BROOKHAVEN NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY BROOKHAVEN NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY
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Production & decay of charmed sigma particle. In this coloured bubble chamber photo, taken in 1974 at the Brookhaven National Laboratory, USA, the sigma (containing a charm quark) lives too briefly to be seen but is inferred from other particles. A neutrino enters unseen at bottom & collides with a proton in the bubble chamber liquid, producing a negative muon (red) & the sigma. The sigma decays to one negative pion (green, left), three positive pions (blue), & an unseen neutral lambda which betrays itself when it decays to a proton (purple) & a negative pion (green, right). The muon & one of the pions knock out atomic electrons which produce the two spiral tracks (yellow).
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