Feynman rules and decay process

[jc09]

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

 

[Rick88]

The second process can happen.
One of the initial particles, say c, can release a gluon which can produce a pair of u quarks.

 

[Hawkwind]

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.

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.

 

[chrispb]

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.