Feynman rules and decay process

In summary, the first process of cc decaying into tau++tau- is not possible through the strong force, but may be possible through electroweak interactions. The second process of cc decaying into cu and cu is kinematically forbidden due to energy conservation. However, if the particles have enough energy, it is allowed. Additionally, for the second process, one of the initial particles can release a gluon which can produce a pair of u quarks.
  • #1
jc09
45
0
Hi I need help to understand Feynman rules for decay for exams. In past paper there is the following question as whether the following are allowed.

cc decays to tau++tau-. From What I can see this is possible via the strong force is this correct?

The next is cc decays to cu and cu. From what I can this this can't happen but is this correct?

In these question c is the antiparticle
 
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  • #2
The second process can happen.
One of the initial particles, say c, can release a gluon which can produce a pair of u quarks.
 
  • #3
jc09 said:
Hi I need help to understand Feynman rules for decay for exams. In past paper there is the following question as whether the following are allowed.

cc decays to tau++tau-. From What I can see this is possible via the strong force is this correct?

This is certainly wrong: the tau is a lepton and leptons do not interact via strong force.
IMHO, this decay is possible via electroweak interactions: c and c-bar annihilate into a virtual Z-boson or photon, which in turn decays into the pair of leptons.

jc09 said:
The next is cc decays to cu and cu. From what I can this this can't happen but is this correct?

In these question c is the antiparticle

This is kinematically forbidden (energy conservation): the outgoing particles would be in sum heavier than the decay parent.
 
  • #4
As far as ccbar goes, it depends on what you mean by "decay". If both are at rest with respect to each other, then ccbar -> c ubar + u cbar is forbidden. If they have enough energy to overcome the 2m_u barrier you need to start that reaction, then you're fine and it's allowed.
 

1. What are Feynman rules?

Feynman rules are a set of mathematical rules used in quantum field theory to calculate the probability of particle interactions. They were developed by the physicist Richard Feynman and are based on his diagrams, which represent the possible paths of particles in a given interaction.

2. How are Feynman rules used in the decay process?

Feynman rules are used to calculate the Feynman diagrams associated with particle decay. These diagrams show the possible paths of particles involved in the decay and can be used to determine the probability of the decay occurring.

3. What is the role of Feynman rules in particle physics?

Feynman rules are essential in particle physics as they provide a framework for calculating the probability of particle interactions and decay. They allow physicists to make predictions about the behavior of subatomic particles and have been crucial in the development of the Standard Model of particle physics.

4. How do Feynman rules differ from other mathematical techniques used in quantum field theory?

Feynman rules are based on visual diagrams and are often considered more intuitive than other mathematical techniques used in quantum field theory. They also allow for easier calculations of complex interactions involving multiple particles.

5. Can Feynman rules be applied to all types of particle interactions?

Yes, Feynman rules can be applied to all types of particle interactions, including strong, weak, and electromagnetic interactions. They provide a universal framework for calculating the probability of these interactions and have been successfully used in various experiments and theoretical models.

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