An up quark decays into a W + boson and a down quark. flavour changing of quarks or leptons is allowed, as long as these three rules are obeyed.įigure 9 A beta-plus decay process involves the creation and disappearance of a W + boson.the number of leptons minus the number of antileptons is conserved.the number of quarks minus the number of antiquarks is conserved.Notice also that the production of a charged lepton is always accompanied by the corresponding flavour of neutrino. If they were not, then the rule of lepton conservation would be violated. This is the explanation for why neutrinos and antineutrinos are produced in beta-decays. In the example of beta-minus decay, there are no leptons initially present, and after the interaction there is one lepton and one antilepton – a net result of zero again. In weak interactions, the total number of quarks minus the total number of antiquarks is the same both before and after the interaction. The W − boson subsequently decays into an electron and an electron antineutrino. A down quark decays into a W − boson and an up quark. In accordance with the energy–time uncertainty principle it therefore rapidly decays to produce an electron and an electron antineutrino, setting the energy accounts straight.įigure 8 A beta-minus decay process involves the creation and disappearance of a W − boson. The mass energy of the W − boson is about 80 GeV, so it cannot possibly emerge from the nucleus as there are only a few MeV of energy available. At the quark level, the explanation is that a down quark, d, with a negative electric charge equal to one-third that of an electron is transformed into an up quark, u, with a positive electric charge equal to two-thirds that of a proton.Ī W − boson is emitted with one unit of negative electric charge, so conserving electric charge in the process. At most, a few MeV of energy are released in this process, corresponding to the difference in mass between the original nucleus and the resultant nucleus. The Universe would be an impossibly boring place without them.Īs you know, the beta-minus decay of a nucleus occurs when a neutron turns into a proton, with the emission of an electron and an electron antineutrino. In weak interactions, W and Z bosons interact with each other, as well as with all quarks and leptons. The two (charged) W bosons each have a mass of about 80 GeV/ c 2 whereas the (neutral) Z boson has a mass of about 90 GeV/ c 2. In fact, there are two types of W boson, one with negative electric charge, the W − boson, and one with positive electric charge, the W + boson. In the same way that photons and gluons are the quanta involved in electromagnetic and strong interactions, respectively, weak interactions involve other quanta – known as W bosons and Z bosons.
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