First results of the calorimetric spectrometer for the beta decay of rhenium-187

An outlook on the relevant progresses in the rhenium experiment with cryogenic detectors that has been made in the past year will be presented. We will discuss how the surrounding environment causes a ripple-like perturbation on the energy spectrum called Beta Environmental Fine Structure (BEFS). In 3 months of effective data acquisition we collected about 6 millions of events, achieving the sensitivity to observe for the first time the BEFS effect in the energy range 300-1600 eV, where its amplitude is at level of 1%. This distortion will have to be taken into account in the experiment in order to identify the kink in the high-energy end of the decay spectrum caused by a light neutrino.