1932 A new particle, the neutron, is discovered by James Chadwick. There are now three known subatomic particles with mass: the proton, neutron, and electron.
1932 The first antiparticle, the positron, is discovered.
1940s–50s Increasingly powerful particle accelerators—which smash particles together at high speeds—produce large numbers of new subatomic particles.
1964 The discovery of the omega (Ω–) particle confirms the quark model.
2012 The Higgs boson is discovered at CERN, adding weight to the standard model.
Understanding of the structure of the atom has changed dramatically since the end of the 19th century. ...