would constitute background to its measurements. It is designed to reach a sensitivity (in a small part of the mass-range probed) where neutrinos become a significant background. As of 2019, the upgrade was on-going and first light was expected in 2020. The XENONnT detector was under construction in March 2020. Even with the problems posed by COVID-19, the project was able to finish construction and move forwards into commissioning phase by mid 2020. Full detector operations commenced in late 2020. In September 2021, XENONnT was taking science data for its first science run, which was ongoing at the time. References Further reading External links The XENON Experiment XENON home page at the University of Chicago XENON home page at Columbia University XENON home page at the University of Zurich XENON home page at Rice University XENON home page at Brown University Katsuhi Arisaka, XENON at University of California, Los Angeles Dark matter limit plotter with the latest results from XENON and other experiments Enlightening the dark, CERN Courier, Sep 27, 2013 Experiments for dark matter search