A few days ago, I finished reading Richard Feynman's book QED: The Strange Theory of Light and Matter, which I originally alluded to in my posting of April 2, 2005.
Given that I discussed forces and force particles in my April 2 and April 8 postings, I wanted to add some clarifications in these areas based on Feynman's book, while the topic was still fresh.
The first thing I want to say is that Feynman provided the clearest explanation of the weak nuclear force that I've ever seen. In the material of Feynman's that I quote below, he refers to up quarks as "u" quarks and down quarks as "d" quarks (I first introduced up and down quarks in my March 18, 2005 posting). Feynman notes the following, in terms of the weak force's carrier particle, the W:
Quantum chromodynamics and quantum electrodynamics aren't all there is to physics. According to them, a quark cannot change its "flavor": once a u quark, always a u quark; once a d quark, always a d quark. But Nature behaves differently, sometimes. There is a form of radioactivity that happens slowly -- the kind that people worry about leaking out of nuclear reactors -- called beta decay, which involves a neutron changing into a proton. Since a neutron consists of two d's and a u-type quark while a proton is made of two u's and a d, what really happens is that one of the neutron's d-type quarks changes into a u-type quark... Here's how it happens: the d quark emits a new thing like a photon called a W, which has a coupling with an electron and with another new particle called an anti-neutrino... (pp. 139-140).
Further, as noted in the book's caption to Figure 85, "This process [of beta decay] happens relatively slowly, so an intermediate particle (called a "W-intermediate-boson")... was proposed."
Another thing that Feynman's book (pp. 134-135) helped crystallize in my mind is that quarks -- though held together by gluons and thus clearly associated with the strong nuclear force -- also have electromagnetic charges (which are associated with the electromagnetic force).
Specifically, the up quark has the charge +2/3, whereas the down quark's is -1/3. This makes sense because a proton is made up of two up quarks and a down, thus in total yielding the familiar proton charge of +1 (2/3 + 2/3 -1/3). Similarly, a neutron is comprised of two downs and an up, thus yielding the familiar neutral (i.e., zero) overall charge of a neutron (2/3 - 1/3 - 1/3).
Beta decay's conversion of a neutron into a proton, as Feynman notes, really comes down to one down quark changing into an up, the latter having a charge one greater than the former.
According to a web document by Kenneth R. Koehler, as an example of conservation of charge, "the loss of a negative one charge in the form of the W boson has changed the - 1/3 charge on the down quark to the + 2/3 of the up quark."
Thus, the W particle in this context is known as a W- (with a W+ being its antiparticle).
As noted above, the W particle is just an intermediate. Next, according to Koehler, "The neutral neutrino has changed to the negatively charged electron, and the neutral neutron (charge - 1/3 - 1/3 + 2/3) has become the positive proton (charge 2/3 + 2/3 - 1/3)."
As I noted in my April 8 entry, "The force particles of the weak nuclear force are called W and Z particles." Here, according to Feynman, is the origin of the Z particle:
There is another particle, which we could think of as a neutral W, called Zo [a Z, with a subscript zero]. The Zo does not change the charge of a quark... (p. 141).
The above clarifications thus refine our knowledge of the different forces and their carrier particles. I have had to add some complexities to my earlier "watered down" presentations, but by doing so, I think our understanding will be enhanced in the long run.