Qian Wang

Forschungszentrum Jülich, Düren, North Rhine-Westphalia, Germany

Are you Qian Wang?

Claim your profile

Publications (22)26.87 Total impact

  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    Qian Wang
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The observation of Z_{c}(3900) by the BESIII Collaboration in the invariant mass spectrum of J/ψπ^{±} in e^{+}e^{-}→J/ψπ^{+}π^{-} at the center of mass 4.260 GeV suggests the existence of a charged D[over ¯]D^{*}+DD[over ¯]^{*} 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 D[over ¯]D_{1}(2420)+DD[over ¯]_{1}(2420) molecular state. Especially, we show that the decay of this molecule naturally populates low momentum D[over ¯]D^{*} pairs and leads unavoidably to a cusp at the D[over ¯]D^{*} threshold. We discuss the signatures that distinguish such a D[over ¯]D^{*} cusp from the presence of a true resonance.
    Physical Review Letters 09/2013; 111(13):132003. DOI:10.1103/PhysRevLett.111.132003 · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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; DOI:10.1016/j.physletb.2013.06.053 · 6.02 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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".
  • Qian Wang, Xiao-Hai Liu, Qiang Zhao
    [Show abstract] [Hide abstract]
    ABSTRACT: We re-investigate the exclusive decays of ηcηc and ηc′ to a pair of light vector mesons, i.e. ηc(ηc′)→VV. The long-distance intermediate meson loop (IML) effects are evaluated as a non-perturbative mechanism in addition to the short-distance cc¯ annihilation contributions. We show that both processes can be reasonably well constrained with the help of the available experimental data. Since ηcηc and ηc′ are the spin-0 partners of J/ψJ/ψ and ψ′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”.
    Physics Letters B 05/2012; 711(5):364–370. DOI:10.1016/j.physletb.2012.04.022 · 6.02 Impact Factor
  • Source
    Qian Wang, Gang Li, Qiang Zhao
    [Show abstract] [Hide abstract]
    ABSTRACT: We evaluate the decay branching ratios of $\chi_{c1}\to PS$, 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.
    International Journal of Modern Physics A 02/2012; 27(23). DOI:10.1142/S0217751X12501357 · 1.09 Impact Factor
  • Source
    Qian Wang, Xiao-Hai Liu, Qiang Zhao
    [Show abstract] [Hide abstract]
    ABSTRACT: We re-investigate the exclusive decays of $\eta_c$ and $\eta_c^\prime$ to a pair of light vector mesons, i.e. $\eta_c (\eta_c')\to VV$. 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 $\eta_c$ and $\eta_c'$ are the spin-0 partners of $J/\psi$ and $\psi'$, respectively, our study is useful for gaining insights into the pQCD helicity selection rule violations in charmonium decays and the long-standing "$\rho\pi$ puzzle".
  • Source
    Qian Wang, Gang Li, Qiang Zhao
    [Show abstract] [Hide abstract]
    ABSTRACT: A detailed analysis of the open charm effects on the decays of $J/\psi(\psi^\prime)\to VP$ 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".
    Physical review D: Particles and fields 01/2012; 85(7). DOI:10.1103/PhysRevD.85.074015