The KAGRA underground environment and lessons for the Einstein Telescope

Understand

The KAGRA gravitational-wave detector in Japan is the only operating detector hosted in an underground infrastructure.

• Underground sites promise a greatly reduced contribution of the environment to detector noise thereby opening the possibility to extend the observation band to frequencies well below 10 Hz.
• For this reason, the proposed next-generation infrastructure Einstein Telescope in Europe would be realized underground aiming for an observation band that extends from 3 Hz to several kHz.
• However, it is known that ambient noise in the low-frequency band 10 Hz - 20 Hz at current surface sites of the Virgo and LIGO detectors is predominantly produced by the detector infrastructure.