W and Z bosons weak-force boson particle. Thus, this interaction requires a Z boson. These bosons are among the heavyweights of the elementary particles. With masses of and , respectively, the W and Z bosons are almost 80 times as massive as the proton – heavier, even, than entire iron atoms. Their high masses limit the range of the weak interaction. By way of contrast, the photon is the force carrier of the electromagnetic force and has zero mass, consistent with the infinite range of electromagnetism; the hypothetical graviton is also expected to have zero mass. (Although gluons are also presumed to have zero
Elementary charge known elementary particles, including quarks, have charges that are integer multiples of "e". Therefore, one can say that the "quantum of charge" is "e". In this case, one says that the "elementary charge" is three times as large as the "quantum of charge". On the other hand, all "isolatable" particles have charges that are integer multiples of "e". (Quarks cannot be isolated: they only exist in collective states like protons that have total charges that are integer multiples of "e".) Therefore, one can say that the "quantum of charge" is "e", with the proviso that quarks are not to be