The title is slightly misleading, also in usual physicist speak right. The kind of particle here are made up of four quarks, and as far as I know were somewhat

The title is slightly misleading, also in usual physicist speak right. The kind of particle here are made up of four quarks, and as far as I know were somewhat expected. The underlying theory, QCD, predicts that free particles (hadrons)^1 are bound states of quarks, and in this case bound states of two quarks and two anti-quarks. (Wether we should call everything we see in a collider a particle is a question, which I happily leave for philosophers to answer.) ^1 A hadron is is made of quarks and gluons, which can only exist as bound states, such that they have no net strong charge. Contrast this with a lepton like the electron, that has no strong charge and can consequently exist as a free particle.