  We study theoretically the interaction-induced generation of mesoscopic
coherent spin state superpositions (small cat states) from an initial coherent
spin state in bimodal Bose-Einstein condensates and the subsequent phase
revival, including decoherence due to particle losses and fluctuations of the
total particle number. In a full multimode description, we propose a
preparation procedure of the initial coherent spin state and we study the
effect of preexisting thermal fluctuations on the phase revival, and on the
spin and orbito-spinorial cat fidelities.
