Strong and weak interactions in nuclear physics

In summary, the conversation discusses how to determine whether a process involves a strong or weak interaction by looking at the quark content, checking for conservation of quark numbers and other properties, and using shortcuts such as the presence of photons or neutrinos. The conversation also clarifies that isospin can be violated in weak interactions.
  • #1
rayman123
152
0

Homework Statement



How do we determine whether we have a strong or a weak interaction? (for the following processes)

For example we have a reaction
[tex] K^{-}+p\Rightarrow \Xi^{-}+K^{+}[/tex]

or another example
[tex]K^{+}\Rightarrow \pi^{+}+\pi^{0}[/tex]

thanks!
 
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  • #2
Start by looking up the quark content of the individual particles.
 
  • #3
for the first one is
[tex] u\overline{s}+uud\Rightarrow dss+u\overline{s}[/tex]
but I still do not know how from this I can determine the type of interaction
 
  • #4
That can't be right. You have the same quarks for K+ and K-.
 
  • #5
according to my physics handbook Carl Nordling both these kaons have the same content (the same quarks)...maybe it is an error? Or maybe it follows some kind of a notation system?
From particle data group I found for [tex] K^{+} (u \overline{s})[/tex] and for [tex] K^{-} (\overline{u}s)[/tex]
 
  • #6
They're a particle-antiparticle pair. Your handbook probably just lists what the quarks are for the particle. Just swap quark for antiquark and vice versa to figure out what the antiparticle is. So now you have

[tex]\overline{u}s+uud \Rightarrow dss+u\overline{s}[/tex]

You just have to check if the process is consistent with the various interactions. For example, strong interactions will not change quark numbers. If quark numbers aren't conserved in a process, you can rule out the strong interaction. Another approach is to draw the Feynman diagram for the process. You just need to know what vertices are allowed.

A few shortcuts you can take:

1. A photon only interacts electromagnetically, so if a photon is present, the process is electromagnetic.
2. Similarly, the neutrino only interacts via the weak force, so if a neutrino is present, it's a weak interaction.
3. Leptons don't carry color charge, so if a lepton is involved, it can't be a strong interaction.
 
  • #7
I have checked and strangeness is conserved, baryon nr is conserved, charge nr is conserved, isospin is conserved the only thing which is not conserved is the projection of the isospin. Does this rule the strong interaction out and we are left with the possible weak interaction?
 
  • #8
It looks like I3 is conserved to me. Why did you decide it wasn't?
 
  • #9
hm maybe I made mistake...Yes you are right, I got on the left hand side of the reaction: -1/2,+1/2
on the left hand side: -1/2, +1/2
It is just my physics handbook which is a bit confusing...but I think I figured out how the system works now
so I guess we can write that because there is not violation of any of above numbers and the interaction is strong
 
  • #10
I have another question, can [tex] I_{3}[/tex] be violated in case of the weak interaction?
 
  • #11
Yeah, it looks like a strong interaction to me.
 
  • #12
rayman123 said:
I have another question, can [tex] I_{3}[/tex] be violated in case of the weak interaction?
Yes, the weak interaction can change quark flavors, so isospin isn't always conserved.
 

1. What are strong and weak interactions in nuclear physics?

The strong and weak interactions are fundamental forces that govern the behavior of subatomic particles within the nucleus of an atom. The strong interaction is responsible for holding the nucleus together, while the weak interaction is involved in radioactive decay.

2. How do strong and weak interactions differ from each other?

The main difference between strong and weak interactions is their strength. The strong interaction is much stronger than the weak interaction, which is why it is able to hold the nucleus together. Additionally, the strong interaction only acts on particles within the nucleus, while the weak interaction can act on particles both inside and outside the nucleus.

3. How do strong and weak interactions contribute to nuclear stability?

The strong interaction is responsible for binding the protons and neutrons together in the nucleus, creating a stable structure. Without this strong force, the repulsive forces between the positively charged protons would cause the nucleus to break apart. The weak interaction helps to maintain nuclear stability by balancing the number of protons and neutrons in the nucleus, through processes such as beta decay.

4. Can strong and weak interactions be observed in everyday life?

While strong and weak interactions may not be directly observable in everyday life, their effects can be seen in the behavior of atoms and subatomic particles. For example, the decay of radioactive materials is a result of the weak interaction, and nuclear energy is harnessed through the manipulation of the strong interaction.

5. How do scientists study strong and weak interactions?

Scientists use a variety of techniques and experiments, such as particle accelerators and nuclear reactors, to study the behavior of subatomic particles and the interactions between them. These experiments allow scientists to understand the fundamental forces that govern the behavior of matter on a microscopic level.

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