How to detect nteraction between two massless particles?

[mangothode]

What equipment one can use to detect interaction between two massless particles, such a photons? Is that even possible?
If it is possible, I guess the only thing that one will be able to measure is the difference in energy between particles.

 

[strangerep]

What equipment one can use to detect interaction between two massless particles, such a photons? Is that even possible?

Photon-photon scattering is an extremely weak effect.
Look up "Delbruck scattering"...