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Unlike protons and neutrons, which are made of three quarks, mesons are made of one quark and one antiquark.

A beam of positive pions—lightweight particles made from an up quark and a down antiquark—decay into muons and muon neutrinos.

Pionic helium is here: a helium atom in which one of the two electrons has been replaced by a negative pion, a composite particle made of one quark and one antiquark.

They belong to the family of subatomic particles known as mesons, which are made up of a quark and an antiquark; quarks are the particles that make up protons and neutrons.

Of these, only a few hundred collisions simultaneously produced a Higgs boson and a top quark/antiquark pair.