Constraining new coloured matter from the ratio of 3- to 2-jets cross   sections at the LHC
  The Large Hadron Collider experiments are probing the evolution of the strong coupling $\alpha_s$ up to the TeV scale. We show how the ratio of 3- to 2-jets cross sections is affected by the presence of new physics and argue that it can be used to place a model-independent bound on new particles carrying QCD color charge. The current data potentially constrains such states to be heavier than a few hundred GeVs. 
Diego Becciolini, Marc Gillioz, Marco Nardecchia, Francesco Sannino,   Michael Spannowsky
hep-ph hep-ex