Feynman Diagrams: Weak Interaction Help

[Monarch]

Hi all

Just a basic question really; I'm at university and have been tutoring someone through a couple of A level physics modules, and I'm covering some basic particle physics at the moment, which is all alright, but I've come to an issue with Feynman diagrams.

Basically, for interactions with either the W or Z bosons, how do you know which one to use? I know these bosons correspond to weak interactions, but is there any kind of methodology for working out which one? For the purpose of the exam back when I did it I just committed the few interactions we needed to know to memory, and this isn't something I've really met at uni yet!

Hope that makes sense

Cheers

 

[Chopin]

The W bosons carry charge, and the Z boson does not, so you should be able to use conservation of charge to determine which boson takes part in any given process.

 

[Monarch]

Thanks for the reply!

That makes sense but I'm struggling to work it out in my head properly. The main ones required are beta minus and beta plus decays. In beta minus, with this diagram
http://www.barnsley.org/penistone-grammar/science/Images/feynman_1.jpg

the exchange particle is a W-, so where does the charge conservation come from (other than the overall conservation with the proton and electron cancelling each other out)?

Apologies if this is basic, it was taught very badly at my school and it's not something I've really had to do since.

 

[Chopin]

Charge conservation happens at every vertex. You have a neutron coming in on the left, which is charge 0. A proton exits, which is of charge +1, so the boson must have charge -1 in order for things to balance. So you know it must be a W-. It then decays into an electron (charge -1), and an electron antineutrino (charge 0), meaning that charge is conserved at that vertex as well.

It wouldn't make sense for the proton-neutron vertex to give off a W+ or a Z, because then the total charge wouldn't be conserved. Similarly, it wouldn't make sense for the W- to decay into a positron + electron neutrino, for the same reason.

 

[paranormal]

Feynman diagrams are a graphical representation of particle interactions in quantum field theory. They are used to visualize and calculate the probabilities of these interactions happening.

In the case of weak interactions, there are two types of Feynman diagrams that correspond to the two bosons involved: the W and Z bosons. The W boson is responsible for charged weak interactions, while the Z boson is responsible for neutral weak interactions.

To determine which boson to use in a Feynman diagram, you need to consider the charges of the particles involved in the interaction. If the particles have opposite charges, then the W boson is involved. If the particles have the same charge, then the Z boson is involved.

For example, in the decay of a neutron into a proton, an electron, and an antineutrino, the neutron (neutral) interacts with the W boson (charged) to produce a positively charged proton and a negatively charged electron. In this case, the W boson is used in the Feynman diagram.

On the other hand, in the decay of a Z boson into an electron and a positron, both particles have the same charge (negative), so the Z boson is used in the Feynman diagram.

Ultimately, the choice of which boson to use in the Feynman diagram depends on the specific interaction being studied. It is important to understand the properties and roles of the W and Z bosons in order to correctly interpret and use Feynman diagrams in weak interactions. I hope this helps clarify things for you.