Historic bubble chamber image which led to the discovery of the "charmed baryon," a three-quark particle. The baryon itself decayed too quickly to be captured on film, but its presence can be deduced from the the other observable events shown. A neutrino entered from the lower right (dashed line) and collided with a proton, producing five charged particles - one negative muon, three positive pions, and one negative pion - and a neutral lambda. The momenta and angles of the tracks taken together imply that the lambda and the four pions came from the decay of a charmed sigma particle, with a mass of about 2.4 billion electron volts.