XENON

The XENON dark matter research project, operated at the Italian Gran Sasso National Laboratory, is a deep underground detector facility featuring increasingly ambitious experiments aiming to detect hypothetical dark matter particles.

The experiment detects scintillation and ionization signals produced when external particles interact in the liquid xenon volume, to search for an excess of nuclear recoil events against known backgrounds.

The applied electric field prevents recombination of all the electrons produced from a charged particle interaction in the TPC.

This fiducial volume has a greatly reduced rate of background events as compared to regions of the detector at the edge of the TPC, due to the self-shielding properties of liquid xenon.

For a given amount of energy deposited by a particle interaction in the detector, the ratio of S2/S1 can be used as a discrimination parameter to distinguish electronic and nuclear recoil events.

XENON10 was intended as a prototype detector, to prove the efficacy of the XENON design, as well as verify the achievable threshold, background rejection power and sensitivity.

This result excluded some of the available parameter space in minimal Supersymmetric models, by placing limits on spin independent WIMP-nucleon cross sections down to below 10×10−43 cm2 for a 30 GeV/c2 WIMP mass.

[5] Due to nearly half of natural xenon having odd spin states (129Xe has an abundance of 26% and spin-1/2; 131Xe has an abundance of 21% and spin-3/2), the XENON detectors can also be used to provide limits on spin dependent WIMP-nucleon cross sections for coupling of the dark matter candidate particle to both neutrons and protons.

As WIMP interactions are expected to be extremely rare events, a thorough campaign was launched during the construction and commissioning phase of XENON100 to screen all parts of the detector for radioactivity.

In doing so the design goal of <10−2 events/kg/day/keV [7] was reached, realising the world's lowest background rate dark matter detector.

In each science run, no dark matter signal was observed above the expected background, leading to the most stringent limit on the spin independent WIMP-nucleon cross section in 2012, with a minimum at 2.0×10−45 cm2 for a 65 GeV/c2 WIMP mass.

The detector project team, called the XENON Collaboration, is composed of 135 investigators across 22 institutions from Europe, the Middle East, and the United States.

While no WIMPs or dark matter candidate signals were officially detected, the team did announce a record low reduction in the background radioactivity levels being picked up by XENON1T.

[17] In April 2019, based on measurements performed with the XENON1T detector, the XENON Collaboration reported in Nature the first direct observation of two-neutrino double electron capture in xenon-124 nuclei.

This measurement represents a first step in the search for the neutrinoless double electron capture process, the detection of which would provide insight into the nature of the neutrino and allow to determine its absolute mass.

[23] Three explanations were considered: existence of to-date-hypothetical solar axions, a surprisingly large magnetic moment for neutrinos, and tritium contamination in the detector.

Apart from a larger xenon target in its time projection chamber the upgraded experiment will feature new components to further reduce or tag radiation that otherwise would constitute background to its measurements.

Even with the problems posed by COVID-19, the project was able to finish construction and move forwards into commissioning phase by mid 2020.

at 28 GeV with 90% confidence level,[33] jointly on the same date the LZ experiment published its first results too excluding cross sections above