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Quantum chromodynamics (QCD) is the modern theory of strong interactions. Quarks and antiquarks interact extit{via} gluons, the gauge bosons, and form well-know bound states, namely mesons and baryons. This non-Abelian gauge theory predicts the existence of unconventional states of quarks and gluons: Exotic hadrons. Their observation remains a difficult task since their properties are poorly known. Their theoretical study is a challenging task and will guide experimentalists in their work. This thesis is devoted to two main types of exotic hadrons: Hybrid mesons and glueballs. Hybrid mesons are mesons in which the gluon field is in an excited state. In constituent models, the excitation of the flux tube is interpreted in term of a constituent gluon. In this thesis, the connection between the two pictures, flux tube excitation and constituent gluon, is demonstrated. Using the technique of the auxiliary field, we reproduce, from the three-body system quark-antiquark-gluon, the excitations of the quark-antiquark potential observed in lattice QCD. We complete our study of mesons with exotic quantum numbers by performing a analysis of the low-lying spectrum. Glueballs are hadronic states with no valence quarks. Theoretical developments suggests that confined gluons gain a constituent mass inside glueballs. According to this, a gluon can be considered as a heavy spin-1 particle. Two- and three-gluon glueballs are then similar of heavy meson and baryon systems. We preformed a complete study of the low-lying spectrum of these glueballs. The comparison with the pure gauge results from lattice QCD showed a disagreement and led us to the conclusion that the gluon degree-of-freedom was not correctly taken into account. Indeed, the implementation of transverse gluons at the level of the wave functions solved this problem for two-gluon glueballs. For both systems, hybrid mesons and glueballs, we used semi-relativistic Hamiltonians since they remain valid for massless particles. A code in Gaussian basis was developed to solve our eigenvalue problems. For this purpose, we found the matrix elements between Gaussian functions for various operators.

<p>This thesis treats the mass range of charmonium states and excited gluonic fields in two experiments, BESII and PANDA, and outlines a phenomenological model that connects them.</p><p>In BESII, <i>e</i>⁺<i>e</i>^– form a charmonium initial state, which is utilised as a source for secondary particles. The analysed channels, <i>ψ</i>´→ <i>γK</i>⁺<i>K</i>^– and <i>ψ</i>´→ <i>γπ</i>⁺<i>π</i>^–, give access to intermediate scalar states such as the two glueball candidates: f₀(1500) and f₀(1710). The f₀(1710) is indeed observed in decay into both <i>π</i>⁺<i>π</i>^– and <i>K</i>⁺<i>K</i>^– and the f₀(1500) is accepted as a necessary part of the <i>π</i>⁺<i>π</i>^– signal at the moderate 5% level. In addition, we observe the two tensor states f₂(1270) (in both channels) and f₂´(1525) (in <i>K</i>⁺<i>K</i>^–), but the need for the f₂´(1525) is not firmly established. The region around 2 GeV/<i>c</i>² is fitted with an f₄(2050) and an f₀(2200) in <i>π</i>⁺<i>π</i>^–. This region is fairly flat in <i>K</i>⁺<i>K</i>^– with a slight peak at the f₀(2200). Branching ratios for all eight channels are given. A fit to the angular distribution of ψ´→ γ f₂(1270) → <i>γ π</i>⁺<i>π</i>^–gave two possible solutions for the relative importance of helicity projections zero, one and two.</p><p>The future <i>pp</i>bar experiment PANDA is still in the development phase; important physics goals have been defined and we are now taking on the laborious task of constructing a detector that is able to fulfil them. A simulation investigation of a theoretically preferred <i>J</i><i>PC</i>=1^–+ charmonium hybrid (<i>H</i><i>c</i>) is presented: <i>ppbar</i> → <i>H</i><i>c</i><i>π</i>⁰/<i>η</i>, <i>H</i><i>c</i> → <i>χ</i><i>c</i>₁ (<i>π</i>⁰<i>π</i>⁰)<i>S–wave</i>, <i>χ</i><i>c</i>₁ → <i>J</i>/<i>ψπ</i>⁰, with a final state of seven photons and a lepton pair. To detect this channel next to full coverage of CM phase space is needed and as little material as possible before the electromagnetic calorimeter. </p><p>A second simulation study of <i>pp</i>bar → <i>η</i><i>c</i> → <i>γγ</i> at PANDA, suggests that the channel should be possible to detect with a signal-to-background ratio of 5±1 and a detection efficiency of at least 10%. </p><p>By assuming a constant matrix element we obtain a relation between the decay width for <i>ψ</i> → <i>pp</i>bar+<i>m</i>, which has been measured at BES for several cases, and the cross section for <i>pp</i>bar charmonium production in association with the same light meson, <i>m</i> (at for example PANDA). Cross sections of ~300–3000 pb were predicted for J/ψ production and ~30 pb for <i>ψ</i>' production. Isoscalars seem to be preferred to isovectors in <i>J</i>/<i>ψ</i> production, this might however be an artefact of simplifications within the model. A comparison with the only measured cross section, <i>pp</i>bar → <i>J</i>/<i>ψπ</i>⁰, suggests that the model is useful as a first estimate.</p>

This thesis treats the mass range of charmonium states and excited gluonic fields in two experiments, BESII and PANDA, and outlines a phenomenological model that connects them. In BESII, e+e– form a charmonium initial state, which is utilised as a source for secondary particles. The analysed channels, ψ´→ γK+K– and ψ´→ γπ+π–, give access to intermediate scalar states such as the two glueball candidates: f0(1500) and f0(1710). The f0(1710) is indeed observed in decay into both π+π– and K+K– and the f0(1500) is accepted as a necessary part of the π+π– signal at the moderate 5% level. In addition, we observe the two tensor states f2(1270) (in both channels) and f2´(1525) (in K+K–), but the need for the f2´(1525) is not firmly established. The region around 2 GeV/c2 is fitted with an f4(2050) and an f0(2200) in π+π–. This region is fairly flat in K+K– with a slight peak at the f0(2200). Branching ratios for all eight channels are given. A fit to the angular distribution of ψ´→ γ f2(1270) → γ π+π–gave two possible solutions for the relative importance of helicity projections zero, one and two. The future ppbar experiment PANDA is still in the development phase; important physics goals have been defined and we are now taking on the laborious task of constructing a detector that is able to fulfil them. A simulation investigation of a theoretically preferred JPC=1–+ charmonium hybrid (Hc) is presented: ppbar → Hcπ0/η, Hc → χc1 (π0π0)S–wave, χc1 → J/ψπ0, with a final state of seven photons and a lepton pair. To detect this channel next to full coverage of CM phase space is needed and as little material as possible before the electromagnetic calorimeter. A second simulation study of ppbar → ηc → γγ at PANDA, suggests that the channel should be possible to detect with a signal-to-background ratio of 5±1 and a detection efficiency of at least 10%. By assuming a constant matrix element we obtain a relation between the decay width for ψ → ppbar+m, which has been measured at BES for several cases, and the cross section for ppbar charmonium production in association with the same light meson, m (at for example PANDA). Cross sections of ~300–3000 pb were predicted for J/ψ production and ~30 pb for ψ' production. Isoscalars seem to be preferred to isovectors in J/ψ production, this might however be an artefact of simplifications within the model. A comparison with the only measured cross section, ppbar → J/ψπ0, suggests that the model is useful as a first estimate.