Spectroscopy ofQ\bar Qg hybrid mesons

Hybrid mesons composed of a quark, an antiquark, and a gluon are studied in the case of heavy quarks. Their masses are calculated with the potential model which can interpret heavy quarkonium spectroscopy. The ground state of the hybrid mesons \(c\bar cg\) and \(b\bar bg\) is found to be almost spherically symmetric, whereas that of \(t\bar tg\) is two-centered as anH ₂ ⁺ molecule. The \(b\bar bg\left[ {t\bar tg} \right]\) ground state turns out to have a mass below the \(B\bar B\left[ {T\bar T} \right]\) threshold. The excited states contain 0^??, 1^?+ exotic states and 1^?? states which may be examined bye ⁺ e ^? colliders.     

New limits on Primakoff production of hybrid mesons

I discuss constraints on properties of isoscalarJ ^PC =1^?+ exotic hybrid mesons, assuming their dominant decay mode is ηπ. This work expands on a similar study by the Rochester-Minnesota-Fermilab collaboration, which excluded ?π as the dominant decay channel for such hybrids. The experimental limits are based on Primakoff production of such states and on a VDM argument relating their radiative widths to their ?π decay modes. Using data on coherent production of ηπ⁺ systems in π⁺ collisions with nuclei, I obtain few percent limits on the ?π branching ratios for hybrid masses ?1.5 GeV.     

ρ meson decays of heavy hybrid mesons

We calculate the ρ meson couplings between the heavy hybrid doublets H~h/S~h/M~h/T~h and the ordinary qQˉ doublets in the framework of the light-cone QCD sum rule. The sum rules obtained rely mildly on the Borel parameters in their working regions. The resulting coupling constants are rather small in most cases.     

Adiabatic potentials and spectra of heavy hybrid mesons

Using the QCD string approach, adiabatic potentials and spectra of bb hybrid mesons are calculated. The results are compared with lattice studies.     

Excited flux tube from q¯g hybrid mesons

In the framework of quark models, hybrid mesons are either seen as two-body qˉ systems with an excited flux tube connecting the quark to the antiquark or as three-body qˉg systems including a constituent gluon. In this work we show that, starting from the three-body wave function of the qˉg hybrid meson in which the gluonic degrees of freedom are averaged, the excited flux tube picture emerges as an equivalent qˉ potential. This equivalence between the excited flux tube and the constituent-gluon approach is confirmed for heavy hybrid mesons but, for the first time, it is shown to hold in the light sector too, provided the contribution of the quark dynamics is correctly taken into account.     

Neutral B-meson decay and the search for hybrid mesons

We discuss the possibility that the decay of the neutral B mesons via a non-spectator mechanism might have a significant branching fraction into $\text{(}\text{q}\text{q}\text{g}\text{)}$ states. The lightest such hybrid mesons would be recognizable as narroe state of mass 1.6 ± 0.4$\text{GeV}\text{c}{}^2$ decaying predominantly into hadrons containing strange quarks.     

Electroweak production of hybrid mesons in a flux-tube simulation of lattice QCD

We make the first calculation of the electroweak couplings of hybrid mesons to conventional mesons appropriate to photoproduction and to the decays of B or D mesons. E1 amplitudes are found to be large and may contribute in charge exchange gammap-->nH(+) allowing production of (among others) the charged 1(-+) exotic hybrid off a(2) exchange. Axial hybrid meson photoproduction is predicted to be large courtesy of pi exchange, and its strange hybrid counterpart is predicted in B-->psiK(H)(1(+)) with branching ratio B approximately 10(-4). Higher multipoles and some implications for hybrid charmonium are briefly discussed.     

Heavy quark potentials and hybrid mesons from SU(3) lattice gauge theory

The potentials between heavy quarks are evaluated in SU(3) lattice guage theory using a combined variational and multihit technique. We present results for the ground state potential together with the first gluonic excited mode which is relevant to hybrid mesons.     

Top mesons

The possibility of formation for a bound state of a quark and a lighter one is investigated using potential model predictions and heavy quark effective theory approach. Resulting estimates for the 1S–2S splitting of the energy levels are compared to the total top decay width . As for the case of toponium, our conclusions show that the probability of formation for T–mesons is negligibly small due to the high top mass value. Received: 2 April 1997