The Weak Force

One of the four fundamental forces, the weak interaction involves the exchange of the intermediate vector bosons, the W and the Z. Since the mass of these particles is on the order of 80 GeV, the uncertainty principle dictates a range of about 10-18 meters which is about 0.1% of the diameter of a proton. The weak interaction changes one flavor of quark into another. It is crucial to the structure of the universe in that 1. The sun would not burn without it since the weak interaction causes the transmutation p -> n so that deuterium can form and deuterium fusion can take place. 2. It is necessary for the buildup of heavy nuclei. The role of the weak force in the transmutation of quarks makes it the interaction involved in many decays of nuclear particles which require a change of a quark from one flavor to another. It was in radioactive decay such as beta decay that the existence of the weak interaction was first revealed. The weak interaction is the only process in which a quark can change to another quark, or a lepton to another lepton - the so-called "flavor changes". "By emitting a W boson one kind of fermion can change into another kind: a down quark can spit out a W- and change into an up quark. .. None of the other forces can change the identity of the particles they interact with." (Carroll) The discovery of the W and Z particles in 1983 was hailed as a confirmation of the theories which connect the weak force to the electromagnetic force in electroweak unification. The weak interaction acts between both quarks and leptons, whereas the strong force does not act between leptons. "Leptons have no color, so they do not participate in the strong interactions; neutrinos have no charge, so they experience no electromagnetic forces; but all of them join in the weak interactions."(Griffiths) Show Feynmann diagrams

Index



Fundamental force concepts



Reference

Griffiths

Ch 2



Carroll

The Particle at the End.., Ch 2