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The XENONnT experiment set a record for the elusiveness of dark matter.
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Dark matter is the invisible glue that keeps galaxies from falling apart. Back in the 1930s, Fritz Zwicky suspected its existence, and in the 1970s Vera Rubin proved that without it, stars would fly apart. This substance barely interacts with ordinary matter: it doesn't shine and passes through atoms as if through empty space.
The XENONnT detector is a lake of liquid xenon in an Italian cave, shielded by a thick layer of rock. When a dark matter particle does smash into a nucleus, an electrical ripple runs through the liquid — like a pebble dropped in a dead calm. For 579 days, physicists stared into this stillness, working blind so as not to fool themselves.
No splashes were found. But the silence drew a map of forbidden territory: we now know what interactions dark matter definitely doesn't have. The limit is such that a particle could pass through thousands of light-years of lead without a single touch. The experiment hit the neutrino rain — soon the background of ubiquitous neutrinos will merge with the ripples, and hunting blind will become impossible. This tells us that the Standard Model is incomplete, and the next detector must tell a stone from raindrops.
To avoid self-deception, physicists worked blind: until the analysis was complete, they didn't know which part of the data might contain signals. This 'blind analysis' protects against random coincidences.
