Qian Wang

Forschungszentrum Jülich, Düren, North Rhine-Westphalia, Germany

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Publications (26)64.58 Total impact

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    Qian Wang · Xiao-Hai Liu · Qiang Zhao
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    ABSTRACT: We propose to study the pentaquark candidates of $P_c^+(4380)$ and $P_c^+(4450)$ in $J/\psi$ photoproduction and look for further experimental evidence for their nature. Since the photoproduction process does not satisfy the so-called "anomalous triangle singularity" condition their presence in $J/\psi$ photoproduction would conclude that they should be genuine states and provide further evidence for their existence.
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    Xiao-Hai Liu · Qian Wang · Qiang Zhao
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    ABSTRACT: We find that several thresholds can contribute to the enhancements of the newly observed heavy pentaquark candidates $P_c^+(4380)$ and $P_c^+(4450)$ via the anomalous triangle singularity (ATS) transitions in the specific kinematics of $\Lambda_b\to J/\psi K^- p$. Apart from the observed two peaks we find that another peaks around 4.5 GeV can also be produced by the ATS. We also show that the $\Sigma_c^{(*)}$ can be produced at leading order in $\Lambda_b$ decay. We find that this process is different from the triangle diagram and the threshold enhancement only appear as CUSP effects if there is no pole structure or the ATS involved. The threshold interaction associated by the presence of the ATS turns out to be a general phenomenon and plays a crucial role in the understanding of candidates for exotic states.
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    ABSTRACT: In order to test different models proposed for some states discovered recently in the charmonium mass range that do not fit into the pattern predicted by the conventional quark model, we derive predictions for the spectrum within the hadro-charmonium picture, the tetraquark picture as well as the hadronic molecular approach. We exploit heavy quark spin symmetry for the hadro-charmonium and hadronic molecule scenarios. The patterns that emerge from the different models turn out to be quite distinct. For example, only within the hadro-charmonium picture a pseudoscalar state emerges that is lighter than the $Y(4260)$. Possible discovery channels of these additional states are discussed.
  • Jean-Marc Richard · Qian Wang · Qiang Zhao
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    ABSTRACT: The status of the light hypernuclei is reviewed, and discussed with models based either on the Nijmegen-RIKEN baryon-baryon interaction or on recent studies using chiral effective field theory. The latter suggests a significantly shorter range for the ΛΛ interaction, and this favours the formation of a Borromean state made of two neutrons and two hyperons. Various corrections are discussed, in particular the coupling of NΛ to NΣ, or of ΛΛ to NΞ, and the role of tensor forces. The new nucleus 4ΛΛn = (n,n, Λ, Λ) could be produced in various reactions, in particular deuteron-deuteron scattering with the simultaneous production of two charged kaons, for which an estimate of the cross section is provided.
    Journal of Physics Conference Series 12/2014; 569(1). DOI:10.1088/1742-6596/569/1/012079
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    ABSTRACT: We demonstrate that the spectacular structures discovered recently in various experiments and named as $X$, $Y$ and $Z$ states cannot be purely kinematic effects. Their existence necessarily calls for nearby poles in the $S$--matrix and they therefore qualify as states. We propose a way to distinguishing kinematic cusp effects from genuine $S$--matrix poles: the kinematic threshold cusp cannot produce a narrow peak in the invariant mass distribution in the elastic channel in contrast with a genuine $S$--matrix pole.
    Physical Review D 11/2014; 91(5). DOI:10.1103/PhysRevD.91.051504 · 4.86 Impact Factor
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    ABSTRACT: Since its first observation in 2005, the vector charmonium $Y(4260)$ has turned out to be one of the prime candidates for an exotic state in the charmonium spectrum. It was recently proposed that the $Y(4260)$ should have a prominent ${D}_{1}\overline{D}+\mathrm{c}.\mathrm{c}.$ molecular component that is strongly correlated with the production of the charged ${Z}_{c}(3900)$. In this paper we demonstrate that the nontrivial cross section line shapes of ${e}^{+}{e}^{$-${}}$\rightarrow${}J/$\psi${}$\pi${}$\pi${}$ and ${h}_{c}$\pi${}$\pi${}$ can be naturally explained by the molecular scenario. As a consequence we find a significantly smaller mass for the $Y(4260)$ than previously studied. In the ${e}^{+}{e}^{$-${}}$\rightarrow${}\overline{D}{D}^{*}$\pi${}+\mathrm{c}.\mathrm{c}.$ process, with the inclusion of an additional $S$-wave ${\overline{D}}^{*}$\pi${}$ contribution constrained from data on the $D{\overline{D}}^{*}$ invariant mass distribution, we obtain a good agreement with the data of the angular distributions. We also predict an unusual line shape of $Y(4260)$ in this channel that may serve as a smoking gun for a predominantly molecular nature of $Y(4260)$. Improved measurements of these observables are therefore crucial for a better understanding of the structure of this famous resonance.
    Physical Review D 10/2014; 90(7). DOI:10.1103/PhysRevD.90.074039 · 4.86 Impact Factor
  • Source
    Gang Li · Xiao-Hai Liu · Qian Wang · Qiang Zhao
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    Jean-Marc Richard · Qian Wang · Qiang Zhao
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    ABSTRACT: The status of the light hypernuclei is reviewed, and discussed with models based either on the Nijmegen-RIKEN baryon--baryon interaction or on recent studies using chiral effective field theory. The latter suggests a significantly shorter range for the $\Lambda\Lambda$ interaction, and this favours the formation of a Borromean state made of two neutrons and two hyperons. Various corrections are discussed, in particular the coupling of $N\Lambda$ to $N\Sigma$, or of $\Lambda\Lambda$ to $N\Xi$, and the role of tensor forces. The new nucleus $(n,n,\Lambda,\Lambda)$ could be produced in various reactions, in particular deuteron--deuteron scattering with the simultaneous production of two charged kaons, for which an estimate of the cross section is provided.
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    Jean-Marc Richard · Qian Wang · Qiang Zhao
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    ABSTRACT: Our current knowledge of the baryon--baryon interaction suggests that the dineutron $(n,n)$ and its strange analogue $(\Lambda,n)$ are unstable. In contrast, the situation is more favourable for the strange three-body system $(n,n,\Lambda)$, and even better for the four-body system $T=(n,n,\Lambda,\Lambda)$ with strangeness $-2$, which is likely to be stable under spontaneous dissociation. This new nucleus could be produced and identified in central deuteron--deuteron collisions via reaction $d+d\to T+K^++K^+$, and the tetrabaryon $T$ could play an important role in catalysing the formation of a strange core in neutron stars.
    Physical Review C 04/2014; 91(1). DOI:10.1103/PhysRevC.91.014003 · 3.88 Impact Factor
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    Qian Wang
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    ABSTRACT: The charmed meson pair $(\frac{3}{2})^+$ and anti-$(\frac{1}{2})^-$, i.e. $D_1(2420)\bar D+c.c.$, $D_1(2420)\bar D^*+c.c.$, $D_2(2460)\bar D^*+c.c.$, can couple to states with vector quantum number $J^{PC}=1^{--}$ and exotic quantum number $J^{PC}=1^{-+}$ in a relative $S$ wave. Near threshold, the charmed meson pair may form hadronic molecules due to the strong $S$-wave coupling, and the mysterious vector state $Y(4260)$ could be such a state of the $D_1(2420)\bar D+c.c.$ molecule. This implies the possible existence of its exotic partner made of the same charmed mesons but with $J^{PC}=1^{-+}$. We evaluate the production rate of such exotic hadronic molecules and propose a direct experimental search for them in $e^+e^-$ annihilation. The confirmation of such exotic states in experiment will shed light on the spectrum in the heavy quark sector.
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    ABSTRACT: The isospin violation process $Y(4260) \to J/\psi \eta \pi^{0}$ is studied assuming that $Y(4260)$ is a $D_{1} \bar{D}+c.c.$ hadronic molecule. In association with the production of the $Z_c(3900)$, which is treated as a $D \bar{D}^{*}+c.c.$ hadronic molecule, this process can help us distinguish their molecular natures from other scenarios, since the incomplete cancellation between the charged and neutral--meson loops, which are prominent in the molecular picture only, produces a peak in the $e^+e^-\to Y(4260)\to J/\psi\eta\pi^0$ cross section at the $D_{1} \bar{D}+c.c.$ threshold and a very prominent peak in the $J/\psi \eta$ invariant mass spectrum in between the $D \bar{D}^{*}+c.c.$ thresholds; the latter being much narrower than the corresponding one in the isospin conserving channel, i.e. $J/\psi \pi^+ \pi^{-}$. The partial width of $Y(4260)\to J/\psi\eta\pi^0$ is about $4 \times 10^{-4}$ of that of $Y(4260)\to J/\psi\pi^+\pi^-$. The cross section of $e^+e^-\to Y(4260)\to J/\psi\eta\pi^0$ at the $D_{1} \bar{D}+c.c.$ threshold is about $0.05 \ \mathrm{pb}$ which is much larger than that produced by the nearby resonances. These features are the direct consequences of the assumed nature of these two states which might be accessible at the high-statistics experiments such as BESIII and LHCb.
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    Qian Wang · Christoph Hanhart · Qiang Zhao
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    ABSTRACT: We investigate in detail the "triangle singularity" regions of meson loops where the corresponding intermediate mesons are nearly-on-shell and have relatively small momenta, and the two heavy mesons strongly interact with each other in an $S$ wave. This $S$-wave interaction will make such kind of meson loops always enhanced and can explain experimental observations of threshold enhancements. We show that the production of the $Y(4260)$ and the recently observed $Z_c(3900)$ can be related to each other by this mechanism which will allow for a possible understanding of the nature of these threshold enhancements.
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    ABSTRACT: The vector charmonium Y(4260), since its first observation in 2005, has turned out to be a mysterious state in the charmonium spectrum. The recent observations of the charged charmonium state $Z_c(3900)$ by the BESIII and Belle Collaborations provide an opportunity for decoding its structure. It was recently proposed that the Y(4260) should have a prominent $D_1\bar{D}+c.c.$ molecular component that is strongly correlated with the production of the $Z_c(3900)$. In this Letter, we demonstrate that the nontrivial cross section line shapes of $e^+e^-\to J/\psi\pi\pi$ and $h_c\pi\pi$ can be naturally explained by the molecular scenario and an unusual line shape in $e^+e^-\to \bar{D}D^*\pi+c.c.$ is predicted as its signature.
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    Qian Wang · Christoph Hanhart · Qiang Zhao
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    ABSTRACT: The observation of $Z_c(3900)$ by the BESIII collaboration in the invariant mass spectrum of $J/\psi\pi^\pm$ in $e^+e^-\to J/\psi\pi^+\pi^-$ at the center of mass 4.260 GeV suggests the existence of a charged $\bar D D^*+D\bar D^*$ molecular state with $I(J^P)=1(1^+)$, which could be an isovector brother of the famous X(3872) and an analogue of $Z_b(10610)$ claimed by the Belle Collaboration. We demonstrate that this observation provides strong evidence that the mysterious Y(4260) is a $\bar{D}D_1(2420) +D\bar{D}_1(2420)$ molecular state. Especially, we show that the decay of this molecule naturally populates low momentum $\bar DD^*$ pairs and leads unavoidably to a cusp at the $\bar DD^*$ threshold. We discuss the signatures that distinguish such a $\bar DD^*$ cusp from the presence of a true resonance.
    Physical Review Letters 09/2013; 111(13):132003. DOI:10.1103/PhysRevLett.111.132003 · 7.51 Impact Factor
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    ABSTRACT: In this paper it is demonstrated that although the production of a (3/2)^+-(1/2)^- meson--anti-meson pair in e^+e^- collisions is suppressed in the heavy quark limit, it is not in conflict with such a scenario that the Y(4260) is dominated by a D_1\bar D+c.c. molecular component. Especially, we confront both the hadronic molecule and the hadro-charmonium interpretations of the Y(4260) with the experimental facts. We conclude that the the data presently available support the Y(4260) being dominantly a D_1\bar D+c.c. hadronic molecule while they challenge the hadro-charmonium interpretation.
    Physical Review D 09/2013; 89(3). DOI:10.1103/PhysRevD.89.034001 · 4.86 Impact Factor
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    Gang Li · Xiao-Hai Liu · Qian Wang · Qiang Zhao
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    ABSTRACT: We provide details of the study of ψ(3770) non-DD[over ¯] decays into VP, where V and P denote light vector meson and pseudoscalar meson, respectively. We find that the electromagnetic 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)→VP can be related to ψ(3686)→VP such that the parameters in our model can be constrained by comparing the different parts in ψ(3770)→VP to those in ψ(3686)→VP. Our quantitative results confirm the findings of Zhang et al. [Phys. Rev. Lett. 102, 172001 (2009)] that the OZI-rule-evading long-distance strong interaction via the intermediate meson loops plays an important role in ψ(3770) decays and could be a key towards a full understanding of the mysterious ψ(3770) non-DD[over ¯] decay mechanism.
    Physical review D: Particles and fields 07/2013; 88(1). DOI:10.1103/PhysRevD.88.014010 · 4.86 Impact Factor
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    ABSTRACT: 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.
    Physics Letters B 06/2013; 725(1). DOI:10.1016/j.physletb.2013.06.053 · 6.02 Impact Factor
  • Qian Wang · Christoph Hanhart · Qiang Zhao
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    ABSTRACT: We investigate in detail the role of heavy meson loops in the transition from $J^{PC}=1^{--}$ sources to candidates for QCD "exotics", such as $Z_c(3900)$, $Z_b(10610)$ and $Z_b'(10650)$. We demonstrate that, if a vector state strongly couples to a heavy meson pair in an $S$--wave and this system decays to another heavy meson pair (e.g. via pion emission), again in an $S$-wave, the pertinent diagrams get enhanced significantly, if the intermediate states are (near) on--shell and have small relative momenta. In a limited kinematic range this mechanism generates "singularity regions" that lead to the creation of a large number of low energy heavy meson pairs, providing an ideal environment for the formation of hadron-hadron bound states or resonances. For instance, we predict that the signals for $Z_b$ and $Z_b'$ should be a lot stronger in $\Upsilon(6S)$ decays due to this mechanism, if these states are indeed hadron-hadron resonances. The findings of this work should be valuable for deepening our understanding of the nature of the mentioned states.
    Physics Letters B 05/2013; DOI:10.1016/j.physletb.2013.06.049 · 6.02 Impact Factor
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    ABSTRACT: The decays of the $Z_b(10610)$ and the $Z_b(10650)$ to $\Upsilon(nS)\pi$, $h_b(mP)\pi$ and $\chi_{bJ}(mP)\gamma$ ($n=1,2,3$, $m=1,2$ and $J=0,1,2$) are investigated within a nonrelativistic effective field theory. It is argued that, while the decays to $\Upsilon(nS) \pi$ 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 $h_b(mP)\pi$ and $\chi_{bJ}(mP)\gamma$. In addition, the branching fractions for the neutral $Z_b$-states to $\chi_{bJ}\gamma$ are predicted to be of order $10^{-4}$--$10^{-3}$. This provides a fine test of the molecular nature in future high-luminosity experiments.
    Physical review D: Particles and fields 01/2013; 87(7). DOI:10.1103/PhysRevD.87.074006 · 4.86 Impact Factor
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    Qian Wang · Gang Li · Xiao-Hai Liu · Qiang Zhao
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    ABSTRACT: We identify open charm effects in a direct production process $e^+e^-\to J/\psi \pi^0$. 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 $\psi(3770)$ and $\psi(4040)$. 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 "$\rho\pi$ puzzle".

Publication Stats

158 Citations
64.58 Total Impact Points

Institutions

  • 2013
    • Forschungszentrum Jülich
      • Nuclear Physics Institute (IKP)
      Düren, North Rhine-Westphalia, Germany
  • 2012
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China
  • 2011–2012
    • Chinese Academy of Sciences
      • Institute of High Energy Physics
      Peping, Beijing, China