| 释义 |
▪ I. ‖ lepton1|ˈlɛptɒn|
Pl. lepta |-ə|, erron. leptas.
[Gr. λεπτόν (sc. νόµισµα coin), neut. of λεπτός small.]
a. An ancient Greek coin of the value of about one-fourth of a farthing; the ‘mite’ of the Eng. versions of the N.T.b. The smallest coin (‘centime’) of modern Greece, being the one-hundredth part of a drachma.
1727–41Chambers Cycl. s.v. Coin, Lepton..os.od. 31/336 qrs. Sterl. 1858Merc. Marine Mag. V. 86 Vessels of 20 tons, 50 leptas per ton. 1877C. Geikie Christ lvii. (1879) 687 Among others, came a poor widow, with her two lepta.
▪ II. lepton2 Nuclear Physics.|ˈlɛptɒn|
[f. Gr. λεπτ-ός small, slight, slender + -on1.]
Any of the sub-atomic particles that do not participate in the strong interaction and have a mass less than that of a nucleon and a half-integral spin (viz. the electron, the muon, and the neutrinos, and their anti-particles); in recent use extended to include any other (hypothetical) particle, of whatever mass, which does not participate in the strong interaction. (Orig. introduced in a wider sense: see quot. 1948.)
1948L. 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. 1959Sci. News. LII. 101 A similar conservation law holds for leptons, a group of particles including neutrinos, electrons, and muons. 1964Cambr. Rev. 24 Oct. 53/1 The..equality of the Fermi coupling constant for many different particles, baryons, mesons and leptons. 1967New Scientist 8 June 578/1 These, the leptons, consist of the electron, the muon, two types of the massless, chargeless neutrino..and the anti⁓particles of these four. 1969R. E. Marshak et al. Theory Weak Interactions Particle Physics i. 2 The fact that the weak interaction takes place at approximately the same level of strength between leptons.., between leptons and hadrons.., and between hadrons is a major distinguishing feature of the weak interaction. Ibid. 7 The names lepton, meson, and baryon were originally invented to denote light, intermediate mass, and heavy particles respectively, but 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. 1971New Scientist 17 June 669/3 If heavy leptons..exist, Pontecorvo argues that they must have neutrinos also. 1973Sci. Amer. Oct. 111/2 There may well exist a spectrum of leptons of increasing mass. The heavy leptons, if they exist, could be produced, like muons, in pairs in electron-positron annihilation reactions. Ibid. Nov. 36/2 The few particles that feel only weak or electromagnetic forces are classed as leptons. Electrons, muons and neutrinos are the only known leptons.
b. lepton number, a quantum number assigned to sub-atomic particles that is {pm} 1 for leptons and 0 for other particles and is conserved in all known interactions.
1958Physical Rev. CX. 1483/2 Such selection rules..consist of giving opposite lepton numbers to µ- and e-. 1967L. M. Lederman in E. H. S. Burhop High Energy Physics II. 342 Conservation of lepton number now is a matter of Nµ and Ne being separately conserved. 1973Sci. Amer. Aug. 33/2 The preference of the neutrino for the electron and of the antineutrino for the positron has been included in the theory of weak interactions by assigning a..lepton number to the various weakly interacting particles. The convention is that the electron and the neutrino have a lepton number of + 1, whereas their anti⁓particles, the positron and the antineutrino, have a lepton number of - 1.
Hence lepˈtonic a., of, pertaining to, or involving leptons; leptonic number = lepton number.
1957Ann. Physics. II. 422 Particles labelled by leptonic charge and electrical charge permit a complete identification with the known leptons. 1958Proc. 2nd Internat. Conf. Peaceful Uses Atomic Energy (United Nations) 53 The law of conservation of leptons..states that if a leptonic number is assigned to each particle then the sum of leptonic numbers must be conserved in all reactions. 1969Nature 23 Aug. 780/2 The λ hyperon has leptonic decays of a very similar kind to those of the σ. |