在南达科他州黑山地下千米探寻暗物质
In the labyrinthine corridors of the former Homestake gold mine, now reborn as the Sanford Underground Research Facility, a different kind of treasure hunt unfolds. A mile of Precambrian rock—quartz, schist, and amphibolite—absorbs the cosmic-ray muons that would otherwise swamp the delicate detectors arrayed in the cool, dry chambers below. Here, physicists from an international collaboration wager that dark matter, the invisible scaffolding of the cosmos, might barely nudge a nucleus of liquid xenon in the LUX-ZEPLIN experiment, a cryogenic vat of unparalleled purity.
The rationale for burrowing so deep is both pragmatic and humbling. Cosmic rays, the high-energy debris from distant supernovae and the sun, shower the Earth’s surface with billions of muons per square meter each year. These particles create a deafening background noise for any detector seeking the faint recoil signature of a weakly interacting massive particle (WIMP). A kilometer of rock acts as a natural filter, reducing the muon flux by a factor of a million. Yet even in this quiet sanctuary, the expected event rate for dark matter is vanishingly small—perhaps a handful of interactions per year.
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