Measurements of dijet azimuthal decorrelations and extraction of $alpha_S$ at ATLAS

The production of jets at hadron colliders provides stringent tests of perturbative QCD. We present a measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations, using the quantity $RΔϕ$. This quantity specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter $Δϕ_{max}$. $R_{Δϕ}$ is measured in proton-proton collisions at $√s=$8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and $Δϕ_{max}$. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for non-perturbative effects describe the data well in the whole kinematic region. The data are used to determine the strong coupling $\alpha_S$ and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. An analysis that combines data at all momentum transfers results in $\alpha_s(m_Z)=0.1127_{-0.0027}^{+0.0063}$.