Speaker
Description
XENONnT was successfully commissioned in 2021 and has started science data taking. In addition to the new TPC, the experiment was augmented by a new water Cherenkov neutron-veto surrounding the central detector. In this talk, we present the first results of XENONnT’s nuclear recoil (NR) response calibration as well as the calibration of the neutron-veto detection efficiency. This NR calibration, to our knowledge for the first time in a large liquid xenon TPC, employs tight coincidence tagging of nuclear recoils, utilizing the 4.4 MeV gamma-ray from an Americium-Beryllium source in coincidence with the emitted neutron. We show that this results in an effectively background-free NR calibration at a reduced S1 threshold by removing accidental coincidences and other backgrounds. The reverse event topology – 4.4 MeV gamma in the TPC and neutron in the veto detector – is used to measure the neutron veto detection efficiency.