According to the Hoop Conjecture, if one can pack a sufficient amount of energy in a small enough region, black holes can be formed. The work on gravitational interaction between high energy particles indicate that classical black holes can be formed if the impact parameter is sufficiently small. An article by Xavier Calmet gives the estimate $b=3.2\mu$ where b is the impact parameter and $\mu$ is the center of mass energy.
So my question is - what determines how small the impact parameter can be? What prevents the formation of classical black holes (mass>>Planck mass) in LHC?
I know there was a lot of work about 'mini black holes' in the context of theories with large extra dimensions. I'm asking this for classical black holes in usual GR + standard model.