Skip to main content

Cryogenic wide-Area Light Detectors 
with Excellent Resolution

Final Report Summary - CALDER (Cryogenic wide-Area Light Detectors with Excellent Resolution)

CALDER introduced a new detector technology for particle physics experiments, motivated by the
long-standing and not yet solved problem between matter and antimatter. Their balance was broken just after the Big Bang, and now there is only matter that surrounds us. Why did matter prevail? What happened to the antimatter? The answer may come from the observation and discovery of the Majorana neutrino, a particle that is very difficult to detect.

The detectors invented within CALDER are operated at temperatures close to absolute zero, between 10 and 200 mK. They are composed of silicon or sapphire substrates, acting as radiation absorbers and coupled to superconducting sensors called kinetic inductance detectors (KIDs). The substrates are 400 um thick and feature an absorbing area between 4 and 25 cm^2. The KIDs are made by 60 nm films of aluminum or aluminum-titanium and are deposited on the substrates. When radiation impinges on the substrate, it suddenly generates atomic vibrations, called phonons, which propagate in the substrate until they reach the KID and generate an electrical signal.

Aside the sensing area of several cm^2, the detectors feature good energy resolution (around 10 optical photons), fast response (10-20 us), scalability to hundreds of sensors and high resistance to vibrations. Before CALDER a cryogenic detector with all this features at once did not exist, making it a very promising technology not only for searches of Majorana neutrinos, but also for other rare and low-energy processes. One example is the detection of Dark Matter, an unknown form of matter that permeates our Universe and not yet discovered.