Hidden-charm States Research Articles

Light- and heavy-quark symmetries and the Y(4230) , Y(4360) , Y(4500) , Y(4620) , and X(4630) resonances

The heavy hadron spectrum is constrained by symmetries, of which two of the most important ones are heavy-quark spin and SU(3)-flavor symmetries. Here we argue that in the molecular picture the $Y(4230)$ (or $Y(4260)$), the $Y(4360)$ and the recently discovered $Y(4500)$ and $Y(4620)$ vector-like resonances are linked by these two symmetries. By formulating a contact-range effective field theory for the $D \bar{D}_1$ and $D_s \bar{D}_{s1}$ family of S- and P-wave charmed meson-antimeson systems, we find that if the $Y(4230)$ were to be a pure $D \bar{D}_1$ molecular state, there would be a $D^* \bar{D}_1$ partner with a mass similar to the $Y(4360)$, a $D_s \bar{D}_{s1}$ partner with a mass close to the $Y(4500)$ and three $J=1,2$ $D_s^* \bar{D}_{s1}$ and $J=3$ $D_s^* \bar{D}_{s2}^{*}$ bound states with a mass in the vicinity of $4630\,{\rm MeV}$, of which the first one ($J=1$) might correspond with the $Y(4620)$. The previous predictions can in turn be improved by modifying the assumptions we have used to build the effective field theory. In particular, if we consider the closeness of the $D^* \bar{D}_1$-$D^* \bar{D}_2^*$ and $D_s^* \bar{D}_{s1}$-$D_s^* \bar{D}_{s2}^*$ thresholds and include the related coupled channel dynamics, we predict a $J=2$ positive C-parity state with a mass around $4650\,{\rm MeV}$. This hidden-strange and hidden-charm state might in turn be identified with the $X(4630)$ that has been discovered past year by the LHCb in the $J/\psi \phi$ invariant mass distribution.

QCD sum rule study for hidden-strange pentaquarks* *Supported by the National Natural Science Foundation of China (12175318), the National Key R & D Program of China (2020YFA0406400) and the Fundamental Research Funds for the Central Universities

Inspired by the LHCb observations of hidden-charm states, we study their hidden-strange analog states in both the and configurations. We investigate pentaquark states in the , , , , and structures with and and with and calculate their masses in the framework of QCD sum rules. Our numerical results show that the extracted hadron masses for all the , , , , and structures are significantly higher than the mass threshold, and the masses for and are also higher than the threshold of the corresponding hadron; hence, no bound state exists in such channels, which is consistent with the current experimental status.

Impact of a thermal medium on newly observed Z_{cs}(3985) resonance and its b-partner

Motivated by the very recent discovery of the strange hidden-charm exotic state Z_{cs}(3985) by the BESIII Collaboration, we study the possible interpretation of this exotic state the both at T=0 and Tne 0 . We analytically compute the mass and meson-current coupling constant of this resonance with spin-parity J^{P} = 1^+ at finite temperature approximation up to the sixth order of the thermal operator dimension including non-perturbative contributions. Extracting thermal mass and meson-current coupling constant sum rules, the modifications on properties of the Z_{cs}(3985) state in hot medium are determined. As a by-product, the hadronic parameters of the bottom partner of Z_{cs}(3985) is estimated as well. The search for temperature effects on the hadronic parameters of the hidden-charm meson Z_{cs}(3985) and the bottom partner enable us to understand the phase transitions, chiral symmetry breaking, and the properties of hot-dense matter in QCD. Moreover, the full width of the resonance Z_{cs}(3985) is calculated as (12.0pm 0.8)~{mathrm {MeV}} using the strong decay in the tetraquark picture. Results for width and mass are in reasonable agreement with existing experimental data and results of other theoretical works. The information obtained about the parameters of the considered states is useful for experimental investigations of exotic mesons.

Hunting for the heavy quark spin symmetry partner of Z_{cs}

The discovery of a charged strange hidden-charm state Z_{cs}(3985) implies another higher Z^*_{cs} state coupling to {bar{D}}_s^{*-}D^{*0} + c.c under the heavy quark spin symmetry. In this paper we discuss a possible hunt for it with data taken at existing facilities. We point out a hint for Z^*_{cs} in the data of {bar{B}}_s^0 rightarrow J/psi K^- K^+ at LHCb, though weak, in line with the production mechanism of pentaquark P_c. We also study the triangular singularity which would possibly enhance the production of Z^*_{cs} in electron-positron collision. Surprisingly, the production rate of Z^*_{cs} is expected to be maximum at the e^+ e^- center of mass energy of 4.648 GeV, which is lower than 4.681 GeV for Z_{cs} due to the inverted coupling hierarchy of D_{s1}{bar{D}}^* K and D_{s2}{bar{D}}K in the triangle diagrams. Their bottom analogue under heavy quark flavor symmetry is also discussed. Our theoretical analysis would confront with future experiment of LHCb, BESIII, and Bell II.

Semi-inclusive lepto-production of hidden-charm exotic hadrons * *Supported in part by the Chinese Academy of Sciences (CAS) (XDB34030000, QYZDB-SSW-SYS013), the National Natural Science Foundation of China (NSFC) (11835015, 12047503, 11961141012, 11847301), the Fundamental Research Funds for the Central Universities (2019CDJDWL0005) and NSFC and the Deutsche Forschungsgemeinschaft (DFG) through the Sino-German Collaborative Research Center “Symmetries and the Emergence of Structure in

We investigate the semi-inclusive production of hidden-charm exotic states, including the , , and pentaquark states, in lepton-proton scattering processes. These hadrons are close to the thresholds of a pair of charm and anticharm hadrons and are assumed to possess a hadronic molecular structure as their main feature. To provide order-of-magnitude estimates of the cross sections, we use Pythia to simulate the short-distance productions of the constituent hadrons, which then rescatter to form exotic hadrons. The estimates for the and states are not in conflict with the upper limits measured in the COMPASS experiment for the exclusive photoproduction process. The results indicate that the considered hidden-charm states can be copiously produced at the proposed electron-ion colliders EicC and US-EIC.

Study on Zcs and excited Bs0 states in the chiral quark model

Stimulated by the newly observed charged hidden-charm state ${Z}_{cs}(3985{)}^{\ensuremath{-}}$ by BESIII Collaboration, ${Z}_{cs}(4000{)}^{+}$, ${Z}_{cs}(4220{)}^{+}$ and the excited ${B}_{s}^{0}$ states by LHCb Collaboration, a full calculation including masses, decay widths, and the inner structures of the states has emerged in the chiral quark model. For ${Z}_{cs}$ states, we assign quantum numbers $I({J}^{P})=\frac{1}{2}({1}^{+})$ and quark composition $c\overline{c}s\overline{u}$ according to the experiment. For ${B}_{s}^{0}$ states, systematically, investigations are performed with $I({J}^{P})=0({0}^{+}),0({1}^{+}),0({2}^{+})$ in both two-body $b\overline{s}$ and four-body $b\overline{s}q\overline{q}$ ($q=u$ or $d$) systems. Each tetraquark calculation takes all structures including meson-meson, diquark-antidiquark, and all possible color configurations into account. Among the numerical techniques to solve the two-body and four-body Schr\"odinger equation, the spatial wave functions are expanded in series of Gaussian basis functions for high precision, which is the way Gaussian expansion method (GEM) so called. Our results indicate that the low-lying states of the four-quark system are all higher than the corresponding thresholds either for $c\overline{c}s\overline{u}$ or for $b\overline{s}q\overline{q}$ systems. With the help of the real scaling method, we found two molecular resonance states with masses of 4023 and 4042 MeV for the $c\overline{c}s\overline{u}$ system. The state $c\overline{c}s\overline{u}(4042)$ has a close mass and decay width with the recent observed state ${Z}_{cs}(3985{)}^{\ensuremath{-}}$. For the $b\overline{s}q\overline{q}$ system with $J=0$, some resonance states are also found. The newly observed excited ${B}_{s}^{0}$ states can be accommodated in the chiral quark model as $2S$ or $1D$ states, and the mixing with four-quark states also needs to be considered.

Photoproduction of strange hidden-charm and hidden-bottom states

Recently BESIII collaboration discovered a charged strange hidden-charm state Z_{cs}(3985) in the D_s^-D^{*0} + D_s^{*-}D^{0} spectrum. A higher Z'_{cs} state coupling to {bar{D}}_s^{*-}D^{*0} is expected by SU(3)-flavor symmetry, and their bottom partners are anticipated by heavy quark flavor symmetry. Here we study the photoproduction of these exotic states and investigate carefully the background from Pomeron exchange. Our results indicate that the maximal photoproduction cross section of strange partner is around 1–2 orders of magnitude smaller than that of the corresponding non-strange states. The possibility of searching for them in future electron-ion colliders (EIC) is briefly discussed.

ATLAS results on quarkonia and heavy flavor production

The associated production a vector boson with [Formula: see text] is a key observable for understanding of the quarkonium production mechanisms, including the separation of single and double parton scattering components. Measurements from the ATLAS detector at LHC on quarkonium production, including associated production of a [Formula: see text] and [Formula: see text] are presented. A study of the hidden-charm states [Formula: see text] is also provided.

Molecular Xi _{bc} states from meson\u2013baryon interaction

We have studied the meson–baryon interaction in coupled channels with the same quantum numbers of Xi _{bc}. The interaction is attractive in some channels and of sufficient intensity to lead to bound states or resonances. We use a model describing the meson–baryon interaction based on an extrapolation of the local hidden gauge approach to the heavy sector, which has been successfully used in predicting Omega _c and hidden charm states. We obtain many states, some of them narrow or with zero width, as a consequence of the interaction, which qualify as molecular states in those channels. The success in related sectors of the picture used should encourage the experimental search for such states.

Doubly hidden-charm/bottom QQQQ tetraquark states

We study the mass spectra for the cccc and bbbb tetraquark states by developing a moment sum rule method. Our results show that the bbbb tetraquarks lie below the threshold of ηb(1S) ηb(1S ). They are probably stable and very narrow. The masses for the doubly hidden-charm states cccc are higher than the spontaneous dissociation thresholds of two charmonium mesons. We suggest to search for such states in the J/Ψ/J/Ψ and Ψc(1S) Ψc(1S) channels.

Hunting for exotic doubly hidden-charm/bottom tetraquark states

We develop a moment QCD sum rule method augmented by fundamental inequalities to study the existence of exotic doubly hidden-charm/bottom tetraquark states made of four heavy quarks. Using the compact diquark–antidiquark configuration, we calculate the mass spectra of these tetraquark states. There are 18 hidden-charm ccc¯c¯ tetraquark currents with JPC=0++, 0−+, 0−−, 1++, 1+−, 1−+, 1−−, and 2++. We use them to perform QCD sum rule analyses, and the obtained masses are all higher than the spontaneous dissociation thresholds of two charmonium mesons, which are thus their dominant decay modes. The masses of the corresponding hidden-bottom bbb¯b¯ tetraquarks are all below or very close to the thresholds of the ϒ(1S)ϒ(1S) and ηb(1S)ηb(1S), except one current of JPC=0++. Hence, we suggest to search for the doubly hidden-charm states in the J/ψJ/ψ and ηc(1S)ηc(1S) channels.

Hidden-charm pentaquarks and their hidden-bottom and Bc -like partner states

In the framework of the color-magnetic interaction, we have systematically studied the mass splittings of the possible hidden-charm pentaquarks $qqqc\overline{c}$ ($q=u$, $d$, $s$) where the three light quarks are in a color-octet state. We find that (i) the LHCb ${P}_{c}$ states fall in the mass region of the studied system, (ii) most pentaquarks should be broad states since their $S$-wave open-charm decays are allowed while the lowest state is the ${J}^{P}={\frac{1}{2}}^{\ensuremath{-}}$ $\mathrm{\ensuremath{\Lambda}}$-like pentaquark with probably the suppressed ${\ensuremath{\eta}}_{c}\mathrm{\ensuremath{\Lambda}}$ decay mode only, and (iii) the ${J}^{P}={\frac{5}{2}}^{\ensuremath{-}}$ states do not decay through the $S$ wave and their widths are not so broad. The masses and widths of the two LHCb ${P}_{c}$ baryons are compatible with such pentaquark states. We also explore the hidden-bottom and ${B}_{c}$-like partners of the hidden-charm states and find the possible existence of the pentaquarks which are lower than the relevant hadronic molecules.

Measurements of \u03c8(2S) and X(3872) \u2192 J/\u03c8\u03c0+\u03c0\u2212 production in pp collisions at sqrt{s}=8 TeV with the ATLAS detector

Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and ψ(2S), in the decay mode J/ψπ+π−, measured using 11.4 fb−1 of pp collisions at sqrt{s}=8 TeV by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/ψ(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and ψ(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and ψ(2S) production gives {R}_B=frac{mathrm{mathcal{B}}left(Bto X(3872)+mathrm{any}right)mathrm{mathcal{B}}left(X(3872)to J/psi {pi}^{+}{pi}^{-}right)}{mathrm{mathcal{B}}left(Bto psi (2S)+mathrm{any}right)mathrm{mathcal{B}}left(psi (2S)to J/psi {pi}^{+}{pi}^{-}right)}=left(3.95pm 0.32left(mathrm{s}mathrm{tat}right)pm 0.08left(mathrm{s}mathrm{y}mathrm{s}right)right)times {10}^{-2} separating short- and long-lived contributions, assuming that the short-lived component is due to Bc decays, gives RB = (3.57 ± 0.33(stat) ± 0.11(sys)) × 10−2, with the fraction of non-prompt X(3872) produced via Bc decays for pT(X(3872)) > 10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and ψ(2S) decays are also measured and compared to theoretical predictions.

Photoproduction of hidden-charm states in the reaction near threshold**Supported by Major State Basic Research Development Program in China (2014CB845400), National Natural Science Foundation of China (11475227, 11275235, 11035006) and Chinese Academy of Sciences (Knowledge Innovation Project (KJCX2-EW-N01), Youth Innovation Promotion Association CAS (2016367), Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of

We report on a theoretical study of the hidden charm states in the reaction near threshold within an effective Lagrangian approach. In addition to the contributions from the s-channel nucleon pole, the t-channel D0 exchange, the u-channel exchange and the contact term, we study the contributions from the states with spin-parity JP = 1/2− and 3/2−. The total and differential cross sections of the reaction are predicted. It is found that the contributions of these states give clear peak structures in the total cross sections. Thus, this reaction is another new platform to study the hidden-charm states. It is expected that our model calculation may be tested by future experiments.

Λb→J/ψK0Λreaction and a hidden-charm pentaquark state with strangeness

We study the $\Lambda_{b}\rightarrow J/\psi K^{0}\Lambda$ reaction considering both the $K^{0}\Lambda$ interaction with its coupled channels and the $J/\psi\Lambda$ interaction. The latter is described by taking into account the fact that there are predictions for a hidden-charm state with strangeness that couples to $J/\psi\Lambda$. By using the coupling of the resonance to $J/\psi\Lambda$ from these predictions we show that a neat peak can be observed in the $J/\psi\Lambda$ invariant mass distribution, rather stable under changes of unknown magnitudes. In some cases, one finds a dip structure associated to that state, but a signal of the state shows up in the $J/\psi$ spectrum.

Perspective study of exotics and flavour baryons in antiproton-proton annihilation and proton-proton collisions

Abstract. The spectroscopy of exotic states with hidden charm is discussed. Together with charmonium, these provide a good tool for testing theories of the strong interactions including both perturbative and non-perturbative QCD, lattice QCD, potential and other phenomenological models. An elaborated analysis of exotics spectrum is given, and attempts to interpret recent experimentally observed states with masses above the DD threshold region are considered. Experimental results from different collaborations (BES, BaBar, Belle, LHCb) are analyzed with special attention given to recently discovered hidden charm states. Some of these states can be interpreted as higher-lying charmonium states and others as tetraquarks with hidden charm. It has been shown that charged/neutral tetraquarks must have their neutral/charge partners with mass values differ by at most a few MeV/c 2 , hypotheses that tend to coincide with those proposed by Maiani and Polosa. However, measurements of different decay modes are needed before firm conclusions can be made. These data can be derived directly from the experiments using ahigh quality antiproton beam with momentum up to 15 GeV/c and proton-proton collisions with momentum up to 26 GeV/c. DD

Perspective study of charmonium and exotics above the D $$\bar D$$ threshold

The spectroscopy of exotic states with hidden charm is discussed. Together with charmonium, these provide a good tool for testing theories of the strong interactions including both perturbative and nonperturbative QCD, lattice QCD, potential and other phenomenological models. An elaborated analysis of exotics spectrum is given, and attempts to interpret recent experimentally observed states with masses above the D $$\bar D$$ threshold region are considered. Experimental results from different collaborations (BES, BaBar, Belle, LHCb) are analyzed with special attention given to recently discovered hidden charm states. Some of these states can be interpreted as higher-lying charmonium states and others as tetraquarks with hidden charm. It has been shown that charged/neutral tetraquarks must have their neutral/charge partners with mass values differing by at most a few MeV. However, measurements of different decay modes are needed before firm conclusions can be made. These data can be derived directly from the experiments using a high quality antiproton beam with momentum up to 15 GeV/c and proton–proton collisions with momentum up to 26 GeV/c.

Perspective study of exotics above the threshold

The spectroscopy of exotic states with hidden charm is discussed. Together with charmonium, these provide a good tool for testing theories of the strong interactions including both perturbative and non-perturbative QCD, lattice QCD, potential and other phenomenological models. An elaborated analysis of exotics spectrum is given, and attempts to interpret recent experimentally observed states with masses above the threshold region are considered. Experimental results from different collaborations (BES, BaBar, Belle, LHCb) are analyzed with special attention given to recently discovered hidden charm states. Some of these states can be interpreted as higher-lying charmonium states and others as tetraquarks with hidden charm. It has been shown that charged/neutral tetraquarks must have their neutral/charge partners with mass values differing by at most a few MeV c−2, hypotheses that tend to coincide with those proposed by Maiani and Polosa. However, measurements of different decay modes are needed before firm conclusions can be made. These data can be derived directly from experiments using a high quality antiproton beam with momentum up to 15 GeV c−1 and proton–proton collisions with momentum up to 26 GeV c−1.

Identifying Exotic Hidden-Charm Pentaquarks.

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.

Hidden-charm tetraquarks and chargedZcstates

Experimentally several charged axial-vector hidden-charm states were reported. Within the framework of the color-magnetic interaction, we have systematically considered the mass spectrum of the hidden-charm and hidden-bottom tetraquark states. It is impossible to accommodate all of the three charged states ${Z}_{c}(3900)$, ${Z}_{c}(4025)$, and ${Z}_{c}(4200)$ within the axial-vector tetraquark spectrum simultaneously. Not all of these three states are tetraquark candidates. Moreover, the eigenvector of the chromomagnetic interaction contains valuable information of the decay pattern of the tetraquark states. The dominant decay mode of the lowest axial-vector tetraquark state is $J/\ensuremath{\psi}\ensuremath{\pi}$ while its ${D}^{*}\overline{D}$ and ${\overline{D}}^{*}{D}^{*}$ modes are strongly suppressed, which is in contrast with the fact that the dominant decay mode of ${Z}_{c}(3900)$ and ${Z}_{c}(4025)$ is $\overline{D}{D}^{*}$ and ${\overline{D}}^{*}{D}^{*}$, respectively. We emphasize that all the available experimental information indicates that ${Z}_{c}(4200)$ is a very promising candidate of the lowest axial-vector hidden-charm tetraquark state.