Showing papers by "Xiang Liu published in 2015"

Identifying exotic hidden-charm pentaquarks

Abstract: The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states P_{c}(4380) and P_{c}(4450). These two hidden-charm states are interpreted as the loosely bound Σ_{c}(2455)D^{*} and Σ_{c}^{*}(2520)D^{*} molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of P_{c}(4450) is much narrower than that of P_{c}(4380). The discovery of the new resonances P_{c}(4380) and P_{c}(4450), indeed, opens a new page for hadron physics. The partners of P_{c}(4380) and P_{c}(4450) should be pursued in future experiments.

Towards exotic hidden-charm pentaquarks in QCD

Abstract: Inspired by P(c)(4380) and P(c)(4450) recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anticharmed meson and a charmed baryon. Our results suggest that P(c)(4380) and P(c)(4450) have quantum numbers J(P)=3/2(-) and 5/2(+), respectively. Furthermore, two extra hidden-charm pentaqurks with configurations DΣ(c)(*) and D(*)Σ(c)(*) are predicted, which have spin-parity quantum numbers J(P)=3/2(-) and J(P)=5/2(+), respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of P(c)(4380) and P(c)(4450) are especially accessible at future experiments like LHCb and BelleII.

P-wave charmed baryons from QCD sum rules

Abstract: We study the $P$-wave charmed baryons using the method of QCD sum rule in the framework of heavy quark effective theory. We consider systematically all possible baryon currents with a derivative for internal $\ensuremath{\rho}$- and $\ensuremath{\lambda}$-mode excitations. We have found a good working window for the currents corresponding to the $\ensuremath{\rho}$-mode excitations for ${\mathrm{\ensuremath{\Lambda}}}_{c}(2595)$, ${\mathrm{\ensuremath{\Lambda}}}_{c}(2625)$, ${\mathrm{\ensuremath{\Xi}}}_{c}(2790)$, and ${\mathrm{\ensuremath{\Xi}}}_{c}(2815)$ that complete two $SU(3)$ ${\overline{\mathbf{3}}}_{F}$ multiplets of ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$, while the currents corresponding to the $\ensuremath{\lambda}$-mode excitations seem also consistent with the data. Our results also suggest that there are two ${\mathrm{\ensuremath{\Sigma}}}_{c}(2800)$ states of ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$ whose mass splitting is $14\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{MeV}$, and two ${\mathrm{\ensuremath{\Xi}}}_{c}(2980)$ states whose mass splitting is $12\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{MeV}$. They have two ${\mathrm{\ensuremath{\Omega}}}_{c}$ partners of ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$, whose masses are around $3.25\ifmmode\pm\else\textpm\fi{}0.20\text{ }\text{ }\mathrm{GeV}$ with mass splitting $10\ifmmode\pm\else\textpm\fi{}6\text{ }\text{ }\mathrm{MeV}$. All of them together complete two $SU(3)$ ${\mathbf{6}}_{F}$ multiplets of ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$. They may also have ${J}^{P}=5/{2}^{\ensuremath{-}}$ partners. ${\mathrm{\ensuremath{\Xi}}}_{c}(3080)$ may be one of them, and the other two are ${\mathrm{\ensuremath{\Sigma}}}_{c}(5/{2}^{\ensuremath{-}})$ and ${\mathrm{\ensuremath{\Omega}}}_{c}(5/{2}^{\ensuremath{-}})$, whose masses are $85\ifmmode\pm\else\textpm\fi{}23\text{ }\text{ }\mathrm{MeV}$ and $50\ifmmode\pm\else\textpm\fi{}27\text{ }\text{ }\mathrm{MeV}$ larger.

Charmed-strange mesons revisited: mass spectra and strong decays

Abstract: Inspired by the present experimental status of charmed-strange mesons, we perform a systematic study of the charmed-strange meson family in which we calculate the mass spectra of the charmed-strange meson family by taking a screening effect into account in the Godfrey-Isgur model and investigate the corresponding strong decays via the quark pair creation model. These phenomenological analyses of charmed-strange mesons not only shed light on the features of the observed charmed-strange states, but also provide important information on future experimental search for the missing higher radial and orbital excitations in the charmed-strange meson family, which will be a valuable task in LHCb, the forthcoming Belle II, and PANDA.

Higher radial and orbital excitations in the charmed meson family

Abstract: Using abundant experimental information about charmed mesons together with recent research, we systematically study higher radial and orbital excitations in the charmed meson family by analyzing the mass spectrum and by calculating their Okubo-Zweig-Iizuka-allowed two-body decay behaviors This phenomenological analysis reveals underlying properties of the newly observed charmed states $D(2550)$, ${D}^{*}(2600)$, ${D}^{*}(2760)$, $D(2750)$, ${D}_{J}(2580)$, ${D}_{J}^{*}(2650)$, ${D}_{J}^{*}(2760)$, ${D}_{J}(2740)$, ${D}_{J}(3000)$, and ${D}_{J}^{*}(3000)$ to provide valuable information about the charmed mesons still missing in experiments

QCD sum rule calculation for P-wave bottom baryons

Abstract: We study the P-wave bottom baryons using the method of QCD sum rule and heavy quark effective theory. Our results suggest that Lambda(b) (5912)(0) and Lambda(b) (5920)(0) can be well described by the baryon doublet [(3) over bar (F), 1, 1, rho], and they belong to the SU(3) IF multiplets of J(P) = 1/2(-) and 3/2(-). Their SU(3) flavor partners, Xi(b)(1/2(-)) and Xi(b) (3/2(-)), have masses 6.06 +/- 0.13 GeV and 6.07 +/- 0.13 GeV, respectively, with mass splitting 9 * 4 McV. The results obtained using baryon doublet [(3) over bar (F), 1, 0, lambda] are similar and also consistent with the experimental data. We also study the SU(3) 6(F) multiplets by using the baryon multiplets [6(F), 0, 1, lambda], [6(F), 1, 0, rho] and [6(F), 2, 1, lambda], and our results suggest that the P-wave bottom baryons Sigma(b), Xi(b)' and Omega(b) have (averaged) masses of about 6.0 GeV, 6.2 GeV and 6.4 GeV, respectively.

Masses and axial currents of the doubly charmed baryons

Abstract: The chiral dynamics of the doubly heavy baryons is solely governed by the light quark. In this paper, we have derived the chiral corrections to the mass of the doubly heavy baryons up to ${\mathrm{N}}^{3}\mathrm{LO}$. The mass splitting of ${\mathrm{\ensuremath{\Xi}}}_{cc}$ and ${\mathrm{\ensuremath{\Omega}}}_{cc}$ at the ${\mathrm{N}}^{2}\mathrm{LO}$ depends on one unknown low energy constant ${c}_{7}$. By fitting the lattice masses of ${\mathrm{\ensuremath{\Xi}}}_{cc}(3520)$, we estimate the mass of ${\mathrm{\ensuremath{\Omega}}}_{cc}$ to be around 3.726 GeV. Moreover, we have also performed a systematical analysis of the chiral corrections to the axial currents and axial charges of the doubly heavy baryons. The chiral structure and analytical expressions will be very useful to the chiral extrapolations of the future lattice QCD simulations of the doubly heavy baryons.

A QCD sum rule calculation for P-wave bottom baryons

Abstract: We study the P-wave bottom baryons using the method of QCD sum rule and heavy quark effective theory. Our results suggest thatb(5912) 0 andb(5920) 0 can be well described by the baryon doublet (¯F,1,1,�), and they belong to the SU(3) ¯F multiplets of J P = 1/2 − and 3/2 − . Their SU(3) flavor partners, �b(1/2 − ) andb(3/2 − ), have masses 6.06 ± 0.13 GeV and 6.07 ± 0.13 GeV, respectively, with mass splitting 9 ± 4 MeV. The results obtained using baryon doublet (¯F,1,0,�) are similar and also consistent with the experimental data. We also study the SU(3) 6F multiplets by using the baryon multiplets (6F,0,1,�), (6F,1,0,�) and (6F,2,1,�), and our results suggest that the P-wave bottom baryonsb, � ' and b have (averaged) masses about 6.0 GeV, 6.2 GeV and 6.4 GeV, respectively.

Light axial vector mesons

Abstract: Inspired by the abundant experimental observation of axial-vector states, we study whether the observed axial-vector states can be categorized into the conventional axial-vector meson family. In this paper we carry out an analysis based on the mass spectra and two-body Okubo-Zweig-Iizuka-allowed decays. Besides testing the possible axial-vector meson assignments, we also predict abundant information for their decays and the properties of some missing axial-vector mesons, which are valuable for further experimental exploration of the observed and predicted axial-vector mesons.

Combined study of 2 S and 1 D open-charm mesons with natural spin-parity

Abstract: In this paper, we perform a combined study of $2S$ and $1D$ open-charm mesons with natural spin-parity. Our results indicate that ${D}_{1}^{*}(2600)/{D}_{s1}^{*}(2700)$ and ${D}_{1}^{*}(2760)/{D}_{s1}^{*}(2860)$ are predominantly the $2^{3}{S}_{1}$ and $1^{3}{D}_{1}$ charmed/charmed-strange mesons, respectively, while ${D}_{3}^{*}(2760)/{D}_{s3}^{*}(2860)$ can be regarded as the $1^{3}{D}_{3}$ charmed/charmed-strange mesons. In addition, some typical ratios of partial widths of the discussed natural states are predicted, by which future experiments can test these assignments, especially for the $2S\text{\ensuremath{-}}1D$ mixing scheme existing in ${D}_{1}^{*}(2600)/{D}_{1}^{*}(2760)$ and ${D}_{s1}^{*}(2700)/{D}_{s1}^{*}(2860)$.

Strong decays of the $XYZ$ states

Abstract: Through the spin rearrangement scheme in the heavy quark limit, we have performed a comprehensive investigation of the decay pattern and production mechanism of the hidden beauty dimeson states, which are either composed of a $P$-wave bottom meson and an $S$-wave bottom meson or two $S$-wave bottom mesons. We further extend the corresponding formula to discuss the decay behavior of some charmonium-like states by combining the experimental information with our numerical results. The typical ratios presented in this work can be measured by future experiments like BESIII, Belle, LHCb and the forthcoming BelleII, which shall provide important clues to the inner structures of the exotic states.

Pseudotensor meson family

Abstract: The pseudoscalar tensor states, ${\ensuremath{\pi}}_{2}$, ${\ensuremath{\eta}}_{2}$, and ${K}_{2}$, are systematically studied through the Okubo-Zweig-Iizuka- allowed two-body strong decays, including both the observed states reported by the Particle Data Group and the predicted states. Phenomenological analysis combined with the experimental data not only can test the assignments to these discussed states, but it can also predict more abundant information on their partial decay widths, which is helpful in the experimental study of these observed and predicted pseudotensor states.

Observation of $e^+e^-\to \chi_{c0}\omega$ and missing higher charmonium $\psi(4S)$

Abstract: Stimulated by the recent BESIII observation of a new resonance in $e^+ e^- \to \omega \chi_{c0}$ and by the fact that this state is consistent with our predicted $\psi(4S)$, in this work we estimate the meson loop contribution to $\psi(4S) \to \omega \chi_{c0}$. The evaluation indicates that our theoretical estimate can overlap with the experimental data in a reasonable parameter range. This fact shows that introduction of the missing higher charmonium $\psi(4S)$ provides a possible explanation to the recent BESIII observation. The upper limit of a branching ratio of $\psi(4S) \to \eta J/\psi$ is also predicted as $1.9 \times 10^{-3}$, which can be further tested by BESIII, Belle and forthcoming BelleII.

a 1 ( 1420 ) resonance as a tetraquark state and its isospin partner

Abstract: We systematically construct tetraquark currents of ${I}^{\mathrm{G}}{J}^{\mathrm{PC}}={1}^{\ensuremath{-}}{1}^{++}$ and classify them into types $\mathbf{A}$ (antisymmetric), $\mathbf{S}$ (symmetric) and $\mathbf{M}$ (mixed), based on flavor symmetries of diquarks and antidiquarks composing the tetraquark currents. We use tetraquark currents of type $\mathbf{M}$ to perform QCD sum rule analyses, and find a tetraquark current ${\ensuremath{\eta}}_{5\ensuremath{\mu}}^{M}$ with quark content $qs\overline{q}\overline{s}$ ($q=u$ or $d$) leading to a mass of $1.44\ifmmode\pm\else\textpm\fi{}0.08\text{ }\text{ }\mathrm{GeV}$ consistent with the ${a}_{1}(1420)$ state recently observed by the COMPASS Collaboration. Our results support tetraquark explanations for both ${a}_{1}(1420)$ and ${f}_{1}(1420)$, assuming that they are isospin partners. We also study their possible decay patterns. As tetraquark candidates, the possible decay modes of ${a}_{1}(1420)$ are $S$-wave ${a}_{1}(1420)\ensuremath{\rightarrow}{K}^{*}(892)K$ and $P$-wave ${a}_{1}(1420)\ensuremath{\rightarrow}{f}_{0}(980)\ensuremath{\pi}$, while the possible decay patterns of ${f}_{1}(1420)$ are $S$-wave ${f}_{1}(1420)\ensuremath{\rightarrow}{K}^{*}(892)K$ and $P$-wave ${f}_{1}(1420)\ensuremath{\rightarrow}{a}_{0}(980)\ensuremath{\pi}$. We speculate that ${a}_{1}(1420)$ is partly responsible for the large isospin violation in the $\ensuremath{\eta}(1405)\ensuremath{\rightarrow}{f}_{0}(980){\ensuremath{\pi}}_{0}$ decay mode, which is reported by BESIII Collaboration in the $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}3\ensuremath{\pi}$ process.

F-wave heavy-light meson spectroscopy in QCD sum rules and heavy quark effective theory

Abstract: We study the F-wave (c) over bars heavy meson doublets (2(+), 3(+)) and (3(+), 4(+)). They have large orbital excitations L = 3, and may be good challenges (tests) for theoretical studies. To study them we use the method of QCD sum rule in the framework of heavy quark effective theory. Their masses are predicted to be m((2+,3+)) = (3.45 +/- 0.25, 3.50 +/- 0.26) GeV and m((3+,4+)) = (3.20 +/- 0.22, 3.26 +/- 0.23) GeV, with mass splittings Delta m((2+,3+)) = m(3+) - m(2+) = 0.046 +/- 0.030 GeV and Delta m((3+,4+)) = 0.053 +/- 0.044 GeV, respectively. We note that this is a pioneering work and these results are provisional.

\(D_{s1}^*(2860)\) and \(D_{s3}^*(2860)\) : candidates for \(1D\) charmed-strange mesons

Abstract: Newly observed two charmed-strange resonances, $$D_{s1}^*(2860)$$ and $$D_{s3}^*(2860)$$ , are investigated by calculating their Okubo–Zweig–Iizuka-allowed strong decays, which shows that they are suitable candidates for the $$1^3D_1$$ and $$1^3D_3$$ states in the charmed-strange meson family. Our study also predicts other main decay modes of $$D_{s1}^*(2860)$$ and $$D_{s3}^*(2860)$$ , which can be accessible at the future experiment. In addition, the decay behaviors of the spin partners of $$D_{s1}^*(2860)$$ and $$D_{s3}^*(2860)$$ , i.e., $$1D(2^-)$$ and $$1D^\prime (2^-)$$ , are predicted in this work, which are still missing at present. The experimental search for the missing $$1D(2^-)$$ and $$1D^\prime (2^-)$$ charmed-strange mesons is an intriguing and challenging task for further experiments.

High-spin mesons below 3 GeV

Abstract: In this work, we study the high-spin states with masses below 3 GeV observed in experiments, and we perform an analysis of mass spectrum and an investigation of strong decay behaviors of the high-spin states. Comparing our results with the experimental data, we can reveal the underlying properties of these high-spin states; more importantly, we also predict their abundant decay features, which can provide valuable information for experimental exploration of these high-spin states.

Hidden-charm decays of $X(3915)$ and $Z(3930)$ as the P-wave charmonia

Abstract: c2 (2P) assignments to X (3915) and Z (3930), respectively. The results show that the decay width of Z (3930) → J/ψω is at least one order smaller than that of X (3915) → J/ψω .T his observation explains why only one structure, X (3915), has been observed in the J/ψω invariant mass spectrum for the process γγ → J/ψω.

Using $X(3823)\to J/\psi\pi^+\pi^-$ to identify coupled-channel effects

Abstract: Very recently, the Belle and BESIII experiments observed a new charmonium-like state $X(3823)$, which is a good candidate for the $D$-wave charmonium $\psi(1^3D_2)$. Because the $X(3823)$ is just near the $D\bar{D}^*$ threshold, the decay $X(3823)\to J/\psi\pi^+\pi^-$ can be a golden channel to test the significance of coupled-channel effects. In this work, this decay is considered including both the hidden-charm dipion and the usual quantum chromodynamics multipole expansion (QCDME) contributions. The partial decay width, the dipion invariant mass spectrum distribution $\mathrm{d}\Gamma[X(3823)\to J/\psi\pi^+\pi^-]/\mathrm{d}m_{\pi^+\pi^-}$, and the corresponding $\mathrm{d}\Gamma[X(3823)\to J/\psi\pi^+\pi^-]/\mathrm{d}\cos\theta$ distribution are computed. Many parameters are determined from existing experimental data, so the results depend mainly only on one unknown phase between the QCDME and hidden-charm dipion amplitudes.

Predictions of the hidden-charm molecular states with four-quark component

Abstract: In this work, we study the $T\bar{T}$-type molecular systems systematically via one pion exchange model, where $T$ denotes the narrow $J^P=1^+$ $D_1$ meson or $2^+$ $D_2^*$ meson and $\bar{T}$ is its antiparticle. With the effective potentials, we try to find the bound state solutions of the corresponding systems, which provide crucial information of whether there exist the $T\bar{T}$-type molecular states. According to our analysis, we predict some $T\bar{T}$-type molecular states which may be accessible at future experiments like LHCb and forthcoming BelleII.

Prediction of isoscalar charmoniumlike structures in the hidden-charm di-eta decays of higher charmonia

Abstract: Considering the situation that a single chiral particle, η is initially emitted, we study the hidden-charm di-eta decays of the charmoniumlike state and the predicted charmonium , i.e., through the inetermediates and/or , and answer the important question of whether there exist isoscalar charmoniumlike structures in the and/or channels. Our results predict that there will be enhancement structures near , and thresholds for and near , and thresholds for in the distributions of , respectively. These peaks are accessible in future experiments, especially BESIII, Belle, BaBar, and the forthcoming BelleII.

Implication the observed $\psi(3770)\to p\bar{p}\pi^0$ for studying the $p\bar{p}\to \psi(3770)\pi^0$ process

Abstract: We study the charmonium $p \bar{p} \to \psi(3770) \pi^0$ reaction using effective lagrangian approach where the contributions from well established $N^*$ states are considered, and all parameters are fixed in the process of $e^+e^- \to p \bar{p}\pi^0$ at center of mass energy $\sqrt{s} = 3.773$ GeV. The experimental data on the line shape of the mass distribution of the $e^+e^- \to p\bar{p}\pi^0$ can be well reproduced. Based on the studying of $e^+e^- \to p \bar{p}\pi^0$, the total and differential cross sections of the $p \bar{p} \to \psi(3770) \pi^0$ reaction are predicted. At the same time we evaluated also the cross sections of the $p \bar{p} \to \psi(3686) \pi^0$ reaction. It is shown that the contribution of nucleon pole to this reaction is largest close to the reaction threshold. However, the interference between nucleon pole and the other nucleon resonance can still change the angle distributions significantly. Those theoretical results may be test by the future experiments at $\overline{\mbox{P}}$ANDA.

Exploration of charmed pentaquarks

Abstract: In this work, we explore the charmed pentaquarks, where the relativistic five-quark equations are obtained by the dispersion relation technique. By solving these equations with the method based on the extraction of the leading singularities of the amplitudes, we predict the mass spectrum of charmed pentaquarks with $J^P=1/2^{\pm}$ and $3/2^{\pm}$, which is valuable to further experimental study of charmed pentaquark.

Charged charmonium-like structures and the initial single chiral particle emission mechanism

Abstract: This paper summarizes what we have done so far to explain charged charmonium/bottomonium-like structures using a hadronic triangle diagram which we call the initial single chiral particle emission mechanism. We discuss processes like $A\to A'+P+P'$ in which two chiral particles $P$ and $P'$ are emitted from $A$. In the intermediate we consider a hadronic one-loop diagram in which $D^{(*)}/D_s^{(*)}/B^{(*)}/B_s^{(*)}$ are included to explain some enhancements experimentally observed. Using this mechanism we explain some of the exotic enhancements and predict a couple of enhancement structures.