The purpose of this work is to evaluate the ratio of the vector and axial vector coupling constants in the beta-decay of Rb^87. Particular attention is given to determining the sign of the ratio. All this is accomplished mainly by a conic analysis of the beta-spectrum and the calculation of a matrix element ratio. The results obtained indicate that the ratio of the coupling constants is negative. Due to uncertainties in nuclear matrix elements, only an approximate absolute value for the ratio can be secured. These results are consistent with other present evidence. / Thesis / Master of Science (MSc)

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This work is included in a broader research of the hadron theory group of Uppsala University and its collaborators tackling the quest for an understanding of the quark distribution inside hadrons by joining threedifferent approaches of QCD namely chiral perturbation theory, dispersion theory and lattice QCD. This thesis contributes by computing in chiral perturbation theory, the quark-masses dependence of form factors. The next-to-next-to-Leading order (NNLO) contribution to the form factors is calculated from one-loop diagrams which brings hadron-masses dependences. The hadron masses are themselves dependent on quark masses. Consequently, the quark-mass dependence of the hadron masses is also addressed in this thesis.The studied process Ω− → W−Ξ0 possesses too many one-loop diagrams to be treated entirely here. This work focuses on the axial-vector sector and more specifically the part coming from the diagrams linear in the low-energy constant hA (see figure 2).To do so, Mathematica and specifically the packages FeynCalc, FeynHelpers and Package X are used. Vector transition form factors at NNLO are presented in the thesis of my colleague Magnus Bertilsson.The present thesis demonstrates that the calculational framework is feasible and paves the way for a complete NNLO calculation.