arXiv subjects

Qiang Zhao

Publications and source records attributed to Qiang Zhao.

At least 199 records · Page 11Linked to original sources

arXiv2009

Study of isospin violating $ϕ$ excitation in $e^+e^- \to ωπ^0$

We study the reaction $e^+ e^-\to ωπ^0$ in the vicinity of $ϕ$ mass region. The isospin-violating $ϕ$ excitation is accounted for by two major mechanisms. One is electromagnetic (EM) transition and the other is strong isospin violations. For the latter, we consider contributions from the intermediate hadronic meson loops and $ϕ$-$ρ^0$ mixing as the major mechanisms via the $t$ and s-channel transitions, respectively. By fitting the recent KLOE data, we succeed in constraining the model parameters and extracting the $ϕ\toωπ^0$ branching ratio. It shows that the branching ratio is sensitive to the $ϕ$ excitation line shape and background contributions. Some crucial insights into the correlation between isospin violation and Okubo-Zweig-Iizuka (OZI) rule evading transitions are also learned.

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arXiv2009

The $K^-p\to Σ^0π^0$ reaction at low energies in a chiral quark model

A chiral quark-model approach is extended to the study of the $\bar{K}N$ scattering at low energies. The process of $K^-p\to Σ^0π^0$ at $P_K\lesssim 800$ MeV/c (i.e. the center mass energy $W\lesssim 1.7$ GeV) is investigated. This approach is successful in describing the differential cross sections and total cross section with the roles of the low-lying $Λ$ resonances in $n=1$ shells clarified. The $Λ(1405)S_{01}$ dominates the reactions over the energy region considered here. Around $P_K\simeq 400$ MeV/c, the $Λ(1520)D_{03}$ is responsible for a strong resonant peak in the cross section. The $Λ(1670)S_{01}$ has obvious contributions around $P_K=750$ MeV/c, while the contribution of $Λ(1690)D_{03}$ is less important in this energy region. The non-resonant background contributions, i.e. $u$-channel and $t$-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.

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arXiv2009

Towards a dynamical understanding of the non-$D \bar D$ decay of $ψ(3770)$

We investigate the $ψ(3770)$ non-$D\bar{D}$ decays into $VP$, where $V$ and $P$ denote vector and pseudoscalar mesons, respectively, via OZI-rule-evading intermediate meson rescatterings in an effective Lagrangian theory. By identifying the leading meson loop transitions and constraining the model parameters with the available experimental data for $ψ(3770)\to J/ψη$, $ϕη$ and $ρπ$, we succeed in making a quantitative prediction for all $ψ(3770)\to VP$ with $BR_{VP}$ from 0.41% to 0.64%. It indicates that the OZI-rule-evading long-range interactions are still playing a role in $ψ(3770)$ strong decays, and could be a key towards a full understanding of the mysterious $ψ(3770)$ non-$D\bar{D}$ decay mechanism.

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arXiv2008

Further insights into the "$ρπ$ puzzle"

Based on a systematic investigation of $J/ψ(ψ^\prime)\to VP$, where $V$ and $P$ stand for light vector and pseudoscalar mesons, we identify the role played by the electromagnetic (EM) transitions and intermediate meson loop transitions, which are essential ingredients for understanding the $J/ψ$ and $ψ^\prime$ couplings to $VP$. We show that on the one hand, the EM transitions have relatively larger interferences in $ψ^\prime\to ρπ$ and $K^*\bar{K}+c.c.$ as explicitly shown by vector meson dominance (VMD). On the other hand, the strong decay of $ψ^\prime$ receives relatively larger destructive interferences from the intermediate meson loop transitions. By identifying these mechanisms in an overall study of $J/ψ(ψ^\prime)\to VP$, we provide a coherent understanding of the so-called "$ρπ$ puzzle".

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arXiv2008

Hadronic loop contributions to $J/ψ$ and $ψ^\prime$ radiative decays into $γη_c$ or $γη_c^\prime$

Intermediate hadronic meson loop contributions to $J/ψ$, $ψ^\prime \to γη_c$ ($γη_c^\prime$) are studied apart from the dominant M1 transitions in an effective Lagrangian approach. Due to the property of the unique antisymmetric tensor coupling in $V\to VP$, the hadronic loop transitions provide explicit corrections to the M1 transition amplitudes derived from the naive "quenched" $c\bar{c}$ transitions via the coupling form factors. This mechanism interfering with the M1 transition amplitudes naturally accounts for the deviations from the Godfrey-Isgur model predictions in $J/ψ$ and $ψ^\prime\to γη_c$. It also predicts a small branching ratio of $ψ^\prime\to γη_c^\prime$, which can be examined by experimental measurements at BES and CLEO-c.

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arXiv2008

Search for a promising tetraquark candidate $X(ud\bar{s}\bar{s})$ in $pn\to ΛΛX$

We propose to search for a tetraquark candidate $X(ud\bar{s}\bar{s})$ in $pn\to ΛΛX(ud\bar{s}\bar{s})\to ΛΛK^+K^0$ or $ΛΛKK^*$. The existence of tetraquark state $X(ud\bar{s}\bar{s})$ with $J^P=0^+$, $1^-$ or $1^+$ was predicted in the literature based on specific diquark effective degrees of freedom inside hadrons. In order to understand the underlying dynamics for exotic hadrons, a search for the tetraquark $X(ud\bar{s}\bar{s})$ is strongly recommended. The proposed reaction involves two $Λ$ production, of which the narrow widths make it a great advantage in the analysis of the final state missing mass spectrum. We make an estimate of the production rate of $X(ud\bar{s}\bar{s})$ in an effective Lagrangian theory and find that for $J^P=1^-$ the sample events of $\sim 2200 \ nb^{-1}$ will be able to identify $X(ud\bar{s}\bar{s})$ with five standard deviations at a width of 10 MeV to $K^+K^0$ near threshold. For $J^P=1^+$ with a width of 20 MeV to $KK^*$, the sample events of $\sim 130 nb^{-1}$ will be needed. Large production cross sections are expected in a kinematic region beyond the threshold. We emphasize the advantage of low background in this transition channel, and in the meantime caution the large uncertainties in the present estimate due to lack of knowledge about the $X(ud\bar{s}\bar{s})$ state. Implications for its heavy-flavored partners $qq\bar{c}\bar{c}$ and $qq\bar{b}\bar{b}$ are briefly discussed.

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arXiv2008

Possible contributions to $e^+e^- \to J/ψ+ η_c$ due to intermediate meson rescatterings

Inspired by the obvious discrepancies between experiment and non-relativistic QCD (NRQCD) studies of $e^+ e^-\to J/ψ+η_c$ at $\sqrt{s}\simeq 10.6$ GeV, we investigate contributions from intermediate meson loops as long-range interaction transitions to this process. The intermediate meson loops include $D\bar D(\bar D^\ast)$, $D\bar D^\ast(D {or} D^\ast)$, $D^\ast \bar D^\ast(D)$ and corresponding $D_s$ intermediate mesons. With the constraints from experimental data on the vertex couplings, we find that the intermediate meson loops account for $2.7\sim 6.7 fb$ of the cross sections within a reasonable range of cut-off energies of the factor parameter. We also investigate contributions from the absorptive part and find that it accounts for approximately $0.58\sim 1.38 fb$. These results imply that contributions from long-range interaction transitions may still play a role in such an energy region.

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arXiv2008

Strong decays of heavy-light mesons in a chiral quark model

We carry out a systematic study of the heavy-light meson strong decays in a chiral quark model. For the $S$-wave vectors ($D^*(2007)$, $D^{*\pm}(2010)$), $P$-wave scalars ($D^*_0(2400)$, $B^*_0(5730)$) and tensors ($D^*_2(2460)$, $D^*_{s2}(2573)$), we obtain results in good agreement with the experimental data. For the axial vectors $D_1(2420)$ and $D_1^\prime(2430)$, a state mixing scheme between $1^1P_1$ and $1^3P_1$ is favored with a mixing angle $ϕ\simeq-(55\pm 5)^\circ$, which is consistent with previous theoretical predictions. The same mixing scheme also applies to $D_{s1}(2460)$ and $D_{s1}(2536)$ that accounts for the narrow width of the $D_{s1}(2536)$ and its dominant decay into $D^*K$. For $B_1(5725)$ and $B_1^\prime(5732)$, such a mixing explains well the decay width of the former but leads to an even broader $B_1^\prime(5732)$. Predictions for the strange-bottom axial vectors are also made. For the undetermined meson $D^*(2640)$, we find that they fit in well the radially excited state $2^3S_1$ according to its decay mode. The newly observed $D^*_{sJ}(2860)$ strongly favors the $D$-wave excited state $1^3D_3$. For $D^*_{sJ}(2632)$ and $D^*_{sJ}(2690)$, we find they are difficult to fit in any $D_s$ excitations in that mass region, if the experimental data are accurate. Theoretical predictions for decay modes of those unobserved states as multiplets of 2S and 1D waves are also presented, which should be useful for further experimental search for those states.

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arXiv2008

Search for tetraquark candidate Z(4430) in meson photoproduction

We propose a search for the newly discovered tetraquark candidate Z(4430) in photoproduction. Based on the Belle results we show that if Z(4430) is a genuine resonance, its significantly large coupling to $ψ^\primeπ$ will cause it to stand out above the background in $γp\to Z^+(4430) n\to ψ^\prime π^+ n$. We consider the dependence of the cross section for the quantum numbers ($J^{P}=1^{-}$, $1^{+}$ or $0^{-}$).

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arXiv2008

Charmed baryon strong decays in a chiral quark model

Charmed baryon strong decays are studied in a chiral quark model. The data for the decays of $Λ^+_c(2593)$, $Λ^+_c(2625)$, $Σ^{++,+,0}_c$ and $Σ^{+,0}_c(2520)$, are accounted for successfully, which allows to fix the pseudoscalar-meson-quark couplings in an effective chiral Lagrangian. Extending this framework to analyze the strong decays of the newly observed charmed baryons, we classify that both $Λ_c(2880)$ and $Λ_c(2940)$ are $D$-wave states in the N=2 shell; $Λ_c(2880)$ could be $|Λ_c ^2 D_{λλ}{3/2}^+>$ and $Λ_c(2940)$ could be $|Λ_c ^2 D_{λλ}{5/2}^+>$. Our calculation also suggests that $Λ_c(2765)$ is very likely a $ρ$-mode $P$-wave excited state in the N=1 shell, and favors a $|Λ_c ^4P_ρ1/2^->$ configuration. The $Σ_c(2800)$ favors being a $|Σ_c ^2P_λ{1/2}^->$ state. But its being $|Σ^{++}_c ^4 P_λ{5/2}^->$ cannot be ruled out.

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arXiv2008

Decays of $J/ψ$ and $ψ^\prime$ into vector and pseudoscalar meson and the pseudoscalar glueball-$q\bar{q}$ mixing

We introduce a parametrization scheme for $J/ψ(ψ^\prime)\to VP$ where the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation (DOZI) can be parametrized by certain parameters with explicit physical interpretations. This scheme can be used to clarify the glueball-$q\bar{q}$ mixing within the pseudoscalar mesons. We also include the contributions from the electromagnetic (EM) decays of $J/ψ$ and $ψ^\prime$ via $J/ψ(ψ^\prime)\to γ^*\to VP$. Via study of the isospin violated channels, such as $J/ψ(ψ^\prime)\to ρη$, $ρη^\prime$, $ωπ^0$ and $ϕπ^0$, reasonable constraints on the EM decay contributions are obtained. With the up-to-date experimental data for $J/ψ(ψ^\prime)\to VP$, $J/ψ(ψ^\prime)\to γP$ and $P\to γγ$, etc, we arrive at a consistent description of the mentioned processes with a minimal set of parameters. As a consequence, we find that there exists an overall suppression of the $ψ^\prime\to 3g$ form factors, which sheds some light on the long-standing "$ρπ$ puzzle". By determining the glueball components inside the pseudoscalar $η$ and $η^\prime$ in three different glueball-$q\bar{q}$ mixing schemes, we deduce that the lowest pseudoscalar glueball, if exists, has rather small $q\bar{q}$ component, and it makes the $η(1405)$ a preferable candidate for $0^{-+}$ glueball.

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arXiv2007

Study of π^{-}p \to ηn at low energies in a chiral constituent quark model

A chiral quark model approach is extended to the study of the $πN$ scattering at low energies. The process of $π^{-}p \to ηn$ near threshold is investigated. The model is successful in describing the differential cross sections and total cross section near the $η$ production threshold. The roles of the resonances in $n\leq 2$ shells are clarified. Near threshold, the $S_{11}(1535)$ dominates the reactions, while the interferences from the $S_{11}(1650)$ turn out to be destructive around $W\lesssim 1.6$ GeV. The $D_{13}(1520)$ is crucial to give correct shapes of the differential cross sections. The nucleon pole term contributions are significant. The $P_{11}(1710)$ plays an important role around the c.m. energy $W=1.7$ GeV, it is crucial to produce an enhancement in the region of $W>1.6$ GeV as suggested by the data for total cross section. The $t$-channel is negligible in the reactions.

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arXiv2007

Selection rules and quark correlations in the $N^*$ resonance spectrum

A "$Λ$ selection rule" for $N^*$ resonances in the presence of QCD mixing effects is identified. Due to the QCD mixing, excitations of {\bf 20}-plets are possible in SU(6). We show that this selection rule is useful for classifying PDG states at N=2, and for clarifying whether strongly correlated diquarks survive for $L > 0$.

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arXiv2007

χ_{c0,2} decay into light meson pairs and its implication of the scalar meson structures

In light of the recent data from BES collaboration for $χ_{c0}\to VV$, $PP$ and $SS$, and from CLEO-c for $ηη$, $η^\primeη^\prime$ and $ηη^\prime$, we present a detailed analysis of the decays of heavy quarkonia into light meson pairs such as $χ_{c0,2}\to VV$, $PP$ and $SS$ in a recently proposed parametrization scheme. An overall agreement with the data is achieved in $χ_{c0,2}\to VV$ and $PP$, while in $χ_{c0}\to SS$ we find that a possible existence of glueball-$q\bar{q}$ mixings is correlated with the OZI-rule violations, which can be further examined at CLEO-c and BESIII in $χ_{c0}\to SS$ measurement.

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arXiv2007

Chiral constituent quark model study of the process $γp \to ηp$

A constituent quark model is developed for the reaction, allowing us to investigate all available data for differential cross sections as well as single polarization asymmetries (beam and target) by including {\it all} of the PDG, one to four star, nucleon resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $D_{15}$, $F_{15}$, $F_{17}$, $G_{17}$, $G_{19}$, $H_{19}$, $I_{1,11}$, and $K_{1,13}$). Issues related to the missing resonances are also briefly discussed by examining possible contributions from several new resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $ D_{15}$, and $H_{1,11}$).

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arXiv2007

Isospin violation in $ϕ, J/ψ, ψ^\prime \to ωπ^0$ via hadronic loops

In this work, we study the isospin-violating decay of $ϕ\to ωπ^0$ and quantify the electromagnetic (EM) transitions and intermediate meson exchanges as two major sources of the decay mechanisms. In the EM decays, the present datum status allows a good constraint on the EM decay form factor in the vector meson dominance (VMD) model, and it turns out that the EM transition can only account for about $1/4\sim 1/3$ of the branching ratio for $ϕ\to ωπ^0$. The intermediate meson exchanges, $K\bar{K}(K^*)$ (intermediate $K\bar{K}$ interaction via $K^*$ exchanges), $K\bar{K^*}(K)$ (intermediate $K\bar{K^*}$ rescattering via kaon exchanges), and $K\bar{K^*}(K^*)$ (intermediate $K\bar{K^*}$ rescattering via $K^*$ exchanges), which evade the naive Okubo-Zweig-Iizuka (OZI) rule, serve as another important contribution to the isospin violations. They are evaluated with effective Lagrangians where explicit constraints from experiment can be applied. Combining these three contributions, we obtain results in good agreement with the experimental data. This approach is also extended to $J/ψ(ψ^\prime)\to ωπ^0$, where we find contributions from the $K\bar{K}(K^*)$, $K\bar{K^*}(K)$ and $K\bar{K^*}(K^*)$ loops are negligibly small, and the isospin violation is likely to be dominated by the EM transition.

hep-ph↗

arXiv2007

$πN\to ηN$ process in a $χ$QM approach

A chiral quark model approach is used to investigate the $π^{-}p \to ηn$ process at low energies. The roles of the most relevant nucleon resonances in $n\leq 2$ shells are briefly discussed.

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arXiv2007

Possibility of measuring a0(980)-f0(980) mixing from J/psi -> phi a0

The a0(980)-f0(980) mixing intensity has been predicted to be in the range of 0.01 to 0.1 by various theoretical models, but lacking firm experimental observation. We examine the possibility of extracting the a0(980)-f0(980) mixing from J/psi -> phi f0 -> phi a0 reaction at upgraded Beijing Electron Positron Collider with BESIII detector. While the branching ratio of this process through the a0(980)-f0(980) mixing is expected to be about $O(10^{-6})$ similar to the estimated total amount from two background reactions J/psi -> gamma* -> phi a0 and J/psi -> K* K + c.c. -> phi a0, the peak width from the a0(980)-f0(980) mixing is about 8 MeV, much smaller than that from other mechanisms. With $10^9$ $J/ψ$ events at BESIII, the a0(980)-f0(980) mixing intensity is expected to be unambiguously and precisely measured.

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