HX OF QNTM PHYSICS 1936 MUON, 1968 QUARK FTHR X DTRb

Make it up, break it down

The history of physics often involves finding that fundamental particles are nothing of the sort

1897

J. J. Thompson discovers electrons by deflecting cathode rays in an electric field. It is the first subatomic particle ever discovered

1908

Hans Geiger and Ernest Marsden find that some positively charged particles can pass through gold foil, suggesting the gold atoms are mostly empty space with a small nucleus

1917

Geiger and Marsden’s boss, Ernest Rutherford, finds that the nitrogen nucleus contains smaller particles called protons

1932

James Chadwick discovers the neutron. Now all three components of the atom – electron, proton and neutron – are unmasked

1936

Carl Anderson and Seth Neddermeyer find that particles in cosmic rays curve less sharply in an electric field than electrons. These heavier cousins of the electron are called muons

1968

Scattering experiments at SLAC reveal that protons contain smaller particles, later confirmed as quarks

1974

Martin Lewis Perl and colleagues discover the tau, an even heavier version of the electron

1980s

The standard model attains roughly its present form, with quarks and leptons as the indivisible particles of matter

2012

The Higgs boson is discovered at CERN

2014

Particles called B mesons decay to leptons in ways that appear to contradict the standard model. One explanation is that leptons, too, may contain smaller particles that we haven’t yet seen