Barely new from the dark side

I wrote a blog about dark matter that accounts the most of mass of the universe. XENONnT is the latest dark matter detector generation located at the Gran Sasso International Laboratory in Italy. It contains 5.9 tons of liquid xenon waiting for dark matter particles crashing into xenon atoms’ nuclei, causing them to recoil and emit electons to be detected. In 2022 July published analysis of 97 days data shows no signs of dark matter particle collisions. This feels a bit disapointment as in 2020, the precessor detector XENON1T found excess of ricocheting electrons. The cause of the surplus was explained by hypothetical lightweight particles that may originate from the sun called solar axions. But the excess wasn’t large enough to be convincing, so more data were needed. No reason found for the previous excess but it may have been a statistical fluke. 

Similarly, the latest experiments of new generation LZ detector (2022 July) found no dark matter. The detector is 1.5 km underground at the Sanford Underground Research Facility with 10 tons of liquid xenon. Using only about 60 days’ worth of data, LZ has already surpassed earlier efforts to pin down WIMPs. LZ is expected to run for about five years, which provides extensive data to find dark matter particles or shrinkens their limits further. 

The ORGAN Experiment, Australia’s first major dark matter detector, recently completed a search for a hypothetical particle called an axion. An axion is believed to convert into a photon in the presence of a strong magnetic field. In a typical haloscope, this magnetic field is generated by using a big electromagnet called a “superconducting solenoid”. The colder the experiment is, the better one can “listen” for faint photons produced during dark matter conversion. In this experiment the resonator was placed in a “dilution refrigerator” cooled down close to the absolute zero temperature, which greatly reduces the noise. An axion of a certain mass will convert into a photon of a certain frequency, or colour.  ORGAN is the most sensitive experiment in its targeted frequency range. Its recent run detected no dark matter signals. This result has set an important exclusion limit on the possible characteristics of axions. In the multi-year plan ORGAN is already preparing the next experiment, which will be more sensitive and target a new, as-yet-unexplored mass range.

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