Probing Anomalous Contributions to Triple Boson Couplings
Abstract
The Standard Model of the unified electroweak interactions (SM) has been confirmed by all experiments to date. This empirical evidence for the validity of the theory has been almost entirely restricted to the interactions between the matter particles, the fermions, and the force mediating gauge particles, the bosons. However, a fundamental prediction of the SM is that the gauge bosons should also interact amongst themselves; both trilinear and quartic couplings are predicted. These boson selfinteractions are a consequence of the nonabelian nature of the electroweak gauge group and are essential for both the unitarity and renormalizability of the theory. Future colliders like LEP2 e^+e^ at sqrt {s} = 190 GeV and the NLC, e^+e ^ at sqrt{s} = GeV, will make possible direct tests of the gauge self couplings by the measurement of processes which get tree level contributions from these vertices. This thesis describes the investigation of the triple gauge boson couplings WW_gamma and WWZ through the four lepton production processes e^+e^to l^+nu l^{'}nu where we consider all possible final state lepton configurations. The analysis is performed at the energies of sqrt {s} = 500 GeV and sqrt{s } = 1 TeV. By examining the sensitivity of the total crosssections and experimental distributions of the above processes to variations in the triple boson vertex parameters, in particular the anomalous magnetic moment parameter kappa_{V} and the CP violating ~{ kappa}_{V} and ~{lambda}_{V} , we determine the detection potential of these processes for such deviations. Assuming an integrated luminosity of 50 fb ^{1} for these future colliders, we find that the anomalous magnetic moment parameter kappa_{V} could be measured to within the order of a few percent, +/ (23)% of its Standard Model value; the higher energy of 1 TeV can improve the constraints by a factor of 2 for certain of the processes. Limits of this level are a significant improvement on the bounds of ~{+/ }10% predicted for LEP2 and probe both the loop corrections to the vertices as well as the corrections predicted by certain extensions to the Standard Model. Independent constraints on kappa_{gamma } and kappa_{Z} might be determined by the implementation of suitable phase space cuts; these independent limits are of the order of +/20% for kappa _{Z} and +/10% for kappa_{gamma} . A polarized beam facility would access the rich helicity structure of the processes; with such information we could improve both the limits on kappa _{V} as well as the ability to discriminate between kappa_{ gamma} and kappa_ {Z}. The CP violating couplings ~ {kappa}_{V} and ~{lambda}_{V } could be measured to within limits of the order of +/0.15 and +/ 0.005 respectively. The "purest" signature of such CP violation would be +/0.005 respectively. The "purest" signature of such CP violation would be asymmetries in event rates between CP conjugate states; we find that, for ~{kappa}_ {V}, ~{lambda}_ {V} = 1, the expected magnitude for such asymmetries in the total cross section is below the statistical significance level of 12%. The asymmetries in the individual helicity amplitude contributions to the total cross section can however exceed this significance level; polarized e^+e^ beams would be necessary to explore this effect.
 Publication:

Ph.D. Thesis
 Pub Date:
 January 1995
 Bibcode:
 1995PhDT.......106M
 Keywords:

 CP VIOLATION;
 GAUGE SELF COUPLING;
 Physics: Elementary Particles and High Energy