arXiv subjects

Qiang Zhao

Publications and source records attributed to Qiang Zhao.

At least 163 records · Page 9Linked to original sources

arXiv2013

Further understanding of the non-$D\bar D$ decays of $ψ(3770)$

We provide details of the study of $ψ(3770)$ non-$D\bar D$ decays into $VP$, where $V$ and $P$ denote light vector meson and pseudoscalar meson, respectively. We find that the electromagnetic (EM) interaction plays little role in these processes, while the strong interaction dominates. The strong interaction can be separated into two parts, i.e. the short-distance part probing the wave function at origin and the long-distance part reflecting the soft gluon exchanged dynamics. The long-distance part is thus described by the intermediate charmed meson loops. We show that the transition of $ψ(3770)\to VP$ can be related to $ψ(3686)\to VP$ such that the parameters in our model can be constrained by comparing the different parts in $ψ(3770)\to VP$ to those in $ψ(3686)\to VP$. Our quantitative results confirm the findings of [Zhang {\it et al.}, Phys. Rev. Lett. 102, 172001 (2009)] that the OZI-rule-evading long-distance strong interaction via the IML plays an important role in $ψ(3770)$ 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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arXiv2013

Production of the X(3872) in charmonia radiative decays

We discuss the possibilities of producing the X(3872), which is assumed to be a D \bar D^* bound state, in radiative decays of charmonia. We argue that the ideal energy regions to observe the X(3872) associated with a photon in e^+e^- annihilations are around the Y(4260) mass and around 4.45 GeV, due to the presence of the S-wave D \bar D_1(2420) and D^* \bar D_1(2420) threshold, respectively. Especially, if the Y(4260) is dominantly a D \bar D_1 molecule and the X(3872) a D \bar D^* molecule, the radiative transition strength will be quite large.

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arXiv2013

Confirming the molecular nature of the $Z_b(10610)$ and the $Z_b(10650)$

The decays of the $Z_b(10610)$ and the $Z_b(10650)$ to $Υ(nS)π$, $h_b(mP)π$ and $χ_{bJ}(mP)γ$ ($n=1,2,3$, $m=1,2$ and $J=0,1,2$) are investigated within a nonrelativistic effective field theory. It is argued that, while the decays to $Υ(nS) π$ suffer from potentially large higher order corrections, the $P$-wave transitions of the $Z_b$ states offer the best possibility to confirm the nature of the $Z_b$ states as molecular states and to further study their properties. We give nontrivial and parameter-free predictions for the ratios of various partial widths for final states with $h_b(mP)π$ and $χ_{bJ}(mP)γ$. In addition, the branching fractions for the neutral $Z_b$-states to $χ_{bJ}γ$ are predicted to be of order $10^{-4}$--$10^{-3}$. This provides a fine test of the molecular nature in future high-luminosity experiments.

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arXiv2013

Understanding the property of $η(1405/1475)$ in the $J/ψ$ radiative decay

In this work we make a systematic analysis of the correlated processes $J/ψ\to γη(1440)/f_1(1420)$ with $η(1440)/f_1(1420)\to K\bar{K}π$, $ηππ$ and $3π$, where the role played by the so-called "triangle singularity mechanism" (TSM) is clarified. Our results agree well with the experimental data and suggest a small fraction of $f_1(1420)$ contributions in these processes. This study confirms our conclusion in [Phys. Rev. Lett. 108, 081803 (2012)] that the dynamic feature of the TSM can be recognized by the strong narrow peak observed in the $ππ$ invariant mass spectrum of $η(1440)\to 3π$ with anomalously large isospin violations. Nevertheless, we explicitly demonstrate that the TSM can produce obvious peak position shifts for the same $η(1440)$ or $f_1(1420)$ state in different decay channels. This is a strong evidence that the $η(1405)$ and $η(1475)$ are actually the same state, i.e. $η(1440)$. We also make an analysis of the radiative decays of $η(1440)\to γV$ ($V=ϕ$, $ρ^0$ or $ω$) which shows that such a one-state prescription seems not to have a conflict with the so-far existing experimental data. Our analysis may shed a light on the long-standing puzzling question on the nature of $η(1405)$ and $η(1475)$.

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arXiv2013

Hunting for a scalar glueball in exclusive B decays

Using flavor SU(3) symmetry for the light quarks validated by the available experimental data, we propose an intuitive way to hunt for a scalar glueball in B decays. In the presence of mixing between the glueball and ordinary scalar mesons, we explore the extraction of the mixing parameters. In particular, we discuss the implication from the recently available experimental data and show the sensitivities of B decays as a probe to the scalar structures. The future Super KEKB factory would allow access to establishing the mixing pattern among the scalars, and possibly allow one to disentangle the long-standing puzzle concerning the existence and mixings of the scalar glueball predicted by QCD.

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arXiv2012

$Z_b/Z_b^\prime \to Υπ$ and $h_b π$ decays in intermediate meson loops model

With the recent measurement of $Z_b(10610)$ and $Z_b(10650)\to B\bar{B}^*+c.c.$ and $B^*\bar{B}^*$, we investigate the transitions from the $Z_b(10610)$ and $Z_b(10650)$ to bottomonium states with emission of a pion via intermediate $B \ {B}^*$ meson loops. The experimental data can be reproduced in this approach with a commonly accepted range of values for the form factor cutoff parameter $α$. The $Υ(3S)π$ decay channels appear to experience obvious threshold effects which can be understood by the property of the loop integrals. By investigating the $α$-dependence of partial decay widths and ratios between different decay channels, we show that the intermediate $B \ {B}^*$ meson loops are crucial for driving the transitions of $Z_b/Z_b'\to Υ(nS)π$ with $n = 1, 2, 3$, and $h_b(mP)π$ with $m = 1$ and 2.

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arXiv2012

Study of the anomalous cross-section lineshape of e^+e^-\to D\bar D at ψ(3770) with an effective field theory

We study the anomalous cross-section lineshape of $e^+e^-\rightarrow D\bar D$ with an effective field theory. Near the threshold, most of the $D\bar D$ pairs are from the decay of $ψ(3770)$. Taking into account the fact that the nonresonance background is dominated by the $ψ(2S)$ transition, the produced $D\bar D$ pair can undergo final-state interactions before the pair is detected. We propose an effective field theory for the low-energy $D\bar D$ interactions to describe these final-state interactions and find that the anomalous lineshape of the $D\bar D$ cross section observed by the BESII collaboration can be well described.

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arXiv2012

The mass spectrum and strong decays of isoscalar tensor mesons

In this work, we present a systematic study of the observed isoscalar tensor $f_2$ states. With the detailed analysis of the mass spectrum and calculation of the $f_2$ two-body strong decays, we extract information of their underly structures, and try to categorize them into the conventional tensor meson family ($n^{3}P_{2}$ $(n=1,2,3,4)$ and $m^{3}F_{2}$ ($m=1,2$)). We also give predictions for other decay modes of these tensor mesons, which are useful for further experimental investigations.

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arXiv2012

Probing scalar meson structures in $χ_{c1}$ decays into pseudoscalar and scalar

We evaluate the decay branching ratios of $χ_{c1}\to PS$, in a quark model parametrization scheme, where $P$ and $S$ stand for pseudoscalar and scalar meson, respectively. An interesting feature of this decay process is that the $c\bar{c}$ annihilate via the pQCD hair-pin diagram is supposed to be dominant. Hence, this decay process should be sensitive to the quark components of the final-state light mesons, and would provide a great opportunity for testing the mixing relations among the scalar mesons, i.e. $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$, by tagging the final state pseudoscalar mesons.

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arXiv2012

The nature of X(3900) and recognition of open charm effects

We identify open charm effects in a direct production process $e^+e^-\to J/ψπ^0$. A unique feature of this process is that the $D\bar{D}^*+c.c.$ threshold is located at a relatively isolated energy region, i.e. $\sim 3.876 \ \mathrm{GeV}$, which is far away from the well-established charmonia $ψ(3770)$ and $ψ(4040)$. Therefore, the cross section line-shape of this reaction provides an opportunity for singling out the open charm effects. A model-independent narrow enhancement between the thresholds of $D^0\bar{D}^{*0}+c.c.$ and $D^+D^{*-}+c.c.$ is predicted. This study can also help understand the X(3900) enhancement recently observed by the Belle and BaBar Collaboration in $e^+e^-\to D\bar{D}+c.c.$ We also show that the open charm effects play a crucial role for our understanding of the long-standing "$ρπ$ puzzle".

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arXiv2012

The study of Ds1(2460) and Ds1(2536) mixing

In this proceeding, we report our recent study of the mixing mechanism between $D_{s1}(2460)$ and $D_{s1}(2536)$. On the basis of Godfrey-Isgur model, we consider the $D^*K$ hadron loop effect on the ${}^3P_1$ and ${}^1P_1$ $c\bar{s}$ states. We construct the propagator matrix of these two-state system, from which we can extract the poles as well as the mixing angles. Through this method, we simultaneously determine the masses, widths and mixing angle of these two physical states and the results agree well with the experimental measurement. Besides the mass shift, we also find that the hadron loop effects can cause a significant shift for the mixing angles from the value determined in the heavy quark symmetry limit.

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arXiv2012

Isospin violating decay of $ψ(3770)\rightarrow J/ψ+ π^0$

The strong-isospin violation in $ψ(3770)\rightarrow J/ψ+ π^0$ via intermediate $D$ meson loops is investigated in an effective Lagrangian approach. In this process, there is only one $D$-meson loop contributing to the absorptive part, and the uncertainties due to the introduction of form factors can be minimized. With the help of QCD spectral sum rules (QSSR), we extract the $J/ψDD^*$ form factor as an implement from the first principle of QCD. The $DD^*π^0$ form factor can be well determined from the experimental data for $D\rightarrowπlν$. The exploration of the dispersion relation suggests the dominance of the dispersive part via the intermediate $D$ meson loops even below the open charm threshold. This investigation could provide further insights into the puzzling question on the mechanisms for $ψ(3770)\to$ non-$D\bar{D}$ transitions.

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arXiv2012

Updated study of the $η_c$ and $η_c^\prime$ decays into light vector mesons

We re-investigate the exclusive decays of $η_c$ and $η_c^\prime$ to a pair of light vector mesons, i.e. $η_c (η_c')\to VV$. The long-distance intermediate meson loop (IML) effects are evaluated as a non-perturbative mechanism in addition to the short-distance $c\bar{c}$ annihilation contributions. We show that both processes can be reasonably well constrained with the help of the available experimental data. Since $η_c$ and $η_c'$ are the spin-0 partners of $J/ψ$ and $ψ'$, respectively, our study is useful for gaining insights into the pQCD helicity selection rule violations in charmonium decays and the long-standing "$ρπ$ puzzle".

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arXiv2012

Novel insights into the $γγ^*\to π^0$ transition form factor

BaBar's observation of significant deviations of the pion transition form factor (TFF) from the asymptotic expectation with $Q^2>9$ GeV$^2$ has brought a serious crisis to a fundamental picture established for such a simplest $q\bar{q}$ system by perturbative QCD, i.e. the dominance of collinear factorization at high momentum transfers for the pion TFF. We show that non-factorizable contributions due to open flavors in $γγ^*\toπ^0$ could be an important source that contaminates the pQCD asymptotic limit and causes such deviations with $Q^2>9$ GeV$^2$. Within an effective Lagrangian approach, the non-factorizable amplitudes can be related to intermediate hadron loops, i.e. $K^{(*)}$ and $D^{(*)}$ etc, and their corrections to the $π^0$ and $η$ TFFs can be estimated.

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arXiv2012

Open charm effects in the explanation of the long-standing "$ρπ$ puzzle"

A detailed analysis of the open charm effects on the decays of $J/ψ(ψ^\prime)\to VP$ is presented, where $V$ stands for light vector meson and $P$ for light pseudoscalar meson. These are the channels that the so-called "12% rule" of perturbative QCD (pQCD) is obviously violated. Nevertheless, they are also the channels that violate the pQCD helicity selection rule (HSR) at leading order. In this work, we put constraints on the electromagnetic (EM) contribution, short-distance contribution from the $c\bar{c}$ annihilation at the wavefunction origin, and long-distance contribution from the open charm threshold effects on these two decays. We show that interferences among these amplitudes, in particular, the destructive interferences between the short-distance and long-distance strong amplitudes play a key role to evade the HSR and cause the significant deviations from the pQCD expected "12% rule".

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arXiv2012

The puzzle of anomalously large isospin violations in $η(1405/1475)\to 3π$

The BES-III Collaboration recently report the observation of anomalously large isospin violations in $J/ψ\to γη(1405/1475) \to γπ^0 f_0(980)\to γ+3π$, where the $f_0(980)$ in the $ππ$ invariant mass spectrum appears to be much narrower ($\sim$ 10 MeV) than the peak width ($\sim$50 MeV) measured in other processes. We show that a mechanism, named as triangle singularity (TS), can produce a narrow enhancement between the charged and neutral $K\bar{K}$ thresholds, i.e., $2m_{K^\pm}\sim 2m_{K^0}$. It can also lead to different invariant mass spectra for $η(1405/1475)\to a_0(980)π$ and $K\bar{K}^*+c.c.$, which can possibly explain the long-standing puzzle about the need for two close states $η(1405)$ and $η(1475)$ in $ηππ$ and $K\bar{K}π$, respectively. The TS could be a key to our understanding of the nature of $η(1405/1475)$ and advance our knowledge about the mixing between $a_0(980)$ and $f_0(980)$.

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arXiv2012

The mixing of $D_{s1}(2460)$ and $D_{s1}(2536)$

The mixing mechanism of axial-vectors $D_{s1}(2460)$ and $D_{s1}(2536)$ is studied via intermediate hadron loops, e.g. $D^* K$, to which both states have strong couplings. By constructing the two-state mixing propagator matrix that respects the unitarity constraint and calculating the vertex coupling form factors in a chiral quark model, we can extract the masses, widths and mixing angles of the physical states. Two poles can be identified in the propagator matrix. One is at $\sqrt{s}=2454.5 \ \textrm{MeV}$ corresponding to $D_{s1}(2460)$ and the other at $\sqrt{s}=(2544.9-1.0i) \ \textrm{MeV}$ corresponding to $D_{s1}(2536)$. For $D_{s1}(2460)$, a large mixing angle $θ=47.5^\circ$ between ${}^3P_1$ and ${}^1P_1$ is obtained. It is driven by the real part of the mixing matrix element and corresponds to $θ'=12.3^\circ$ between the $j=1/2$ and $j=3/2$ state mixing in the heavy quark limit. For $D_{s1}(2536)$, a mixing angle $θ=39.7^\circ$ which corresponds to $θ'=4.4^\circ$ in the heavy quark limit is found. An additional phase angle $ϕ=-6.9^\circ \sim 6.9^\circ$ is needed at the pole mass of $D_{s1}(2536)$ since the mixing matrix elements are complex numbers. Both the real and imaginary part are found important for the large mixing angle. We show that the new experimental data from BaBar provide a strong constraint on the mixing angle at the mass of $D_{s1}(2536)$, from which two values can be extracted, i.e. $θ_1=32.1^\circ$ or $θ_2=38.4^\circ$. Our study agrees well with the latter one. Detailed analysis of the mass shift procedure due to the coupled channel effects is also presented.

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arXiv2012

$η_c$ mixing effects on charmonium and $B$ meson decays

We include the $η_c$ meson into the $η$-$η'$-$G$ mixing formalism constructed in our previous work, where $G$ represents the pseudoscalar gluball. The mixing angles in this tetramixing matrix are constrained by theoretical and experimental implications from relevant hadronic processes. Especially, the angle between $η_c$ and $G$ is found to be about $11^\circ$ from the measured decay widths of the $η_c$ meson. The pseudoscalar glueball mass $m_G$, the pseudoscalar densities $m_{qq,ss,cc}$ and the U(1) anomaly matrix elements associated with the mixed states are solved from the anomalous Ward identities. The solution $m_G\approx 1.4$ GeV obtained from the $η$-$η'$-$G$ mixing is confirmed, while $m_{qq}$ grows to above the pion mass, and thus increases perturbative QCD predictions for the branching ratios $Br(B\toη'K)$. We then analyze the $η_c$-mixing effects on charmonium magnetic dipole transitions, and on the $B\toη^{(\prime)}K_S$ branching ratios and CP asymmetries, which further improve the consistency between theoretical predictions and data. A predominant observation is that the $η_c$ mixing enhances the perturbative QCD predictions for $Br(B\toη'K)$ by 18%, but does not alter those for $Br(B\toηK)$. The puzzle due to the large $Br(B\toη'K)$ data is then resolved.

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