Isospin Breaking in Neutron β-decay and SU(3) Violation in Semi-leptonic Hyperon Decays

الأصل · EN

Present precision measurements of the neutron life time lead to a CKM matrix element |Vud| which is three standard deviations off the value inferred from heavy quark decays etc. We investigate the possibility whether isospin-breaking effects in the neutron-to-proton vector current transition matrix element < p|V+₀|n >=1+δgᵥ could eventually close this gap. For that we calculate in chiral perturbation theory the effect of pion and kaon loops on the matrix element < p|V+₀|n > taking into account the mass differences of the charged and neutral mesons. We find a negligibly small isospin-breaking effect of δgᵥ ≃ -4 · 10⁻⁵. The crucial quantity in the analysis of neutron beta-decay precision measurements is thus the radiative correction term Δᵣ. Furthermore, we calculate in heavy baryon chiral perturbation theory the SU(3) breaking effects on the vector transition charges of weak semi-leptonic hyperon decays. We find for these quantities channel-dependent relative deviations from the SU(3) limit which range from -10% to +1%.