Measurement of the ratio of the inclusive 3-jet cross section to the inclusive 2-jet cross section in pp collisions at √s = 7 TeV and first determination of the strong coupling constant in the TeV range

A measurement is presented of the ratio of the inclusive 3-jet cross section to the inclusive 2-jet cross section as a function of the average transverse momentum, ⟨pT1,2⟩, of the two leading jets in the event. The data sample was collected during 2011 at a proton–proton centre-of-mass energy of 7 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 5.0 fb−1. The strong coupling constant at the scale of the Z boson mass is determined to be α S (M Z)=0.1148±0.0014 (exp.)±0.0018 (PDF)±0.0050(theory), by comparing the ratio in the range 0.42<⟨pT1,2⟩