Neutrino mass measurements using cryogenic detectors

The determination of the absolute mass scale of neutrinos is one of the most important challenges in Particle Physics. The shape of the endpoint region of $β$-decay and electron capture (EC) spectra depends on the phase space factor, which, in turn, is function of the neutrino mass eigenstates. High energy resolution and high statistics measurements of $β$- and EC spectra are therefore considered a model-independent way for the determination of the neutrino mass scale. Since almost four decades, low temperature microcalorimeters are used for the measurement of low energy $β$- and EC spectra. The first efforts were focused on the development of large arrays for the measurement of the $^{187}$Re $β$-spectrum. In the last ten years, the attention moved to EC of $^{163}$Ho. This choice was mainly motivated by the very good performance which could be achieved with low temperature microcalorimeters enclosing $^{163}$Ho with respect to microcalorimeters with absorber containing $^{187}$Re. The development of low temperature microcalorimeters for the measurement of the finite neutrino mass is discussed and, in particular, the reasons for moving from $^{187}$Re to $^{163}$Ho. The possibility to reach sub-eV sensitivity on the effective electron neutrino mass with $^{163}$Ho, thanks to the multiplexing of large microcalorimeter arrays is demonstrated. In conclusion, an overview on other nuclides which have been proposed as good candidates, motivated by the excellent performance of low temperature microcalorimeters is presented.

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