Beta Decay Q&A: Quarks, W Bosons & More

[To the lab]

In beta decay, is the W boson created by the change of a quark or does it cause the change? Also, I don't fully understand where the W bosons come from or how they are created. If someone could please explain this to me, I'm very confused.

 

[Drakkith]

In beta decay, is the W boson created by the change of a quark or does it cause the change?

The weak interaction allows an down quark to convert into an up quark by emitting an w- boson, which then decays into an electron and an electron antineutrino. The w- boson is merely an intermediate product of the decay and is not the cause.

Also, I don't fully understand where the W bosons come from or how they are created. If someone could please explain this to me, I'm very confused.

That's a good question. Fundamental particles don't really come from anywhere in the normal way of thinking about it. We don't break open fundamental particles and see a bunch of other particles emerge, nor do we take smaller particles and put them together to create another particle. (Well, we do, but those aren't fundamental particles) These fundamental particles didn't exist prior to their creation. They can be created through various interactions and decay processes as long as certain requirements are met. (Such as having enough energy to convert to the mass of the particle) Note that in quantum field theories, particles are merely excited states of different underlying fields. So the "creation" of a particle might be viewed as transferring energy to this field. This would be analogous to the creation of a photon by accelerating an electrically charged particle.

The difference is that the electromagnetic interaction (another name for the EM force) is responsible for transferring this energy to the EM field and creating the photon while the weak interaction is responsible for changing particles from one type to another and creating the w- boson.

 

[To the lab]

Thanks for the reply! One question: can this be reproduced in a lab?

 

[jtbell]

Can what be reproduced in a lab?

 

[To the lab]

The release of a W boson through beta decay, which is to say, can it be induced?

 

[Vanadium 50]

There is no "release of a W boson". This is a calculational trick, but at the end, all that is released is the electron and antineutrino.

 

[jtbell]

The release of a W boson through beta decay, which is to say, can it be induced?

The W in beta decay is "virtual," not "real." In order to produce a real W boson, enough energy has to be supplied to create the mass of a real W, which is much much greater than the mass of a neutron. (Virtual particles generally don't have the same mass as real ones.)

Real W's have been produced in high-energy accelerator experiments at CERN and Fermilab as far back as the mid 1980s. Carlo Rubbia won a Nobel Prize for the first experiment that did this, IIRC.

 

[Bill_K]

The W in beta decay is "virtual," not "real." In order to produce a real W boson, enough energy has to be supplied to create the mass of a real W, which is much much greater than the mass of a neutron. (Virtual particles generally don't have the same mass as real ones.)

Real W's have been produced in high-energy accelerator experiments at CERN and Fermilab as far back as the mid 1980s. Carlo Rubbia won a Nobel Prize for the first experiment that did this, IIRC.

The W bosons that Rubbia produced were virtual also, the difference was that they had enough energy that their rest mass could be determined. With a lifetime of 10^-25 sec and a width of about 2 GeV, W bosons are always off the mass shell.

 

[mfb]

The W bosons that Rubbia produced were virtual also, the difference was that they had enough energy that their rest mass could be determined. With a lifetime of 10^-25 sec and a width of about 2 GeV, W bosons are always off the mass shell.

With that argument, no unstable particle would ever be real, including muons, pions, or even radioactive nuclei...
It is a possible way to see it, but it is certainly uncommon and leads to strange effects.