Exotic annihilation products?

[Gilded]

The antimatter thread at Astronomy & Cosmology reminded me of something. Specifically, why is the creation of heavy particles like W bosons and such favored over photons in high energy annihilations? Is there some sort of energy limit after which all net energy can't just be "dumped" into photons?

[Severian]

Which annihilations are you talking about? If you go to really high energies, the mass difference between the photon and Z become negligible, so the extra mass of the W/Z doesn't matter and all that will determine the decay is the couplings of the particles.

 

At low energies, significantly below the W and Z mass you will not produce the W and Z mass much because you just don't have enough energy to make their mass (they have to be very off-shell).

 

However, if the annihilation happens at around the energy of the W or Z mass, then you have what is called resonant production. In essence you have hit the resonant frequency for creating the W or Z, so you make a lot of them.

[Gilded]

Which annihilations are you talking about?

 

High (GeV range and upwards) energy electron-positron annihilations in general. I had read somewhere that particles like W bosons can be produced instead of photons when the amount of energy increases, I wasn't quite sure about exact figures.

 

At low energies, significantly below the W and Z mass you will not produce the W and Z mass much because you just don't have enough energy to make their mass (they have to be very off-shell).

 

Yes, that I had gathered.

 

However, if the annihilation happens at around the energy of the W or Z mass, then you have what is called resonant production. In essence you have hit the resonant frequency for creating the W or Z, so you make a lot of them.

 

Hmm I see. But photons can still be created at these energies, it's just very improbable compared to heavy (as in having non-zero proper mass) boson production, right?

[Severian]

Hmm I see. But photons can still be created at these energies, it's just very improbable compared to heavy (as in having non-zero proper mass) boson production, right?

 

Yes. The probability goes down with the square of the energy. This is because you are moving away from the photon's mass-shell which is at zero (since the photons have zero mass).