20 years of cryogenic particle detectors: past, present and future

In 1984 different authors presented a new approach for detecting elementary particles: the cryogenic (sometimes also called bolometric) particle detector. The basic idea was very simple but at the same time completely different with respect to other classical methods. The generation of the signal is produced by phonons with a mean energy around 10−4−10−5 eV and this aspect changes completely the evaluation of the theoretical energy resolution. In these 20 years substantial progress has been made in the development of cryogenic particle detectors, many experiments have been realized and some are still running. Detector performances are greatly improved and very massive detectors have been constructed. For specific experiments, detectors with simultaneous measurements of heat and ionization (or scintillation) were also developed. Cryogenic particle detectors have been applied in many fields, not only in particle physics experiments, thanks to some peculiar characteristics that they exhibit. Experiments on double beta decay take advantage from the good energy resolution and the flexibility in selecting materials; low energy thresholds and high efficiencies to nuclear recoils of these detectors are very interesting in the search for dark matter; the impressively high energy resolution of microcalorimeters is suitable for X-ray spectroscopy and direct neutrino mass measurements. Other experiments in particle physics use the cryogenic approach, but it is important to note that applications to surface analysis with Total Reflection X-ray Fluorescence (TXRF) for industry and measurements of protein fragments for biology have been also proposed. In the near future, new experiments will be realized using this technique. Very important technical challenges are still open, such as: realization of very large detectors (at the one ton scale), improvements in energy resolution and energy thresholds, maximization of the time resolution. A short history and the state of the art of cryogenic particle detectors will be presented; some aspects of their applications in the past and for the future will be briefly discussed.