Particle tracks, coloured photograph. These tracks show the presence of a charmed sigma particle. It decayed too quickly to leave a track, but its presence was inferred from the other tracks. The sigma was formed when a neutrino hit a proton at lower left. Its decay caused the production of six other particles. Three positive pions caused the loop at upper right, the track at bottom right and the furthest left of the tracks at top right. A negative pion left the track going to top left. A muon travelled to top right, while a lambda (not seen) was revealed as it split into two tracks at lower centre. Electrons formed the spirals (left).
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