Hybrid Mesons Research Articles

Some decay modes of the1−+hybrid meson in QCD sum rules reexamined

The pionic coupling constants in the decays of the ${1}^{\ensuremath{-}+}$ hybrid meson are calculated. The double Borel transformation is invoked and the continuum contribution is subtracted. The decay widths of the processes ${1}^{\ensuremath{-}+}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\pi}{,f}_{1}\ensuremath{\pi},\ensuremath{\pi}\ensuremath{\gamma}$ are around 40, 100, 0.3 MeV, respectively. A comparison is made with previous calculations using three-point correlation functions.

New results on exotic mesons from BNL-E852

We have so far found evidence for two exotic mesons with the quantum numbers I G J PC = 1 −1 −+ at masses 1.4 and 1.6 GeV. They are seen in the decay channels πη, πϱ and πη′ with varying degrees of strengths.

Hadronic spectroscopy from the lattice: Glueballs and hybrid mesons

Lattice QCD determinations appropriate to hadron spectroscopy are reviewed with emphasis on the glueball and hybrid meson states in the quenched approximation. Hybrids are discussed for heavy and for light quarks. The effects of sea quarks (unquenching) are explored.

Exotic states and fundamental interactions at LEAR and DAΦNE

An overview is given of the main achievements obtained at the LEAR of CERN in the search for exotic mesons. The impact of these results on the present understanding of the hadronic interaction is outlined. Particular attention is devoted to the discovery of the ‖ 0(1500), the strong candidate for the ground state scalar glueball, and to the definite evidence of the ϱ(1400) , with exotic quantum numbers J PC = 1 −+, which is an excellent candidate for a hybrid meson. The remarkable hypernuclear physics program of DAΦNE, at the Frascati laboratory, and its prospects in exploring fundamental interactions is reviewed, with emphasis on the unique possibility offered to study weak non-mesonic decays of Λ-hypernuclei.

An analysis of early data on heavy exotic mesons based on the diquark cluster model

Early data with respect to heavy exotic mesons with narrow width (≤ 80MeV) found in π p reactions by Andersonet al. and Baudet al. in 1969–1970 are analyzed using the diquark cluster model. It is shown that the simple mass formula of the diquark cluster model, which involves no free parameters, can clearly reproduce the mass spectrum for the heavy exotic mesons indicated by the empirical data.

THE SPECTRUM OF THE HYBRID MESONS WITH HEAVY QUARKS FROM THE BS EQUATION

We solve the BS equation for the hybrid mesons with heavy quarks under instantaneous approximation. The kernel is chosen as the sum of a one-gluon-exchange potential and a linear confining potential. The equations are solved by the numerical method, and the spectrum of hybrid mesons [Formula: see text] and [Formula: see text] is obtained.

Masses and decay widths of heavy hybrid mesons

We first derive the mass sum rules for the heavy hybrid mesons to obtain the binding energy and decay constants in the leading order of heavy quark effective theory. The pionic couplings between the lightest 1(-+) hybrid (g) and the lowest three heavy meson doublers are calculated with the light cone QCD sum rules. With SUf(3) flavor symmetry we calculate the widths for all the possible two-body decay processes with a Goldstone boson in the final state. The total width of the 1(-+) hybrid is estimated to be around 300 MeV. We find that the dominant decay mode of the 1(-+) heavy hybrid is 1(-+) --> pi+1(+) where the 1(+) heavy meson belongs to the (1(+),2(+)) heavy meson doublet. Its branching ratio is about 80% so this mode can be used for the experimental search of the lowest heavy hybrid meson. [S0556-2821(99)01213-8].

Nonfactorizable contributions in hadronic weak decays of charm mesons

Two body decays of charm mesons are studied by describing their amplitude in terms of a sum of factorizable and non-factorizable ones. The former is estimated by using a naive factorization while the latter is calculated by using a hard pseudo-scalar-meson approximation. The hard pseudo-scalar-meson amplitude is given by a sum of the so-called equal-time commutator term and surface term which contains all possible pole contributions of various mesons, not only the ordinary $\{q\bar q\}$ but also four-quark $\{qq\bar q\bar q\}$, hybrid $\{q\bar qg\}$ and glue-balls. Naively factorized amplitudes for the spectator decays which lead to too big rates can interfere destructively with exotic meson pole amplitudes and the total amplitudes can reproduce their observed rates. The non-factorizable contributions can supply sufficiently large contributions to the color suppressed decays which are strongly suppressed in the naive factorization. A possible solution to the long standing puzzle that the ratio of decay rates for $D^0\to K^+K^-$ to $D^0\to \pi^+\pi^-$ is around 2.5 is given by different contributions of exotic meson poles.

Exotic meson spectroscopy from the clover action at β = 5.85 and 6.15

We repeat our original simulations of the hybrid meson spectrum using the clover action, as a check on lattice artifacts. Our results for the 1 −+ masses do not substantially change. We present preliminary results for the wave function of the 1 −+ state in Coulomb gauge.

Hybrid and orbitally excited mesons in full QCD

We present results for the hybrid meson spectrum produced by gluonic excitations in full QCD using Wilson fermions. For the spin-exotic mesons with J PC = 1 −+, 0 +−, and 2 +− we find the lightest state to be 1 −+ with a mass of 1.9(2) GeV. Results obtained for orbitally excited mesons are also presented.

Hybrid meson decay phenomenology

The phenomenology of a newly formulated model of hybrid meson decay is developed. The decay mechanism is based on the heavy quark expansion of QCD and the strong coupling flux tube picture of nonperturbative glue. A comprehensive list of partial decay widths of a wide variety of light, s{bar s}, c{bar c}, and b{bar b} hybrid mesons is presented. Results which appear approximately universal are highlighted along with those which distinguish different hybrid decay models. Finally, we examine several interesting hybrid candidates in detail. {copyright} {ital 1999} {ital The American Physical Society}

Heavy hybrids with constituent gluons

Hybrid meson energies are calculated in the static quark limit with the Dynamical Quark Model (DQM). In the DQM, transverse gluons are represented as effective constituents with a dynamically generated mass. Hybrid masses are determined within the Tamm-Dancoff approximation for the resulting relativistic Salpeter equation. Although the general features of the adiabatic potential surfaces correspond with lattice data, the results disagree on level orderings. Similar problems appear to exist in all constituent glue models of hybrids. We conclude that constituent gluons do not accurately represent soft gluonic degrees of freedom. The steps necessary to correct this deficiency are discussed.

Exotic mesons, locking states, and their role in the formation of the confinement barrier

We discuss a mechanism by which a set of $q\overline{q}$ states mixes with an exotic one, so that the exotic state accumulates the widths of the overlapping $\overline{q}q$ resonances. The broad state created this way acts as a ``locking'' state for the others. Using results of a previous analysis of the ${(IJ}^{\mathrm{PC}}{=00}^{++})$ wave, we estimate the mean radius squared of the broad state ${f}_{0}{(1530}_{\ensuremath{-}250}^{+90});$ it appears to be distinctly larger than the mean squared radii of the locked narrow states. This supports the idea about the constructive role of broad states in forming the confinement barrier.

Interpretation of experimentalJPCexotic signals

The authors investigate theoretical interpretations of the 1.4 GeV J{sup PC} exotic resonance reported by the E852 collaboration. It is argued that interpretation in terms of a hybrid meson is untenable. A K-matrix analysis shows that the 1.4 GeV enhancement in the E852 {eta}{pi} data can be understood as an interference of a non-resonant Deck-type background and a resonance at 1.6 GeV. A final state rescattering calculation shows that the 1.6 GeV hybrid has a {eta}{pi} width which is bounded above by 57 {+-} 14 MeV.

The masses of the $0^{++}$ and $0^{-+}$ light-quark hybrids using QCD sum rules

We calculate masses of the light-quark hybrid mesons with the quantum number $0^{++}$ and $0^{-+}$ by using the QCD sum rules. Two kinds of the interpolated currents with the same quantum number are employed. We find that the approximately equal mass is predicted for the $0^{-+}$ hybrid state from the different current and the different mass is obtained for the $0^{++}$ hybrid state from the different current. The prediction depends on the interaction between the gluon and quarks in the low-lying hybrid mesons. The mixing effect on the mass of the light-quark hybrid meson through Low-energy theorem has been examined too, and it is found that this mixing shifts the mass of hybrid meson and glueball a little.

Do hybrid mesons exist, do they mix with charmonium?

Abstract Hybrid c c g of quantum numbers 1−− are considered in a quark model with constituent quarks and gluon. The lowest JP=1− states may be built in two ways, lg=1 (gluon excited) corresponding to an angular momentum between the gluons and the c c system, while l c c =1 (quark excited) corresponds to an angular momentum between the c and the c. The lowest lying hybrid JP=1− state in the flux tube model is similar to the lg=1 in the quark-gluon model. In particular it verifies the selection rule that it cannot decay into two fundamental mesons. The l q q =1 hybrid may decay into two fundamental mesons, but with decay widths larger than 1 GeV, which tells that they do not really exist as resonant states. using a chromoharmonic potential, we find no mixing between the lg=1 and l c c =1 . More realistic potentials might induce a strong mixing between them, implying that no hybrid meson exist. If, on the contrary, such a strong mixing does not occur, we find, in agreement with the flux tube model, that only the lg=1 appears as a real resonant state. In such a case, hybrid mesons may exist as resonances only if they are decoupled from the ground state channel, which explains the difficulty to observe them experimentally. We reconsider accordingly the Ono–Close–Page scenario of mixing between charmonium and charmed-hybrid to explain the anomalies around 4.1 GeV. We find a very small mixing between radially excited charmonium and hybrid mesons, which forbids considering the ψ(4.040) and ψ(4.160) as combinations of 3S charmonium and lg=1 hybrid meson with a large mixing.

Photoproduction and electroproduction ofJPC=1−+exotics

We estimate the kinematic dependence of the exclusive photo-- and electroproduction of $J^{PC}=1^{-+}$ exotic mesons due to $\pi$ exchange. We show that the kinematic dependence is largely independent of the exotic meson form factor, which is explicitly derived for a $1^{-+}$ isovector hybrid meson in the flux-tube model of Isgur and Paton. The relevance to experiments currently planned at Jefferson Lab is indicated.

Quantum number exotic hybrid mesons and large Nc QCD

Exotic mesons with quantum numbers of a hybrid (qqg) such as JPC=1−+are shown to exist as narrow resonant states in the large Nc limit of QCD. The width of these states is proportional to 1/Nc. Possible phenomenological implications for the world of Nc=3 are discussed.

Coarse lattice results for glueballs and hybrids

A review of new results from lattice simulations of glueballs and heavy-quark hybrid mesons is presented.

Exotic hybrid mesons and four-quark states

We calculate masses of mesons with exotic quantum numbers in the quenched approximation. Using a four quark source operator, we demonstrate mixing of the 1 −+ meson with four-quark states. Using the conventional Wilson quark action, we calculate both at reasonably light quark masses, intending to extrapolate to small quark mass, and near the charmed quark mass, where we calculate the masses of some ccg hybrid mesons. The hybrid masses are large — over 4 GeV for charmonium and more than twice the vector meson mass at the strange quark mass.