Search

A discussion is presented of the estimates of the energy and width of resonances in constituent models, with focus on the tetraquark states containing heavy quarks. [ABSTRACT FROM AUTHOR]

We study the strong decays of the ϕ (2170) , along with its possible partner X (2436) , as two fully strange tetraquark states of J P C = 1 − − . These two states are assumed to contain two strange quarks and two anti-strange quarks, with the flavor symmetry 6 s s ⊗ 6 ¯ s ¯ s ¯ . We consider seven decay channels: ϕ η , ϕ η ′ , ϕ f 0 (980) , ϕ f 1 (1420) , h 1 (1415) η , h 1 (1415) η ′ , and h 1 (1415) f 1 (1420) . Some of these channels are kinematically possible, and we calculate their relative branching ratios through the Fierz rearrangement. Future experimental measurements on these ratios could be useful in determining the nature of the ϕ (2170) and X (2436) . The ϕ (2170) has been observed in the ϕ f 0 (980) , ϕ η , and ϕ η ′ channels, and we propose to further examine it in the h 1 (1415) η channel. Evidences of the X (2436) have been observed in the ϕ f 0 (980) channel, and we propose to verify whether this structure exists or not in the ϕ η , ϕ η ′ , h 1 (1415) η , and h 1 (1415) η ′ channels. [ABSTRACT FROM AUTHOR]

We review the semi-inclusive hadroproduction of a neutral hidden-flavor tetraquark with light and heavy quark flavor at the HL-LHC, accompanied by another heavy hadron or a light-flavored jet. We make use of the novel TQHL1.0 determinations of leading-twist fragmentation functions to describe the formation mechanism of a tetraquark state within the next-to-leading order perturbative QCD. This framework builds on the basis of a spin physics-inspired model, taken as a proxy for the lowest-scale input of the constituent heavy-quark fragmentation channel. Then, all parton-to-tetraquark fragmentation functions are consistently obtained via the above-threshold DGLAP evolution in a variable-flavor number scheme. We provide predictions for a series of differential distributions calculated by the hands of the JETHAD method, well-adapted to NLL / NLO + hybrid-factorization studies, where the resummation of next-to-leading energy logarithms and beyond is included in the collinear picture. We provide corroborating evidence that high-energy observables sensitive to semi-inclusive tetraquark emissions at the HL-LHC exhibit a fair stability under radiative corrections, as well as MHOU studies. Our analysis constitutes a prime contact point between QCD resummations and the exotic matter. [ABSTRACT FROM AUTHOR]

The X 1 7 particle, discovered by [A. J. Krasznahorkay et al., Phys. Rev. Lett.116, 042501 (2016), doi:10.1103/PhysRevLett.116.042501] at ATOMKI, was recently confirmed in the γ γ invariant mass spectra by [K. U. Abraamyan, C. Austin, M. I. Baznat, K. K. Gudima, M. A. Kozhin, S. G. Reznikov and A. S. Sorin, arXiv:2311.18632] at JINR. We notice with surprise and interest that the X 1 7 seems to have a double-peak structure. This is in a possible coincidence with our QCD sum rule study of [H.-X. Chen, arXiv:2006.01018], where we interpreted the X 1 7 as a tetraquark state composed of four bare quarks (u ū d d ̄), and claimed that "A unique feature of this tetraquark assignment is that we predict two almost degenerate states with significantly different widths". These two different tetraquark states are described by two different chiral tetraquark currents ū L γ μ d L d ̄ L γ μ u L and ū L γ μ d L d ̄ R γ μ u R . To verify whether the tetraquark assignment is correct or not, we replace the up and down quarks by the strange quarks, and apply the QCD sum rule method to study the other four chiral tetraquark currents ū L γ μ s L s ̄ L γ μ u L , ū L γ μ s L s ̄ R γ μ u R , d ̄ L γ μ s L s ̄ L γ μ d L and d ̄ L γ μ s L s ̄ R γ μ d R . We calculate their correlation functions, and find that non-perturbative QCD effects do not contribute much to them. Our results suggest that there may exist four almost degenerate tetraquark states with masses about 2 3 6 ∼ 2 9 6  MeV. Each of these states is composed of four bare quarks, either u ū s s ̄ or d d ̄ s s ̄. [ABSTRACT FROM AUTHOR]

Dedicated to the memory of our colleague, Harald Fritzsch, who, together with Murray Gell-Mann, introduced the color quantum number as the exact symmetry responsible for the strong interaction, thus establishing quantum chromodynamics (QCD) as a fundamental non-Abelian gauge theory. A basic understanding of hadron properties, however, such as confinement and the emergence of a mass scale, from first principles QCD has remained elusive: Hadronic characteristics are not explicit properties of the QCD Lagrangian and perturbative QCD, so successful in the large transverse momentum domain, is not applicable at large distances. In this article, we shall examine how this daunting obstacle is overcome in holographic QCD with the introduction of a superconformal symmetry in anti de Sitter (AdS) space which is responsible for confinement and the introduction of a mass scale within the superconformal group. When mapped to light-front coordinates in physical spacetime, this approach incorporates supersymmetric relations between the Regge trajectories of meson, baryon and tetraquark states which can be visualized in terms of specific S U (3) C color representations of quarks. We will also briefly discuss here the implications of holographic models for QCD color transparency in view of the present experimental interest. [ABSTRACT FROM AUTHOR]

We study the hadronic coupling constants in the two-body strong decays of the fully-charm tetraquark states with the J PC = 0 + + , 1 + - , and 2 + + via the QCD sum rules based on rigorous quark-hadron duality. Then we obtain the hadronic coupling constants and partial decay widths therefore total decay widths, which support assigning the X(6552) as the first radial excitation of the scalar tetraquark state. And other predictions can be used to diagnose exotic states in the future. [ABSTRACT FROM AUTHOR]

Motivated by the intriguing discovery of X (6900) by the LHCb collaboration, we undertake a comprehensive study of the s s ¯ s s ¯ tetraquark system with positive parity, employing the Gaussian expansion within the chiral quark model method. We consider two structures, the diquark–antidiquark ( s s - s ¯ s ¯ ) structure and meson–meson ( s s ¯ - s s ¯ ) structure, covering all conceivable color and spin configurations. Despite the absence of bound states in our calculations, we have identified potential resonant states with J P = 0 + , namely, R (0 , 2150) and R (0 , 2915) , as well as a resonant state with J P = 1 + , denoted as R (1 , 2950) , and a resonant state with J P = 2 + , denoted as R (2 , 2850) , utilizing the real-scaling method. By comparing their energies and widths, we suggest that R (0 , 2915) and R (1 , 2950) may share characteristics with X (6900) , while R (0 , 2150) could be a promising candidate for the experimental state f 0 (2100) . We strongly advocate for experimental investigations to shed light on the existence and properties of these resonant states. [ABSTRACT FROM AUTHOR]

In this paper, we employ gauge/gravity duality to investigate the string breaking and melting of doubly-heavy tetraquark that includes two heavy quarks and two light antiquarks in a holographic model at finite temperature. Firstly, four different configurations of QQ q ¯ q ¯ are studied at different separation distances of the heavy quarks at finite temperatures. At high temperature, QQ q ¯ q ¯ will melt at certain distances and the screening distance has been given for different temperatures. As the temperature continues to increase, some configurations of doubly-heavy tetraquark can not exist. Furthermore, we investigate three decay modes of QQ q ¯ q ¯ and compare the potential energy of QQ q ¯ q ¯ with that of QQq at finite temperature. [ABSTRACT FROM AUTHOR]

We have studied the strong decay properties of the recently observed T c s ¯ 0 a (2900) + + / 0 by considering it as a c u d ¯ s ¯ / c d u ¯ s ¯ fully open-flavor tetraquark state with I (J P) = 1 (0 +) . In the framework of QCD sum rules, we have calculated the three-point correlation functions of the two-body strong decay processes T c s ¯ 0 a (2900) + + → D s + π + , D + K + , D s ∗ + ρ + and D s 1 + π + . The full width of T c s ¯ 0 a (2900) + + / 0 is obtained as 161.7 ± 94.8 MeV, which is consistent with the experimental observation. We predict the relative branching ratios as Γ (T → D s π) : Γ (T → D K) : Γ (T → D s ∗ ρ) : Γ (T → D s 1 π) ≈ 1.00 : 1.10 : 0.04 : 0.43 , implying that the main decay modes of T c s ¯ 0 a (2900) + + / 0 state are D s π and DK channels in our calculations. However, the P-wave decay mode D s 1 π is also comparable and important by including the uncertainties. To further identify the nature of T c s ¯ 0 a (2900) + + / 0 , we suggest confirming them in the DK and D s π final states, and measuring the above ratios in future experiments. [ABSTRACT FROM AUTHOR]

In this paper, we tentatively assign the Y (4 2 3 0) as the vector tetraquark state with a relative P-wave between the scalar diquark pair, and explore the three-body strong decays Y (4 2 3 0) → D ̄ ∗ − D ∗ 0 π + , D ̄ ∗ − D 0 π + , J ∕ ψ π + π − and J ∕ ψ K + K − with the light-cone QCD sum rules by assuming contact four-meson coupling constants. The resulting partial decay widths are too small to account for the experimental data, and we expect those decays take place through an intermediate meson. We can search for the intermediate states and precisely measure the branching fractions to diagnose the nature of the Y states. [ABSTRACT FROM AUTHOR]

Various models of tetraquark generation in the reaction are considered. The predictions for corresponding inclusive spectra were evaluated at the energies 32 and 250 GeV. [ABSTRACT FROM AUTHOR]

We explore the first radial excitation X 4c ∗ of the fully charmed diquark-antidiquark state X 4c = c c c ¯ c ¯ built of axial-vector components, and the hadronic molecule M = χ c 1 χ c 1 . The masses and current couplings of these scalar states are calculated in the context of the QCD two-point sum rule approach. The full widths of X 4c ∗ and M are evaluated by taking into account their kinematically allowed decay channels. We find partial widths of these processes using the strong couplings g i ∗ and G i (∗) at the X 4c ∗ (M )-conventional mesons vertices computed by means of the QCD three-point sum rule method. The predictions obtained for the parameters m = (7235 ± 75) MeV , Γ = (144 ± 18) MeV and m ~ = (7180 ± 120) MeV , Γ ~ = (169 ± 21) MeV of these structures, are compared with the experimental data of the CMS and ATLAS Collaborations. In accordance to these results, within existing errors of measurements and uncertainties of the theoretical calculations, both the excited tetraquark and hadronic molecule may be considered as candidates to the resonance X(7300). Detailed analysis, however, demonstrates that the preferable model for X(7300) is an admixture of the molecule M and sizeable part of X 4c ∗ . [ABSTRACT FROM AUTHOR]

Inspired by the observation of the X(6900) by LHCb and the X(6600) (with mass 6552 ± 10 ± 12 MeV) recently by CMS and ATLAS experiments of the LHC in the di- J / Ψ invariant mass spectrum, we systemically study masses of all ground-state configurations of the hidden heavy-flavor tetraquarks q 1 Q 2 q ¯ 3 Q ¯ 4 and Q 1 Q 2 Q ¯ 3 Q ¯ 4 (Q = c , b ; q = u , d , s) containing two and four heavy quarks in the MIT bag model with chromomagnetic interaction and enhanced binding energy. Considering color-spin mixing due to chromomagnetic interaction, our mass computation indicates that the observed X(6600) is likely to be the 0 + + ground states of hidden-charm tetraquark c c c ¯ c ¯ with computed masses 6572 MeV, which has a 0 + + color partner around 6469 MeV. The fully bottom system of tetraquark b b b ¯ b ¯ has masses of 19685 MeV and 19717 MeV for the 0 + + ground states. Further calculation of the tetraquark systems s c s ¯ c ¯ , s b s ¯ b ¯ , c b c ¯ b ¯ , n c n ¯ c ¯ and n b n ¯ b ¯ shows that Z c (4200) is a 1 + - state of tetraquark n c n ¯ c ¯ and Z(4020) is a 1 + - state of tetraquark n c n ¯ c ¯ with a mass of 4079 MeV. All of these tetraquarks are above their lowest thresholds of two mesons and unstable against the strong decays. [ABSTRACT FROM AUTHOR]

Currently, flavour-cryptoexotic tetraquarks form the most common sort of all experimentally established exotic multiquark hadrons. This note points out a few promising concepts that should help improve theoretical (but, for several reasons, not quite straightforward) analyses of this kind of states; among others, their scope of application encompasses the strong interactions in the limit of (arbitrarily) large numbers of colours, and equally analytical and nonperturbative approaches to multiquark states. [ABSTRACT FROM AUTHOR]

The lowest-lying charmonium-like tetraquarks c c ¯ q q ¯ (q = u , d) and c c ¯ s s ¯ , with spin-parity J P = 0 + , 1 + and 2 + , and isospin I = 0 and 1, are systematically investigated within the theoretical framework of complex-scaling range for a chiral quark model that has already been successfully applied in former studies of various tetra- and penta-quark systems. A four-body S-wave configuration which includes meson–meson, diquark–antidiquark and K-type arrangements of quarks, along with all possible color wave functions, is comprehensively considered. Several narrow resonances are obtained in each tetraquark channel when a fully coupled-channel computation is performed. We tentatively assign theoretical states to experimentally reported charmonium-like signals such as X(3872), Z c (3900) , X(3960), X(4350), X(4685) and X(4700). They can be well identified as hadronic molecules; however, other exotic components which involve, for instance, hidden-color channels or diquark–antidiquark structures play a considerable role. Meanwhile, two resonances are obtained at 4.04 GeV and 4.14 GeV which may be compatible with experimental data in the energy interval 4.0–4.2 GeV. Furthermore, the X(3940) and X(4630) may be identified as color compact tetraquark resonances. Finally, we also find few resonance states in the energy interval from 4.5 to 5.0 GeV, which would be awaiting for discovery in future experiments. [ABSTRACT FROM AUTHOR]

According to the classification of the quark model, the hadrons going beyond three-quark baryon and quark-antiquark meson pictures are called exotic hadrons. Many new hadrons have been observed since 2003, some of which exhibit exotic behaviors. There are a lot of excellent review articles on exotic hadrons available so far; the present article tries to focus on the recent experimental and theoretical progress on the exotic states from the perspective of the quark model. Although lattice quantum chromodynamics may give the final answer of the problem, the phenomenological models are still powerful tools to explore the exotic states and to provide insight on the phenomenology of hadrons. The spatial and color structures of multiquark states and the channel coupling calculation are emphasized through reviewing some bound states, molecular and color structure resonances. Finally, the unquench effects of some exotic states are reviewed. With the accumulation of experimental data on multiquark states and inspiration of underlying theory developments, more reasonable phenomenological models incorporating multi-body interactions and high Fock components to unify the description of normal hadrons and exotic hadrons are expectable. [ABSTRACT FROM AUTHOR]

Inspired by the fully heavy tetraquark states reported by the LHCb, ATLAS and CMS Collaborations, we perform a systematical investigation of the low-lying fully heavy pentaquark systems composed of charm and bottom quarks (anti-quark) in the chiral quark model. With the help of the channel-coupling, we obtain several fully heavy pentaquark candidates, which are c c c c b ¯ and b b b b c ¯ systems with J P = 1 / 2 - and 3 / 2 - , c c c b c ¯ , b b b c b ¯ , c c c b b ¯ and b b b c c ¯ systems with J P = 5 / 2 - . The binding energies of these states are all below 10 MeV and the root mean square (RMS) are around 1.8 fm, which indicates that these states are likely to be molecular states. These predicted exotic states may provide new ideas for experimental searches and we expect more experimental and theoretical researches to study and understand the fully heavy states in future. [ABSTRACT FROM AUTHOR]

We investigated the four-quark systems with quark structures of c s c ¯ s ¯ , c q c ¯ s ¯ , b s b ¯ s ¯ , and b q b ¯ s ¯ in the framework of the non-relativistic quark model, motivated by the recent observation of exotic resonances X(4140), X(4274), X(4350), X(4500), and X(4700) reported by several experiment collaborations. The colour antitriplet-triplet configuration of diquark-antidiquark combinations with all conceivable quantum numbers have been used to calculate their masses. The results reveal that if the colour structure of the diquark-antidiquark configuration is 3 ¯ c ⊗ 3 , the tetraquarks structures may occur otherwise may observed as resonance. The X(4274) state, can be defined as the J PC = 2 + + tetraquark state, while the X(4140) state can be regarded as the J PC = 1 + + tetraquark state in this calculation. When radial excitation is considered, X(4700) may be explained as a 2 S radial excited tetraquark state with J PC = 0 + + . The orbitally excited states Y(4626), Y(4630) and Y(4660) can be explained as P-wave tetraquark with quantum number 1 - - . The masses of [ b s b ¯ s ¯ ] and [ b q b ¯ s ¯ ] are found to be in the range between 10.5 and 11.5 GeV and are very close to two-meson thresholds. [ABSTRACT FROM AUTHOR]

J pc = 0 + + and 2 + + states of all charm tetraquark ( [ c c ] [ c ¯ c ¯ ] ) are investigated in the framework of non-relativistic QCD using diquark-antidiquark coulomb plus power potential of the type V d d ¯ = k s α s r + A r ν with power index ν varying from 0.1 to 2. We have included the spin hyperfine interaction to obtain masses of J pc = 0 + + and 2 + + states of all charm tetraquark. We have computed branching ratios and decay widths of the main, hidden and open charm channels of tetraquark state with the help of the potential model parameters, masses and the respective radial wave function obtained by our non-relativistic quark model. Our theoretical predictions of the masses as well as the branching ratios and decay widths at power index ν =1 are found to be in good accordance with other available theoretical predictions. [ABSTRACT FROM AUTHOR]

We study the S-wave mass spectra of flavor exotic triply-heavy tetraquark states c c c ¯ q ¯ , c c b ¯ q ¯ , b b c ¯ q ¯ and b b b ¯ q ¯ . We adopt a diquark–antidiquark scheme to solve Schrödinger equation. The calculations are carried out in a nonrelativistic quark model with a color interaction described by a potential computed in AdS/QCD. The AdS/QCD potential model consists of a central potential which reflects short distance and large distance behaviour of QCD, spin dependent term for hyperfine splitting and a constant term. We find stable state candidates in the c c c ¯ q ¯ sector whereas in the c c b ¯ q ¯ , b b c ¯ q ¯ and b b b ¯ q ¯ sectors all the states lie above corresponding S-wave meson-meson thresholds. [ABSTRACT FROM AUTHOR]

Inspired by recent progresses in observations of the fully charmed tetraquark states by LHCb, CMS, and ATLAS collaborations, we perform a systematic study of the ground states and the first radial excitations of the S- and P-wave cc c ¯ c ¯ system. Their mass spectra, root mean square (r.m.s.) radii and radial density distributions are studied with the relativized quark model. The calculations show that there is no stable bound states for the fully charmed tetraquark states, and the r.m.s. radii of these tetraquark states are smaller than 1 fm. Our results support assigning X(6600) structure, M X (6600) = 6552 ± 10 ± 12 MeV, as one of the 0 + + (1S) and 2 + + (1S) states or their mixtures. Another structure also named as X(6600) by CMS Collaboration, M X (6600) = 6.62 ± 0. 03 - 0.01 + 0.02 GeV, may arise from the lowest 1P states with J PC = 0 - + , 1 - + , and 2 - + . The possible assignments for X(6900) include the 0 + + (2S), 2 + + (2S) states, and the highest 1P state with J PC = 0 - + . As for X(7200), it can be interpreted as one of the highest 2P states with J PC = 0 - + , 1 - + , and 2 - + , and the 3S states can not be completely excluded from the candidates. [ABSTRACT FROM AUTHOR]

In this research, we tentatively assign the T c s ̄ (2 9 0 0) as the A Ā -type tetraquark state, and study the mass spectrum of the tetraquark states with strange and doubly strange, which have the spin-parity J P = 0 + , 1 + and 2 + , in the framework of the QCD sum rules in details, where the A denotes the axialvector-diquark state. The predicted mass M = 2. 9 2 ± 0. 1 2 GeV is consistent with the experimental values M = 2. 8 9 2 ± 0. 0 1 4 ± 0. 0 1 5 GeV and 2. 9 2 1 ± 0. 0 1 7 ± 0. 0 2 0 GeV from the LHCb collaboration and supports assigning the T c s ̄ (2 9 0 0) to be the A Ā -type scalar c s ̄ q q ̄ tetraquark state. The predictions for other tetraquark states can be confronted to the experimental data in the future to diagnose the nature of the fully open flavor exotic states. [ABSTRACT FROM AUTHOR]

Motivated by the recent observation of the tetraquark T cc + , we investigate the magnetic dipole moments of the possible single and double strange partners, T QQ q ¯ s ¯ and T QQ s ¯ s ¯ , with the spin-parity JP = 1+ by means of the QCD light-cone sum rules. To this end, we model these states as diquark-antidiquark states with different organizations and interpolating currents. The results of magnetic dipole moments obtained using different diquark-antidiquark structures differ from each other, considerably. The magnetic dipole moment is the leading-order response of a bound system to a soft external magnetic field. Therefore, it provides an excellent platform for investigation of the inner structures of hadrons governed by the quark-gluon dynamics of QCD. [ABSTRACT FROM AUTHOR]

In recent years, many tetraquarks and pentaquarks have been discovered by various experimental groups and X (3 8 7 2) , Z c (3 9 0 0) , X (4 4 3 0) , P c + (4 3 1 2) , P c + (4 4 5 7) are some of the interesting observed tetraquark and pentaquark states. The Regge trajectories of some such states are studied in view of the flux tube model of hadrons with finite quark masses. The effect of flux tube (or string) length variation on the Regge trajectories of these states is analyzed in detail. It is observed that for a fixed angular momentum, the string length has a constant value. Some other states are also proposed and the results obtained are then compared with the studies by others. Our findings correspond rather well with those of other researchers and with those of the experiment. [ABSTRACT FROM AUTHOR]

The production mechanism of multiquark exotic hadrons in high energy multiproduction processes lies in the structure of the relevant exotic hadrons as well as in some important aspects of high energy scattering, such as multi-parton interactions, underlying events, etc. At mass pole around 2900 MeV, a family of open charm tetraquarks,  T c s s and  T c s ¯ s, are observed in B decay. They are also suitable for study in multiproduction processes to obtain more information on their structure. If these resonances are produced as compact four-quark states, one can predict the production properties based on the similarities in their production mechanism to those of  Ξ c ,  Σ c , and  Λ c . Physics implies that the colour and baryon number fluctuations of the preconfinement system in high energy scattering can enhance both the baryon and four-quark state production rates via 'diquark fragmentation'. We calculate the production properties of the tetraquark family  T c s s and  T c s ¯ s at LHC energy for the forthcoming LHC measurements. [ABSTRACT FROM AUTHOR]

In this work, we propose to search for the exotic doubly charmed meson T cc + and its analog T c c s ¯ + in B c + decays, which provide a good environment for the formation of the exotic state containing double charm quarks. Within the molecular scheme, the production of T cc + and T c c s ¯ + through various rescattering processes with different intermediate states are investigated. For the moderate values of model parameters, the branching ratios of B c + decaying into T cc + D ¯ 0 , T cc + D ¯ ∗ 0 , T c c s ¯ + D ¯ 0 and T c c s ¯ + D ¯ ∗ 0 are estimated to be of the order of 10 - 7 , 10 - 5 , 10 - 6 and 10 - 4 , respectively, which may be tested by future experiments. [ABSTRACT FROM AUTHOR]

Discoveries of tetraquarks not only enrich the hadronic spectrum but also provide more platforms to understand quantum chromodynamics. We study the production processes of hidden-charm and open-charm tetraquarks in B decays by analyzing their topological amplitudes. Relations between different channels are found, which confront tests by experiments to probe the nature of the tetraquarks. Furthermore, promising channels to find more tetraquarks are proposed. [ABSTRACT FROM AUTHOR]

Spectroscopic parameters and widths of the fully open-flavor axial-vector and pseudoscalar tetraquarks X AV and X PS with content [ u d ] [ c ¯ s ¯ ] are calculated by means of the QCD sum rule methods. Masses and current couplings of X AV and X PS are found using two-point sum rule computations performed by taking into account various vacuum condensates up to dimension 10. The full width of the axial-vector state X AV is evaluated by including into analysis S-wave decay modes X AV → D ∗ (2010) - K + , D ¯ ∗ (2007) 0 K 0 , D - K ∗ (892) + , and D ¯ 0 K ∗ (892) 0 . In the case of X PS , we consider S-wave decay X PS → D ¯ 0 ∗ (2300) 0 K 0 , and P-wave processes X PS → D - K ∗ (892) + and X PS → D ¯ 0 K ∗ (892) 0 . To determine partial widths of these decay modes, we employ the QCD light-cone sum rule method and soft-meson approximation, which are necessary to estimate strong couplings at tetraquark–meson–meson vertices X AV D - D ∗ (2010) - K + , etc. Our predictions for the mass m AV = (2800 ± 75) MeV and width Γ AV = (58 ± 10) MeV of the tetraquark X AV , as well as results m PS = (3000 ± 60) MeV and Γ PS = (65 ± 12) MeV for the same parameters of X PS may be useful in future experimental studies of multiquark hadrons. [ABSTRACT FROM AUTHOR]

In this paper, the new analytic–exact energy eigenvalues and eigenfunctions are obtained in the fractional forms by using the extended Nikiforov–Uvarov approach in which the heavy diquark systems are described. We have recalculated the mass spectra and fractional radial wave of heavy tetraquarks. The mass spectra are compared to the experimental data. The present results show a good agreement with the experimental data and are improved in comparison with other studies. We conclude that the fractional models play a good role in the heavy tetraquark masses. [ABSTRACT FROM AUTHOR]

The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark states X (2900) and T c c + (3875) as well as the hidden heavy flavor multiquark states X (6900), P c s (4459) 0 , Z c s (3985) − , Z c s (4000) + , and Z c s (4220) + . We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-Abelian SU (3) gauge interaction of the Quantum Chromodynamics in the low-energy region. [ABSTRACT FROM AUTHOR]

Since in recent years most of the heavy tetraquarks are discovered by Belle, LHCb, BESIII, etc., it motivated us to study these exotic hadrons. To the extent of our knowledge about the mass characteristics of heavy tetraquarks, we utilize the spinless relativistic Bethe–Salpeter equation by applying the Cornell potential in order to calculate the eigenvalue and mass of heavy tetraquarks. For this purpose, we present an ansatz solution to obtained Schrödinger-like equation to calculate the ground-state energy of diquarks and tetraquarks. Eventually, we compare our obtained predictions for heavy tetraquark masses with available experimental and theoretical data. [ABSTRACT FROM AUTHOR]

Motivated by the intriguing discovery of X(6900) by the LHCb collaboration, we undertake a comprehensive study of the ss¯ss¯ tetraquark system with positive parity, employing the Gaussian expansion within the chiral quark model method. We consider two structures, the diquark–antidiquark (ss-s¯s¯) structure and meson–meson (ss¯-ss¯) structure, covering all conceivable color and spin configurations. Despite the absence of bound states in our calculations, we have identified potential resonant states with JP=0+, namely, R(0,2150) and R(0,2915), as well as a resonant state with JP=1+, denoted as R(1,2950), and a resonant state with JP=2+, denoted as R(2,2850), utilizing the real-scaling method. By comparing their energies and widths, we suggest that R(0,2915) and R(1,2950) may share characteristics with X(6900), while R(0,2150) could be a promising candidate for the experimental state f0(2100). We strongly advocate for experimental investigations to shed light on the existence and properties of these resonant states.

In this work, we study the D D ¯ , DD, D D ¯ s , D D s , D s D ¯ s and D s D s tetraquark molecular states with the J PC = 0 + + via the QCD sum rules. The prediction M D s D ¯ s = 3.98 ± 0.10 GeV is in very good agreement with the experimental value M X (3960) = 3956 ± 5 ± 10 MeV from the LHCb collaboration and supports assigning the X(3960) as the D s + D s - molecular state with the J PC = 0 + + . We take account of our previous works on the four-quark states consisting of two color-neutral clusters and acquire the mass spectrum of the ground state hidden-charm and doubly-charm tetraquark molecular states. [ABSTRACT FROM AUTHOR]

Masses of the ground and excited (1P, 2S, 1D, 2P, 3S) states of the fully heavy tetraquarks, composed of charm (c) and bottom (b) quarks and antiquarks, are calculated in the diquark–antidiquark picture within the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The quasipotentials of the quark–quark and diquark–antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Relativistic effects are consistently taken into account. A tetraquark is considered a bound state of a diquark and an antidiquark. The finite size of the diquark is taken into account, using the form factors of the diquark–gluon interaction. It is shown that most of the investigated states of tetraquarks lie above the decay thresholds into a meson pair; as a result, they can be observed only as broad resonances. The narrow state X(6900) recently discovered in the di- J / ψ production spectrum by the LHCb, CMS and ATLAS Collaborations corresponds to an excited state of the fully charmed tetraquark. Other recently discovered exotic heavy resonances, X(6200), X(6400), X(6600), X(7200), and X(7300), can also be interpreted as the different excitations of the fully charmed tetraquark. [ABSTRACT FROM AUTHOR]

In present work, spectrum of the S-wave fully-heavy tetraquark states Q Q Q ¯ Q ¯ ( Q = c , b ), i.e., c c c ¯ c ¯ , b b b ¯ b ¯ , c c b ¯ b ¯ / b b c ¯ c ¯ , b c c ¯ c ¯ / c c b ¯ c ¯ , b b c ¯ b ¯ / c b b ¯ b ¯ , and b c b ¯ c ¯ are systematically investigated within a nonrelativistic constituent quark model, in which the instanton-induced and one-gluon-exchange interactions are taken into account as the residual spin-dependent hyperfine interaction. Our results show that the states with c c c ¯ c ¯ and b b b ¯ b ¯ components could be located around 6500 MeV and 19,200 MeV, respectively. Based on our calculations, the new X(6900) state observed by LHCb may be not a ground c c c ¯ c ¯ tetraquark state, while it could be an orbitally or radially excited state of c c c ¯ c ¯ system. On the other hand, the recently reported X(6600) state by CMS and ATLAS can be explained as a ground c c c ¯ c ¯ tetraquark state with spin-parity J PC = 0 + + . [ABSTRACT FROM AUTHOR]

Recently, the tetraquark mixing framework has been proposed as a possible structure for the two light-meson nonets in the J P = 0 + channel, the light nonet composed of a 0 (980) , K 0 ∗ (700) , f 0 (500) , f 0 (980) , and the heavy nonet of a 0 (1450) , K 0 ∗ (1430) , f 0 (1370) , f 0 (1500) . Among various signatures, we report in this work that their partial decay widths collected from various experimental data in Particle Data Group (PDG) can support this mixing scheme also. In particular, we demonstrate that the couplings of the light nonet to two pseudoscalar mesons estimated from the partial widths are consistently stronger than those of the heavy nonet. This consistent feature agrees qualitatively well with the predictions from the tetraquark mixing framework and, therefore, provides supporting evidence for the tetraquark mixing. [ABSTRACT FROM AUTHOR]

In this paper, we apply the method of QCD sum rules to study the doubly heavy tetraquark states Q Q q ̄ n ̄ with spin-parity J P = 1 + and strangeness S = 0 , − 1 using careful estimates of the Borel and threshold parameters involved. Masses of the doubly bottom and charmed tetraquarks with isospin I = 0 , 1 / 2 , 1 are computed precisely via taking into account multifarious condensates up to dimension 10. Compared with the two-heavy meson thresholds, we find that all nonstrange doubly-bottom tetraquarks and a doubly-charmed tetraquarks associated with J 3 with J P = 1 + are stable against strong decay into two bottom mesons while a doubly-charmed tetraquark associated with current J 2 is unstable against strong decay. By the way, weak decay widths of the doubly bottom tetraquarks are also given. [ABSTRACT FROM AUTHOR]

During the past 40 years, the production of pairs of J ∕ ψ mesons in high-energy hadron collisions has been studied by several experiments. Despite the experimental and theoretical efforts, the origin of the process and the relative weight of different production mechanisms remain unknown. Depending on the energy scale, the double J ∕ ψ production can be described by single- and/or double-parton scattering sub-processes and gluon–gluon fusion or quark–antiquark annihilation mechanisms. The process can also be related to the hypothesis of the intrinsic charm of hadrons and the existence of exotic tetraquark states which were predicted by various theoretical models and have recently been observed by the LHCb experiment. To study dimuon pair production, the COMPASS experiment at CERN uses a 190 GeV/ c negative pion beam impinging on different nuclear targets. First preliminary COMPASS results on J ∕ ψ pair production will be presented. The search for possible signals from exotic resonances and the study of double J ∕ ψ production mechanisms will be discussed. [ABSTRACT FROM AUTHOR]

The three pentaquark states, P c (4312) , P c (4440) and P c (4457) , discovered by the LHCb Collaboration in 2019, can be arranged into a complete heavy quark spin symmetry multiplet of hadronic molecules of D ¯ (∗) Σ c (∗) . In the heavy quark mass limit, the Σ c (∗) baryons can be related to the doubly charmed tetraquark states of isospin 1, i.e., T c ¯ c ¯ (∗) ( T c ¯ c ¯ 0 , T c ¯ c ¯ 1 , T c ¯ c ¯ 2 ), via heavy antiquark diquark symmetry, which dictates that the D ¯ (∗) Σ c (∗) interactions are the same as the D ¯ (∗) T c ¯ c ¯ (∗) interactions up to heavy antiquark diquark symmetry breakings. In this work, we employ the contact-range effective field theory to systematically study the D ¯ (∗) T c ¯ c ¯ (∗) systems, and we show the existence of a complete heavy quark spin symmetry multiplet of hadronic molecules composed of a doubly charmed tetraquark state and a charmed meson. These are a new kind of hadronic molecules and, if discovered, can lead to a better understanding of the many exotic hadrons discovered so far. In addition, we summarise the triply charmed hexaquark states formed by different combinations of hadrons. In particular, we show that Ω ¯ ccc p system can bind by the Coulomb force, which is analogous to a hydrogenlike atom. [ABSTRACT FROM AUTHOR]

The first measurements of femtoscopic correlations with the particle pair combinations π ± K S 0 in pp collisions at s = 13 TeV at the Large Hadron Collider (LHC) are reported by the ALICE experiment. Using the femtoscopic approach, it is shown that it is possible to study the elusive K 0 ⁎ (700) particle that has been considered a tetraquark candidate for over forty years. Source and final-state interaction parameters are extracted by fitting a model assuming a Gaussian source to the experimentally measured two-particle correlation functions. The final-state interaction in the π ± K S 0 system is modeled through a resonant scattering amplitude, defined in terms of a mass and a coupling parameter, The extracted mass and Breit–Wigner width, derived from the coupling parameter, of the final-state interaction are found to be consistent with previous measurements of the K 0 ⁎ (700). The small value and increase of the correlation strength with increasing source size support the hypothesis that the K 0 ⁎ (700) is a four-quark state, i.e. a tetraquark state of the form (q 1 , q 2 ‾ , q 3 , q 3 ‾) in which q 1 , q 2 and q 3 indicate the flavor of the valence quarks of the π and K S 0. This latter trend is also confirmed via a simple geometric model that assumes a tetraquark structure of the K 0 ⁎ (700) resonance. [ABSTRACT FROM AUTHOR]

The mass and width of the tensor tetraquark T = b b c ‾ c ‾ with spin-parity J P = 2 + are calculated in the context of the QCD sum rule method. The tetraquark T is modeled as a diquark-antidiquark state built of components b T C γ μ b and c ‾ γ ν C c ‾ T with C being the charge conjugation matrix. The mass m = (12.795 ± 0.095) GeV of the exotic tensor meson T is found by means of the two-point sum rule approach. Its full width Γ is evaluated by considering processes T → B c − B c − , B c − B c ⁎ − , and B c ⁎ − B c ⁎ −. Partial widths of these decays are computed by means of the three-point sum rule approach which is used to determine the strong couplings at relevant tetraquark-meson-meson vertices. Predictions obtained for the width Γ T = 55.5 − 9.9 + 10.6 MeV , as well as the mass of the tetraquark T can be useful in investigations of fully heavy four-quark mesons. [ABSTRACT FROM AUTHOR]

We suppose that there exist three vector hidden-charm tetraquark states with the J P C = 1 − − at the energy about 4.5 GeV , and investigate the two-body strong decays systematically. We obtain thirty QCD sum rules for the hadronic coupling constants based on rigorous quark-hadron duality, then obtain the partial decay widths, therefore the total widths approximately, which are compatible with the experimental data of the Y (4500) from the BESIII collaboration. The Y (4500) may be one vector tetraquark state having three main Fock components, or consists of three different vector tetraquark states. We can search for the typical decays Y → D ¯ 1 0 D 0 − D ¯ 0 D 1 0 2 , D ¯ 1 − D + − D ¯ − D 1 + 2 , D ¯ 0 0 D ⁎ 0 − D ¯ ⁎ 0 D 0 0 2 , D ¯ 0 − D ⁎ + − D ¯ ⁎ − D 0 + 2 , η c ω , J / ψ ω to diagnose the nature of the Y (4500). [ABSTRACT FROM AUTHOR]