Short question. I know that COLLIDING beams are much more effective than when moving particle hits a target in observers reference frame. That is why they make a collider. However, when Oh My God particles are observed they actually hit something that something does not move. So, when we say that we cant reproduce Cosmic Rays energies on LHC, what exactly do we compare? What reference frame do we use? Do we compare energies per particle in our rest frame (ignoring that it is a collider) or not?