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In 1987 the ARGUS detector of the DORIS storage ring was the first place where the conversion of a B-meson into its antiparticle, the anti-B-meson was observed.

From this one could conclude that it was possible, for the second-heaviest quark-the bottom-quark-under certain circumstances to convert into a different quark.

One could also conclude from this that the unknown sixth quark-the top quark-had to possess a huge mass.

The top quark was found eventually in 1995 at the Fermilab in the USA.