Measurement of dijet azimuthal decorrelations in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector and determination of the strong coupling

TL;DR

This paper measures dijet azimuthal decorrelations in proton-proton collisions at 8 TeV using ATLAS data, compares results with QCD predictions, and determines the strong coupling constant across a wide momentum transfer range.

Contribution

It provides the first detailed measurement of $R_{ riangle ext{phi}}$ and extracts the strong coupling constant from high-energy dijet events.

Findings

The data agree well with next-to-leading order QCD predictions.

The strong coupling constant at the Z boson mass is measured as $oxed{0.1127^{+0.0063}_{-0.0027}}$.

The running of $oldsymbol{ ext{α}_ ext{S}}$ is studied from 260 GeV to above 1.6 TeV.

Abstract

A measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity $R_{\Delta \phi}$. The quantity $R_{\Delta \phi}$ 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 $\Delta \phi_\mathrm{max}$. The quantity $R_{\Delta \phi}$ is measured in proton--proton collisions at $\sqrt{s}=$8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and $\Delta \phi_\mathrm{max}$. The measurement uses an event sample corresponding to an integrated luminosity of 20.2 fb$^{-1}$ collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for non-perturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling $\alpha_{\mathrm{S}}$ 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 $\alpha_{\mathrm{S}}(m_{Z}) = 0.1127^{+0.0063}_{-0.0027}$.