Studies on Parity Non-conservation in Atomic Microwave Transitions

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It is clear that laser experiments on atoms can provide important information on one of the most crucial questions of elementary particle physics, i.e., the validity of combining weak interactions and electro-magnetic interactions. The Weinberg-Salam theory (Standard Model) predicts the existence of additional weak interactions between the particles, electrons, protons and neutrons which from an atom. The weak interaction violates parity while the Electro-magnetic interaction conserves it. Therefore, it is possible to set up an experiment to search a very tiny explicitly parity violating effect in the presence of a very much larger than parity conserving backgrounds. The effect of weak neutral currents between electrons and the atomic nucleus could be detected in atoms with large atomic numbers, Z,since the effect was found to be roughly proportional to Z^3.We measured parity nonconserving (PNC) optical rotation on the optical transition in atomic thalium and lead. The result is consistent with current calculations based on the standard model. Moreover, limits have been set on the much smaller nuclear spin-bependent rotation amplitude. This is also consistent with theoretical estimates which include a nuclear anapole moment contribution.We are now investigating parity nonconservation effect on the microwave transition in hyperfine structures of Rb atom. Furthermore, the experimental results, when combined with the relevant atomic calculations, lead to a value for the mass of the Zo boson or, alternatively, place a limit on physics beyond the standard model through the isospin-conserving parameter, S.