Exotic states of matter : Molecular effects in investigations of weak, strong, and long-range forces

Abstract: Some cases in which the interpretation of experiments in nuclear, particle, and low temperature physics requires understanding of molecular effects have been studied.Neutrino-mass determination from β decay of T2 requires knowledge of the energy loss due to molecular excitations of the daughter HeT+ molecule. The theoretical final-state distribution has been studied, in particular the role of nonadiabatic effects. Possible origins of unphysical experimental results leading to a "negative mass squared" are discussed, as are various methods for experimental verification of the final-state distribution.Pionic hydrogen (pπ-) is used in experiments that determine the mass difference mπ- - mp0, and other fundamental properties of pions. Formation of three-body resonances (ppπ-)' in the cascade of pionic hydrogen atoms has been studied. The decay of these state provides an efficient accelerationmechanism for the pionic atoms, with impact on the experimental analysis.Cold antihydrogen will be used at CERN to study the CPT theorem and the weak equivalence principle. We study the collisional interaction of antihydrogen with ultracold hydrogen. It has been found that cooling dominates over annihilation at antihydrogen temperatures down to ~ 0.1 K.In Bose-Einstein condensation of atomic hydrogen the shape of the 1s-2s line is used to probe the temperature and density. Long-range interactions between excited 2s atoms have been studied in order to improve the understanding of line shapes above and below the condensation temperature.