Glueball wave functions and production cross sections.

摘要

Three topics are studied in this dissertation.; Using QCD sum rules, I first calculate the first few moments of the distribution amplitude of the pseudoscalar glueball, a bound state of gluons. The distribution amplitude is the momentum wave function integrated over the transverse momentum. QCD sum rules are a method of finding hadronic parameters using perturbative QCD. I use an approximation in which the glueball is treated as a narrow resonance. The moments of the distribution amplitude then give the corresponding first few coefficients of the distribution amplitude for the glueball expanded in Gegenbauer polynomials. The distribution amplitude is rather close to its asymptotic form, and the glueball's "decayconstant" is about 105 MeV for a pseudoscalar glueball mass of 2.0 GeV.; Using the previously calculated distribution amplitude, I calculate the normalized differential cross section for two-photon pseudoscalar glueball plus meson production, {dollar}gamma + gammato G + pisp0{dollar}. I compare to a previous calculation and to {dollar}gamma + gammatopisp0 + pisp0{dollar}.; Lastly, I show that very high momentum transfer semi-inclusive photoproduction of pions from nucleons, {dollar}gamma ptopi X{dollar}, is dominated by a subprocess where the pions are produced directly. Although the "direct subprocess" may be thought of as a limiting case of a quark fragmentation subprocess, it is an exclusive process at the quark level, fully calculable using perturbative QCD, and thus distinct from the usual thinking about fragmentation processes. The numerical results, concentrating on neutral pions, indicate that the direct subprocess is dominant at pion transverse momenta slightly higher than those already measured. Incidentally, the integral over the pion distribution amplitude in the present case is the same as that for the pion electromagnetic form factor, but the momentum transfers involved correspond to measuring the pion form factor at momentum transfers up to several hundred GeV{dollar}sp2{dollar}. These calculations can now be extended to glueball production at high transverse momentum.