Hidden Charm Research Articles

Investigation of potential for heavy tetraquarks with hidden charm

Investigation of potential for heavy tetraquarks with hidden charm

$$N^*$$ states with hidden charm and a three-body nature

In this work we study the formation of $N^*$'s as a consequence of the dynamics involved in the $ND\bar D^*-N\bar D D^*$ system when the $D\bar D^*-\bar D D^*$ subsystem generates $X(3872)$ in isospin 0 and $Z_c(3900)$ in isospin 1. States with isospin $I=1/2$ and mass in the energy region $4400-4600$ MeV are obtained with spin-parity $J^P=1/2^+$ and $3/2^+$, predicting in this way the existence of $N^*$ resonances with hidden charm and a three-body nature.

Spectrum of hidden-charm, open-strange exotics in the dynamical diquark model

The observation by BESIII and LHCb of states with hidden charm and open strangeness ($c\bar c q\bar s$) presents new opportunities for the development of a global model of heavy-quark exotics. Here we extend the dynamical diquark model to encompass such states, using the same values of Hamiltonian parameters previously obtained from the nonstrange and hidden-strange sectors. The large mass splitting between $Z_{cs}(4000)$ and $Z_{cs}(4220)$ suggests substantial SU(3)$_{\rm flavor}$ mixing between all $J^P \! = \! 1^+$ states, while their average mass compared to that of other sectors offers a direct probe of flavor octet-singlet mixing among exotics. We also explore the inclusion of $\eta$-like exchanges within the states, and find their effects to be quite limited. In addition, using the same diquark-mass parameters, we find $P_c(4312)$ and $P_{cs}(4459)$ to fit well as corresponding nonstrange and open-strange pentaquarks.

Configuration mixing in strange tetraquarks Zcs

The BESIII Collaboration has observed a candidate for a $c \bar c s \bar u$ tetraquark $Z_{cs}$ at $(3982.5^{+1.8}_{-2.6} \pm 2.1)$ MeV and width $(12.8^{+5.3}_{-4.4} \pm 3.0)$ MeV, while the LHCb Collaboration has observed a $Z_{cs}$ candidate in the $\jpsi K^-$ channel with mass of $(4003 \pm 6 ^{+4}_{-14})$ MeV and width $(131 \pm 15 \pm 26)$ MeV. In this note we examine the possibility that these two states are distinct eigenstates of a mixing process similar to that which gives rise to two axial-vector mesons labeled by the Particle Data Group $K_1(1270)$ and $K_1(1400)$. The main point is that on top of a $\bar c c$ pair, the $Z_{cs}$ states have the same light quark content as the $K_1$-s. In the compact tetraquark picture this implies several additional states, analogous to members of the $K_1$ nonet. These states have not yet been observed, nor are they required in the molecular approach. Thus experimental discovery or exclusion of these extra states will be a critical test for competing models of exotic mesons with hidden charm.

Hypothesis of Intrinsic Charm in the Proton and Pentaquarks with a Hidden Flavor

New upper limits on the intrinsic-charm contribution to the proton are obtained on the basis of experimental data on the existence of pentaquarks involving a hidden charm. Possible distributions of heavy quarks within the proton are analyzed.

A phenomenological analysis on isospin-violating decay of X(3872)

In a molecular scenario, we investigate the isospin-breaking hidden charm decay processes of X(3872), i.e., X(3872) rightarrow pi ^+ pi ^- J/psi , X(3872) rightarrow pi ^+ pi ^- pi ^0 J/psi , and X(3872)rightarrow pi ^0chi _{cJ}. We assume that the source of the strong isospin violation comes from the different coupling strengths of X(3872) to its charged components D^{*+} D^- and neutral components D^{*0 } {bar{D}}^0 as well as the interference between the charged meson loops and neutral meson loops. The former effect could fix our parameters by using the measurement of the ratio Gamma [X(3872) rightarrow pi ^+ pi ^- pi ^0 J/psi ]/Gamma [X(3872) rightarrow pi ^+ pi ^- J/psi ]. With the determined parameter range, we find that the estimated ratio Gamma [X(3872) rightarrow pi ^0 chi _{c1}/Gamma [X(3872) rightarrow pi ^+ pi ^- J/psi ] is well consistent with the experimental measurement from the BESIII collaboration. Moreover, the partial width ratio of pi ^0 chi _{cJ} for J=0,1,2 is estimated to be 1.77{-}1.65:1:1.09{-}1.43, which could be tested by further precise measurements of BESIII and Belle II.

ATLAS measurements of production, decays and spectroscopy of heavy flavour hadrons

Recent results from the ATLAS experiment on production, decays and spectroscopy of heavy flavour hadrons are presented. The latest results on CP-violation in Bs → J/ψϕ, decays are discussed. Measurements of the inclusive and associated charmonium production are also reported. In addition, searches for pentaquarks with hidden charm and recent results on Bc meson production and decays are highlighted.

K+Λ(1405) photoproduction at the BGO-OD experiment

Since the discovery of the Λ(1405), it remains poorly described by conventional constituent quark models, and it is a candidate for having an “exotic” meson-baryon or “penta-quark” structure, similar to states recently reported in the hidden charm sector.The Λ(1405) can be produced in the reactionγpK+Λ(1405). The pure I=0 decay mode into Σ0π0is prohibited for the mass-overlapping Σ(1385). Combining a large aperture forward magnetic spectrometer and a central BGO crystal calorimeter, the BGO-OD experiment is ideally suited to measure this decay with theK+in the forward direction. Preliminary results are presented.*Supported by DFG (PN 388979758, 405882627)

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.

Nucleon resonances with hidden charm in γp reactions

The excitations of nucleon resonances with hidden charm, $N^*_{c\bar{c}}$, in the $\gamma p$ reactions are investigated by using the predictions from the available meson-baryons (MB) coupled-channel models. For the $\gamma\,p\rightarrow J/\psi\, p$ process, we first calculate the Pomeron-exchange amplitudes with the parameters determined from fitting the available total cross section data up to invariant mass $W=300$ GeV. We then add the resonant amplitudes to examine the effects of $ N^*_{c\bar{c}}$ excitations on the cross sections of $\gamma\,p\rightarrow J/\psi\, p$ in the near threshold energy region. The $N^*_{c\bar{c}}\to MB$ transition matrix elements are determined from the partial decay widths predicted by the meson-baryons coupled-channel models. The $\gamma p \to N^*_{c\bar{c}}$ transition amplitudes are calculated from the Vector Meson Dominance (VMD) model. The total $\gamma p\rightarrow J/\psi\, p$ amplitudes then depend on an off-shell form factor, parameterized as $F_V(q^2)=\Lambda^4/(\Lambda^4 + (q^2 - m^2_V)^2)$ with $\Lambda=550$ MeV. We then demonstrate that the $N^*_{c\bar{c}}$ can be most easily identified in the differential cross sections at large angles of outgoing $J/\psi$ where the contribution from Pomeron-exchange becomes negligible. With the same VMD model and the same coupled-channel models of $N^*_{c\bar{c}}$, we also calculate the resonant amplitudes for the $\gamma\,p\rightarrow Vp\rightarrow N^*_{c\bar{c}} \rightarrow \bar{D}^0\Lambda_c^+ (\bar{D}^{*0}\Lambda_c^+)$ processes. By adding the non-resonant amplitudes due to the exchange of $\bar{D}^{*0}$ ($\bar{D}^{0})$, we then predict the cross sections of $\gamma\,p\rightarrow \bar{D}^0\Lambda_c^+(\bar{D}^{*0}\Lambda^+_c)$ for additional experimental tests of the available meson-baryon coupled-channel models of $N^*_{c\bar{c}}$.

Decays of pentaquarks in hadrocharmonium and molecular scenarios

We consider decays of the hidden charm LHCb pentaquarks in the hadrocharmonium and molecular scenarios. In both pictures the LHCb pentaquarks are essentially nonrelativistic bound states. We develop a semirelativistic framework for calculation of the partial decay widths that allows the final particles to be relativistic. Using this approach we calculate the decay widths in the hadrocharmonium and molecular pictures. Molecular hidden charm pentaquarks are constructed as loosely bound states of charmed and anticharmed hadrons. Calculations show that molecular pentaquarks decay predominantly into states with open charm. Strong suppression of the molecular pentaquark decays into states with hidden charm is qualitatively explained by a relatively large size of the molecular pentaquark. The decay pattern of hadrocharmonium pentaquarks that are interpreted as loosely bound states of excited charmonium $\psi'$ and nucleons is quite different. This time dominate decays into states with hidden charm, but suppression of the decays with charm exchange is weaker than in the respective molecular case. The weaker suppression is explained by a larger binding energy and respectively smaller size of the hadrocharmonium pentaquarks. These results combined with the experimental data on partial decay widths could allow to figure out which of the two theoretical scenarios for pentaquarks (if either) is chosen by nature.

B decays: A factory for hidden charm multiquark states

We assume that the two hidden charm pentaquark discovered at $LHCb$ are built by the three light quarks and the $c \bar{c}$ pair, both colour octets. in relative P-wave for the $\frac{5}{2}^+$ state and by the eigenvectors of the chromomagnetic interaction for the five constituents in S-wave for the four $\frac{3}{2}^-$ state with masses $4360$, $4410$, $4490$ and $4560$ MeV . The "open channel" $p $ $J/\psi$ has large components along the two first states and so appear as the $4380$ resonance and the $\Lambda_c$ $ \bar{D}^{0*}$ and $\Sigma_c$ $\bar{D}^*$ are "open channels" for the lower and higher resonances, respectively. The expectation for their strange isoscalar partners is to have a mass larger by an amount of the order or smaller than the $M_{\Lambda} - M_N$ mass difference. We account for the small width of the $\frac{5}{2}^+$, since its decay needs the exchangeof a gluon and stress that the decays of particles with "beauty" provide the best experimental framework for the discovery of hidden charm multiquarks. The relevance of the production mechanics shows the reason why only some of the states with non minimal number of constituents have been found.

What is the right formalism to search for resonances? II. The pentaquark chain

We discuss the differences between several partial-wave analysis formalisms used in the construction of three-body decay amplitudes involving fermions. Specifically, we consider the decay Lambda _b rightarrow psi ,p K^-, where the hidden charm pentaquark signal has been reported. We analyze the analytical properties of the amplitudes and separate kinematical and dynamical singularities. The result is an amplitude with the minimal energy dependence compatible with the S-matrix principles.

K⁎ mesons with hidden charm arising from KX(3872) and KZc(3900) dynamics

Inspired by the recent discovery of the pentaquark states Pc(4450) and Pc(4380), which can be viewed as excited nucleon states with hidden charm, we study the three-body interaction of a kaon and a pair of DD¯⁎ in isospin 0 and 1. We show that the two body interactions stringently constrained by the existence of the Ds0⁎(2317), Ds1⁎(2460), X(3872), and Zc(3900), which are widely believed to contain large DK, D⁎K, and DD¯⁎ components, inevitably lead to the existence of a heavy K⁎ meson with hidden charm. Concrete coupled channel three-body calculations yield its mass and width as (4307±2)−i(9±2)MeV with I(JP)=1/2(1−). This state, if found experimentally, definitely cannot be accommodated in a qq¯ picture, and therefore presents a clear case of an exotic hadron.

D*D*D¯ and D*D*D¯* three-body systems

The hidden charm $X(3872)$ resonance is usually thought to be a $D^{*0} \bar{D}^0$ meson-antimeson molecule with quantum numbers $J^{PC} = 1^{++}$. If this is the case, there is the possibility that there might be three body bound states with two charmed mesons and a charmed antimeson. Here we argue that the theoretical existence of this type of three body molecules is expected from heavy quark spin symmetry. If applied to the two body sector, this symmetry implies that the interaction of the $D^{*0} \bar{D}^{*0}$ meson-antimeson pair in the $J^{PC} = 2^{++}$ channel is the same as in the $J^{PC} = 1^{++}$ $D^{*0} \bar{D}^0$ case. From this we can infer that the $J^P = 3^{-}$ $D^{*0} D^{*0} \bar{D}^{*0}$ molecule will be able to display the Efimov effect if the scattering length of the $2^{++}$ channel is close enough to the unitary limit. Heavy quark spin symmetry also indicates that the $J^P = 2^{-}$ $D^{*0} D^{*0} \bar{D}^0$ molecule is analogous to the $J^P = 3^{-}$ $D^{*0} D^{*0} \bar{D}^{*0}$ one. That is, it can also have a geometric spectrum. If we consider these triply heavy trimers in the isospin symmetric limit, the Efimov effect disappears and we can in principle predict the fundamental state of the $2^-$ $D^*D^*\bar{D}$ and $3^-$ $D^* D^* \bar{D}^*$ systems. The same applies to the $B^*B^* \bar{B}^*$ system: if the $Z_b(10650)$ is an isovector $B^* \bar{B}^*$ molecule then the $0^-$ isodoublet and the $1^-$, $2^-$ isoquartet $B^* B^* \bar{B}^*$ trimers might bind, but do not display Efimov physics. Finally from heavy flavour symmetry it can be argued that scattering in the $B D$ two-body system might be resonant. This would in turn imply the possibility of Efimov physics in the $B B D$ three body system.

S wave hidden charm–hidden strangeness production in e+e− annihilation

It is suggested that the recently observed enhancement of the relative yield in e+e− annihilation of states with hidden charm and hidden strangeness above 4.43 GeV is associated with the S wave production of the charmed strange meson pairs Ds0(2317)D¯s⁎+c.c. and Ds1⁎(2460)D¯s+c.c. This mechanism implies a pattern of breaking of the Heavy Quark Spin Symmetry (HQSS) that can be tested in the final channels such as ηc(1S)ϕ, hc(1P)η, hc(1P)η′ produced in the same energy range.

Bayesian study of relativistic open and hidden charm in anisotropic lattice QCD

We present the first combined study of correlators and spectral properties of charmonium and open-charm-mesons at finite temperature using a fully relativistic lattice QCD approach. The QCD medium is captured by second generation anisotropic 24^3xN_t lattices from the FASTSUM collaboration, including 2+1 flavors of clover discretized quarks with m_pi~380 MeV. Two Bayesian methods are deployed to reconstruct the spectral functions, the recent BR method as well as the Maximum Entropy Method with Fourier basis. We take particular care to disentangle genuine in-medium effects from method artifacts with the help of the reconstructed correlator. Consistent with the direct inspection of correlators, we observe no significant in-medium modification for J/Psi and eta_c around the crossover, while the chi_c states on the other hand show clear changes around the transition. At the highest temperature, T=352 MeV, J/Psi and eta_c also exhibit discernible changes compared to the vacuum. For D mesons around $T_c$, no significant modifications are observed, but we find clear indications that no bound state survives at the highest temperature of T=352 MeV. Above T_c we discover a significant difference between D and D* mesons, the latter being much more strongly affected by the medium.

Masses of Charmed and Bottom Tetraquarks in the Non-Relativistic Quark Model

Heavy tetraquark states are studied within the diquark-antidiquark picture in the framework of a simple constituent quark model. Considering hyperfine spin and isospin interactions, we predict the masses of the scalar diquarks and of the open and hidden charmed and bottom scalar tetraquarks. Our results indicate the scalar resonances [Formula: see text] and [Formula: see text] have a sizable tetraquark amount in their wave function, while it turns out the scalar state [Formula: see text] should not be considered as being predominately diquark-antidiquark bound states.

New Look at Hidden Charm Tetra and Pentaquark States

New Look at Hidden Charm Tetra and Pentaquark States

Heavy and strange holographic baryons

We extend the $D4$-$D8$ holographic construction to include three chiral and one heavy flavor, to describe heavy-light baryons with strangeness and their exotics. At strong coupling, the heavy meson always binds to the bulk instanton in the form of a flavor zero mode in the fundamental representation. We quantize the ensuing bound states using the collective quantization method, to obtain the spectra of heavy and strange baryons with both explicit and hidden charm and bottom. Our results confirm the existence of two low-lying charmed penta-quark states with $\frac 12^-,\frac 32^-$ assignments, and predict many new ones with both charm and bottom. They also suggest a quartet of low-lying neutral $\Omega_c^0$ with assignments $\frac 12^\pm ,\frac 32^\pm$ that are heavier than the quintuplet of neutral $\Omega_c^0$ recently reported by LHCb.