum changes in its uncertainty region, which indicates that the enigmatic X(3872) state may be regarded as a $1^{++}$ $c\bar{c}$ charmonium-dominated state dressed by the hadron loops as the others.

hep-ph↗

arXiv2011

Hadron loops effect on mass shifts of the charmed and charmed-strange spectra

The hadron loop effect is conjectured to be important in understanding discrepancies between the observed states in experiments and the theoretical expectations of non-relativistic potential model. We present that, in an easily operable procedure, the hadron loop effect could shift the poles downwards to reduce the differences and provide better descriptions of both the masses and the total widths, at least, of the radial quantum number $n=1$ charmed and charmed-strange states. The $1^1P_1-1^3P_1$ mixing phenomena could be naturally explained due to their couplings with common channels. The newly observed $D$ states are also addressed, but there are still some problems remaining unclear.

hep-ph↗

arXiv2011

The origin of light $0^{+}$ scalar resonances

We demonstrate how most of the light $J^{P}=0^{+}$ spectrum below $2.0\,\mathrm{GeV}$ and their decays can be consistently described by the unitarized quark model incorporating the chiral constraints of Adler zeros and taking SU(3) breaking effects into account. These resonances appear as poles in the complex $s$ plane in a unified picture as $q\bar{q}$ states strongly dressed by hadron loops. Through the large $N_c$ analysis, these resonances are found to naturally separate into two kinds: $σ, κ, f_0(980), a_0(980)$ are dynamically generated and run away from the real axis as $N_c$ increases, while the others move towards the $q\bar q $ seeds. In this picture, the line shape of $a_0(980)$ is produced by a broad pole below the $K\bar{K}$ threshold, and exhibits characteristics similar to the $σ$ and $κ$.

hep-ph↗