|Hideki Yukawa, Cecil Powell, César Lattes, Giuseppe Occhialini particle physics|
Hideki Yukawa predicted that an unstable particle would be found heavier than an electron and lighter than a proton to carry the nuclear force that holds atomic nuclei together. We name these after the Greek μέσος meaning “intermediate.” It took thirteen years and the end of the war for the first meson to be found. Investigating the products of cosmic rays on mountain peaks, Powell, Lattes, and Occhialini discovered the pi meson, or pion.
List of mesons
About 140 types of mesons, all being virtual composites of a quark and an antiquark bound by strong interactions, but differing in spin, parity, charge, mass, angular momentum, strangeness, charm, beauty, and lifetime, including pion, eta meson, eta prime meson, bottom eta meson, charmed eta meson, charmed rho meson, neutral rho meson, omega meson, phi rho meson, upsilon meson, and kaon. Kaon or K meson is any of four mesons with different strangeness, composed of a strange quark or strange antiquark with an up or down quark or antiquark.
The cosmic ray connection
Pions were discovered as tracks in photographic plates exposed for long periods at Pic du Midi de Bigorre in the Pyrenees and at Chacaltaya in the Andes. Kaons, too, were discovered as products of cosmic rays. At first, scientists thought muons were mesons. Its discoverers, Carl David Anderson and Seth Neddermeyer, had lifelong interests in studying the effects of cosmic rays.