Dark Matter, Dirty Xenon, and the Limits of Laboratory Experiments

Laboratory sciences crucially depend on experiments being clean. But what is clean? In this talk, I open up different versions of clean relating to different ontological registers, and trace the material practices of cleaning as they are attuned to experimental specificities. My case is the XENONnT experiment in the Gran Sasso Mountains of Italy which is meant to detect dark matter in the form the hypothetical WIMP – the Weakly Interacting Massive Particle. This experiment is clean when it is ‘free from signals that mimic dark matter’. In practice, such cleanliness has been difficult to achieve – soaps may be radioactive, steel may spread electronegativity, and humans are altogether dangerously filthy. And because, at least thus far, dark matter remains elusive, it is impossible to tell whether the meticulously cleaned detector is adequately clean. Additional cleaning efforts will make the detector sensitive to neutrino particles: a background that cannot be cleaned away. As the experimenters dread the possibility that this means their experiment will end in limbo, other physicists are now trying to detect other hypothetical dark matter particles with other kinds of experiments, requiring other kinds of cleanliness. The XENONnT experiment itself, meanwhile, has had to ensure that it does not interfere with environmental cleanliness, as per the demands of the surrounding society.