1921 Chem. Abstr. 15 983 Leptonology..is the name proposed by R. [= F. Rinne] to designate stereochemistry, stereophysics and crystal structure as a group. The units dealt with (atoms, ions, mols. and even electrons) are called leptons.

1927 Proc. Geologists' Assoc. 38 542 The difference between adsorption..and a true valency link..lies only in the degree of ionisation and in the size and arrangement of the ultimate structural units (leptons).

1952 J. R. Partington Adv. Treat. Physical Chem. III. 134 Rinne proposed the atomic volume divided by Avogadro's number..as the lepton (λεπτ-ος, fine, or delicate), and wished to call the study of atoms, molecules, ions, and electrons, ‘leptonology’. Avogadro's number is then 6 x 10²³ leptons.

1948 L. Rosenfeld Nucl. Forces p. xvii This can be achieved..by postulating a special kind of interaction between a nucleon and a pair of light particles, or leptons, consisting of an electron and a neutrino. [Note] Following a suggestion of Prof. C. Møller, I adopt—as a pendant to ‘nucleon’—the denomination ‘lepton’ (from λεπτός, small, thin, delicate) to denote a particle of small mass, irrespective of its charge.

1949 Physica 15 863 The nuclear matrix element disappears..for each of the five invariants of the Dirac theory which can be chosen for the nucleon-lepton interaction.

1956 Nucl. Physics 1 658 They are powerless in characterizing the decay interaction of heavy mesons into leptons.

1969 R. E. Marshak et al. Theory Weak Interactions Particle Physics i. 7 We now know that the particles in each of the three classes share certain important properties in common; both the leptons and baryons are fermions..whereas the mesons are bosons. However, of greatest importance is the presence of the strong interaction for the meson and baryon classes but not for the lepton class.

1973 Sci. Amer. Oct. 111/2 There may well exist a spectrum of leptons of increasing mass.

1987 R. A. Thompson & L. S. Thompson Egoshell ii. C-iv. 157 Quarks and leptons are considered the building blocks of the universe.

2006 L. Smolin Trouble with Physics v. 72 The most elegant and sparse theory hypothesizes that Higgs bosons are bound states of very heavy quarks or leptons.

1957 Nucl. Physics 3 599 The results depend closely on whether the attractive postulate of the conservation of fermion numbers (lepton numbers as well as baryon numbers) does hold or not.

1967 L. M. Lederman in E. H. S. Burhop High Energy Physics II. 342 Conservation of lepton number now is a matter of N_μ and N_e being separately conserved.

2008 H. R. Quinn & Y. Nir Myst. Missing Antimatter xii. 131 For the weak interactions, the symmetries related to baryon and lepton number are not exactly respected.