Implications of heavy quark-diquark symmetry for excited doubly heavy baryons and tetraquarks
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Mehen, Thomas↗
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Tetraquarks made of sufficiently unequal-mass heavy quarks are bound in QCD
Tetraquarks, bound states composed of two quarks and two antiquarks, have been the subject of intense study but are challenging to understand from first principles. We apply variational and Green’s function Monte Carlo methods to compute tetraquark ground-state energies in potential nonrelativistic QCD using a wide range of color and spatial wave functions. We find no evidence for bound tetraquarks composed of equal-mass quarks and antiquarks. Conversely, we find clear evidence for the existence of bound tetraquarks for sufficiently unequal quark/antiquark mass ratios at all overall mass scales where our effective theory results are applicable. We predict the critical mass ratios for bound state formation and study tetraquark bound states’ spatial and color structure at leading order and next-to-leading order in potential nonrelativistic QCD. Published by the American Physical Society 2024
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
b ¯ b ¯ u d and b ¯ b ¯ u s tetraquarks from lattice QCD using symmetric correlation matrices with both local and scattering interpolating operators
We study the b ¯ b ¯ u d tetraquark with quantum numbers I ( J P ) = 0 ( 1 + ) as well as the b ¯ b ¯ u s tetraquark with quantum numbers J P = 1 + using lattice QCD. We improve on existing work by including both local and scattering interpolating operators on both sides of the correlation functions and use symmetric correlation matrices. This allows not only a reliable determination of the energies of QCD-stable tetraquark ground states, but also of low-lying excited states, which are meson-meson scattering states. The latter is particularly important for future finite-volume scattering analyses. Here, we perform chiral and continuum extrapolations of just the ground-state energies, for which finite-volume effects are expected to be small. Our resulting tetraquark binding energies, − 100 ± 10 − 51 + 36 MeV for b ¯ b ¯ u d and − 30 ± 3 − 31 + 11 MeV for b ¯ b ¯ u s , are consistent with other recent lattice-QCD predictions. Published by the American Physical Society 2024
Astronomy & Astrophysics↗
Hidden-charm and bottom tetra- and pentaquarks with strangeness in the hadro-quarkonium and compact tetraquark models
In two recent papers, we used the hadro-quarkonium model to study the properties of hiddencharm and bottom tetraquarks and pentaquarks. Here, we extend the previous results and calculate the masses of heavy-quarkonium-kaon/hyperon systems. We also compute the spectrum of hiddencharm and bottom tetraquarks with strangeness in the compact tetraquark (diquark-antidiquark) model. If heavy-light exotic systems with non-null strangeness content were to be observed experimentally, it might be possible to distinguish among the large variety of available theoretical pictures for tetra- and pentaquark states and, possibly, rule out those which are not compatible with the data.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Tetraquarks in the Born-Oppenheimer approximation
The conventional loosely bound molecule interpretation of the X(3872) is not compatible with the recent LHCb experimental measurement of the ratio of branching fractions $\mathcal{R}$ = Br(X → ψ′γ)/Br(X → ψγ). We systematically determine the entire tetraquark spectrum for J = 0, 1, 2 and refine the calculation of $\mathcal{R}$ in an improved Born-Oppenheimer description of the X(3872) compact tetraquark. This refinement yields a significantly better agreement with experimental data on $\mathcal{R}$ and on the spectroscopy of the states themselves. Extending the diquark-antidiquark paradigm to encompass tetraquarks that are linear super-positions of open charm singlets and color octets, we discover that these exotic resonances manifest as compact shallow bound states of quarks in color force potentials.
Effective Field Theories of QCD↗
Tetraquark operators in lattice QCD and exotic flavour states in the charm sector
We present a general class of operators resembling compact tetraquarks which have a range of colour-flavour-spin structures, transform irreducibly under the symmetries of the lattice and respect other relevant symmetries. These constructions are demonstrated in lattice QCD calculations with light quarks corresponding to m π = 391 MeV. Using the distillation framework, correlation functions involving large bases of meson-meson and tetraquark operators are computed in the isospin-1 hidden-charm and doubly-charmed sectors, and finite-volume spectra are extracted with the variational method. We find the spectra are insensitive to the addition of tetraquark operators to the bases of meson-meson operators. For the first time, through using diverse bases of meson-meson operators, the multiple energy levels associated with meson-meson levels which would be degenerate in the non-interacting limit are extracted reliably. The number of energy levels in each spectrum is found to be equal to the number of expected non-interacting meson-meson levels in the energy region considered and the majority of energies lie close to the non-interacting levels. Furthermore, there is no strong indication for any bound state or narrow resonance in the channels we study.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Tetraquarks from intrinsic heavy quarks
A number of new tetraquark candidate states containing from one to four charm or anticharm quarks have been observed recently. Many of these new states have been discovered at the LHC. The production of these states via intrinsic charm in the proton is investigated. The tetraquark masses obtained in this approach, while dependent on the internal transverse momenta of the partons in the state, are shown to agree well with the measured masses. These calculations can provide some insight into the nature of the tetraquark candidates, whether as a bound meson pair or as a looser configuration of four individual partons. The kinematic distributions of these states as a function of rapidity and transverse momentum are also studied. The possible cross sections for these states are finally considered, with a comparison to the 𝑋(3872) 𝑝 𝑇 distributions from 𝑝 +𝑝 collisions at $\sqrt{s}$ =13 TeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Stable, Doubly Heavy Tetraquark Mesons [Slides]
Heavy-quark symmetry implies stable heavy tetraquark mesons $Q_iQ_j \overline{q}_k\overline{q}_l$ In the limit of very heavy quarks Q, novel narrow doubly heavy tetraquark states must exist. The lightest double-beauty states composed of $bb\overline{u}\overline{d}$, $bb\overline{u}\overline{s}$, and $bb\overline{d}\overline{s}$ will be stable against strong decays. Heavier $bb\overline{q}_k \bar{q}_l$ states, double-charm states $cc\overline{q}_k \overline{q}_l$ , mixed $bc\overline{q}_k\overline{q}_l$ states, will dissociate into pairs of heavy-light mesons. Observing a weakly decaying double-beauty state would establish the existence of tetraquarks and illuminate the role of heavy color-antitriplet diquarks as hadron constituents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Stable Tetraquarks [Slides]
Heavy-quark symmetry implies stable heavy tetraquark mesons $Q_iQ_j\overline{q}_k\overline{q}_l$ In the limit of very heavy quarks Q, novel narrow doubly heavy tetraquark states (DHTQ) must exist. HQS relates DHTQ mass to masses of a doubly heavy baryon, heavy-light baryon, and heavy-light meson. The lightest double-beauty states composed of $bb \overline{u} \overline{d}$, $bb \overline{u}\overline{s}$, and $bb \overline{d} \overline{s}$ will likely be stable against strong decays. Heavier $bb\overline{q}_k \overline{q}_l$ states, $cc \overline{q}_k \overline{q}_l$ states, and mixed $bc \overline{q}_k \overline{q}_l$ states, will likely dissociate into pairs of heavy-light mesons. Some might be seen as \double- avor" resonances near threshold. Observing a weakly decaying double-beauty state would establish the existence of tetraquarks and illuminate the role of heavy color-$\overline{3}$ diquarks as hadron constituents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Stable, Doubly Heavy Tetraquark Mesons [Slides]
Heavy-quark symmetry implies stable heavy tetraquark mesons $Q_{i}Q_{j}\overline{q}_{k}\overline{q}_{l}$. in the limit of very heavy quarks Q, novel narrow double heavy tetraquark state (DHTQ) must exist. HQS relates DHTQ mass to masses of a doubly heavy baryon, heavy-light baron, and heavy-light meson. The lightest double-beauty states composed of $bb\overline{ud}$, $bb\overline{us}$, and $bb\overline{ds}$ will likely be stable against strong decays. Heavier $bb\overline{q}_{k}\overline{q}_{l}$ states, $cc\overline{q}_{k}\overline{q}_{l}$ states, and mixed $bc{q}_{k}\overline{q}_{l}$ states, will likely dissociate into pairs of heavy-light mesons. Some might be seen as "double-flavor" resonances near threshold. Observing a weakly decaying double-beauty state would establish the existence of tetraquarks and illuminate the role of heavy color-$\overline{3}$ diquarks as hadron constituents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Melting down a tetraquark: D*D(*) interactions and T c c ( 3875 ) + in a hot environment
We discuss the modification of the properties of the tetraquark-like and its heavy quark spin partner, immersed in a hot bath of pions. We consider these exotic states as purely isoscalar DD* and D*D* S-wave bound states, respectively. Finite temperature effects are incorporated through the D and D* state-of-the-art thermal spectral functions calculated in [G. Montana et al., Phys. Rev. D, 102 (2020) 096020], using the imaginary-time formalism. We find important modifications of the DD* and D*D* scattering amplitudes already for MeV, and show that the hot-bath lineshapes of these tetraquark-like states strongly depend on their Weinberg molecular content. We find that the thermal and spectral functions change more rapidly with temperature for high molecular probabilities P0. For large values of P0, the widths significantly increase with temperature, leading to the melting of these exotic states for temperatures larger than 80 MeV. For small molecular components, the changes in the spectral functions of these states due to temperature become significantly less important. All these results show that any future experimental determination of the D(*)D* scattering amplitudes at finite temperature will provide valuable insights into the molecular content of the and exotics.
Montesinos, V. (ORCID:0000000261862777)↗
Determination of the spin and parity of all-charm tetraquarks
The traditional quark model accounts for the existence of baryons, such as protons and neutrons, which consist of three quarks, as well as mesons, composed of a quark–antiquark pair. Only recently has substantial evidence started to accumulate for exotic states composed of four or five quarks and antiquarks. The exact nature of their internal structure remains uncertain. Here we report the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks, using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018 . The angular analysis techniques developed for the discovery and characterization of the Higgs boson have been applied to the new exotic states. Here we show that the quantum numbers for parity P and charge conjugation C symmetries are found to be +1. The spin J of these exotic states is determined to be consistent with 2ħ, while 0ħ and 1ħ are excluded at 95% and 99% confidence levels, respectively. The J PC = 2 ++ assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks.
Physics↗
Tetraquark Production by Intrinsic Charm
A number of new four-quark states containing from one to four c or ̅c quarks have been observed recently. Many of these new states have been discovered at the LHC. The production of these states via intrinsic charm in the proton is investigated. The tetraquark masses obtained in this approach, agree well with the measured masses. These calculations can provide some insight into the nature of the tetraquark candidates, whether as a bound meson pair or as a looser configuration of four individual partons which can influence their interactions in nuclear medium, such as in heavy-ion collisions. The kinematic distributions of these states as a function of y and pT are also studied. The possible cross sections for these states are also considered.
Vogt, Ramona [Lawrence Livermore National Laborato↗
Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states
The simplest form of the Hyperfine Interaction (HFI) of quarks is a color-spin interaction, sometimes called Fermi-Breit (FB) HFI. For conventional hadrons, this HFI for quark-antiquark (qq) pairs is twice as strong as the same HFI for quark-quark (qq or qq) pairs, but this difference is absorbed into the different HFI constants for mesons and baryons, which are free parameters of the fits. For tetraquarks, however, qqHFI is only half as strong as the qq/qqHFI and both kinds of pairs coexist within the same state. Hence it is worth investigating a model with different fit constants for qq and qq/q pairs. We have investigated 3 models of spin-color HFI for light scalar tetraquarks: 2 models with single constants for both kinds of pairs and one model with different fit constants. The light scalar nonet is chosen because of a lack of other experimentally observed multiplets interpretable as pure exotic states. Since even the nonet contains only 3 particles with distinct masses (i. e. 3 fit points), the constituent quark masses had to be taken from conventional hadron fits obtained in our previous work. The two-constant model did not prove to be a viable alternative to the one-constant models. © 2019 Author(s).
60 APPLIED LIFE SCIENCES↗
Photoproduction of fully charmed tetraquark at electron-ion colliders
In this work, we investigate the inclusive photoproduction of the C -odd, S -wave fully charmed tetraquark at electron-ion colliders within the nonrelativistic QCD (NRQCD) factorization framework, at the lowest order in velocity and α s . The value of the NRQCD long-distance matrix element is estimated from two phenomenological potential models. Our studies reveal that the photoproduction of the 1 + − fully charmed tetraquark may be difficult to observe at HERA and the EicC; nevertheless, its observation prospects at the EIC appear to be bright. Published by the American Physical Society 2024
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Heavy-Quark Symmetry Implies Stable Heavy Tetraquark Mesons Q i Q j q ¯ k q ¯ l
For very heavy quarks Q, relations derived from heavy-quark symmetry predict the existence of novel narrow doubly heavy tetraquark states of the form Q i Q j ¯q k ¯q l (subscripts label flavors), where q designates a light quark. By evaluating finite-mass corrections, we predict that double-beauty states composed of bb¯u¯d, bb¯u¯s, and bb¯d¯s will be stable against strong decays, whereas the double-charm states cc¯q k ¯q l , mixed beauty+charm states bc¯q k ¯q l , and heavier bb¯qk¯ql states will dissociate into pairs of heavy-light mesons. Furthermore, observation of a new double-beauty state through its weak decays would establish the existence of tetraquarks and illuminate the role of heavy color-antitriplet diquarks as hadron constituents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First Observation of a Doubly Charged Tetraquark and Its Neutral Partner
A combined amplitude analysis is performed for the decays $B^0$ → $\overline{D}$ 0 $D_s^+$$π^–$ and $B^+$ → $D^–$$D_s^+$$π^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb –1 . Two new resonant states with masses of 2.908 ± 0.011 ± 0.020 GeV and widths of 0.136 ± 0.023 ± 0.013 GeV are observed, which decay to $D_s^+$$π^+$ and $D_s^+$$π^–$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content [c$\overline{s}$u$\overline{d}$], and the latter state is a neutral tetraquark composed of [c$\overline{s}$$\overline{u}$d] quarks. Both states are found to have spin-parity of 0 + , and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Stable Tetraquarks
For very heavy quarks, relations derived from heavy-quark symmetry imply novel narrow doubly heavy tetraquark states containing two heavy quarks and two light antiquarks. We predict that double-beauty states will be stable against strong decays, whereas the double-charm states and mixed beauty+charm states will dissociate into pairs of heavy-light mesons. Observing a new double-beauty state through its weak decays would establish the existence of tetraquarks and illuminate the role of heavy color-antitriplet diquarks as hadron constituents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗