Precision spectroscopy of Bi-210 as a basis for the detection of CNO-neutrinos

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A fundamental process of stellar energy production is the so called CNO-cycle. Even proposed in the 1930ies the associated CNO-neutrinos haven't been detected.In the last decade experiments based on liquid scintillators have been dominated solar neutrino research, especially the Borexino experiment which has studied various neutrino reates from the pp-cycle.For a first detection of CNO-neutrinos extreme low backgrounds is essential. One of the major backgrounds sources is the forbidden beta decay of Bi-210. It's spectral shape similarity of the electrons and correlations to the recoil spectrum of CNO is very hard to disentangle. As it is a forbidden decay the theoretical modelling is non-trivial. Hence, the aim of this grant application is to measure the spectral shape of the Bi-210 electrons with high precision. Based on work already performed, in a first step the beta allowed beta decay spectrum of Si-31 should be measured and the developed analysis tools will be checked and validated. In a second step is the precision measurement of the Bi-210 beta spectrum. The outcome of this measurement will be used to make sensitivity estimates for liquid scintillator detectors. In a final step the CNO-analysis including the measured spectroscopic spectrum of Bi-210 will be performed within the Borexino experiment.