In inclusive electron-positron annihilation into hadrons, hard gluon radiation produces a quark, an antiquark and a gluon, giving three resolved particle jets. Observation of such events at PETRA in 1979 provided direct evidence for gluons. The institutional account is www.desy.de/news/news_search/index_eng.html?openDirectAnchor=1643&printversion=1 .
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