In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

A baryon state that decays into a delta baryon and one of these, or one or two nucleons and one of these, is the Roper resonance. The energy of cosmic rays is bounded at around five times ten to the nineteen eV because collisions with CMB photons would produce these particles at higher energies. These particles are the standard triplet representation of SU(2) isospin symmetry. One type of these usually decays into a muon and its neutrino, and the other usually forms two photons or can form a photon, electron, and positron in Dalitz decay. Its charged versions are the up antidown and the down antiup. For 10 points, name these first-generation mesons, the lightest.
Science