TOMASZ BARSZCZAK / SUPER-KAMIOKANDE COLLABORATION / SCIENCE PHOTO LIBRARY TOMASZ BARSZCZAK / SUPER-KAMIOKANDE COLLABORATION / SCIENCE PHOTO LIBRARY
A cosmic ray muon creates an arrow of light in the Super-Kamiokande detector (SK) located 1000 metres under Mt Ikenoyama, Japan. A cylinder of ultra- clean water 41m tall and 39m in diameter, SK is lined with 11200 phototubes to record Cerenkov light produced when charged subatomic particles travel through water faster than light does. Here, coloured dots show tubes that have recorded light. The red end of the spectrum indicates the earliest light to arrive. The muon entered through the bottom of the cylinder, where the earliest light appears, and exited 120 nanoseconds later through the side wall near the centre of the image.
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