Calculations in perturbative QCD and analyses involving scalar mesons

Abstract

The thesis is split into two independent parts. In part I we discuss the phenomenology of jets in e(^+)e(^-) annihilation at small relative transverse momentum, with a view to testing higher order perturbative QCD (viz. the quark form factor). We phenomenologically extrapolate the quark form factor to cover the whole range in transverse momentum by using the exact 0(αs) cross section in the Parisi-Petronzio prescription (PPP). This then enables us to calculate the transverse momentum distribution of charged hadrons at small transverse momentum; we show that this is a poor way of testing the quark form factor, due to problems in fragmentation. Energy-energy correlations at small angles are found to be a much easier cross section to deal with. However, although the quark form factor is compatible with the data in energy-energy correlations, intrinsic transverse momentum dependence was incorporated in a very naive way, using the smearing function ρ(b) borrowed from Drell-Yan (where it describes hadronic structure). Fragmentation and intrinsic transverse momentum can be incorporated in a more physically meaningful way using the appropriate evolution equations. Erroneous approximations stemming from incorrect kinematic limits and misleading leading logarithms are discussed and corrected. This then allows a calculation of the energy weighted acollinearity of jets using a numerical solution of the evolution equations. Results are obtained in both singlet and non-singlet sectors and shown to be compatible with data at Q=30 Gev. The non-singlet sector is shown to be the dominant one at both Q=30 and at 100 Gev, where predictions are also made for the acollinearity. The effect of intrinsic transverse momentum is found to be much more significant in the evolution equation approach than when using the PPP, although at Q=100 Gev this effect is much lessened. Calculations using two-loop Altarelli-Parisi probabilities are discussed and it is demonstrated that these cannot be relied upon to give an unambiguous description of the data, due to gauge and renormalization scheme dependence. Various forms of the running couplingαs are used, but the data as yet does not show a strong preference for one or another. In part II we are concerned with analyses involving the S* and related scalar mesons. We investigate resonant effects in the isoscalar S wave scattering near the KK̅ threshold using data on ππ and KK̅ production. Various coupled channel parameterizations are considered, and using information from below and above KK̅ threshold, the parameters of the S* and ɛ, resonance effects are determined. The ɛ (1400) is found to be in agreement with an ANL analysis and the S* is compatible with a KK̅ bound state picture. We also study interference effects between the (P wave) φ meson and the underlying (K(^-)K(^+)) S wave in the reaction K(^-)p→(K(^-)K(^+)) ٨ at 4.2 Gev/c. A model independent amplitude analysis of the double multipole moments is performed and we investigate the implications for the KK̅→KK̅ S wave amplitude.