Determination of the strong coupling constant α s from transverse energy-energy correlations in multijet events at s = 8 TeV using the ATLAS detector

Abstract

Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to $\sqrt{s}=8\text{TeV}$ proton-proton collisions with an integrated luminosity of 20.2 ${\text{fb}}^{-1}$ . The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of ${\alpha }_s\left(\mu \right)$ predicted in QCD up to scales over $1\text{TeV}$ . A global fit to the transverse energy-energy correlation distributions yields ${\alpha }_s\left(m_Z\right)=0.1162\pm 0.0011\text{(exp.)}{}_{-0.0070}^{+0.0084}\text{(theo.)}$ , while a global fit to the asymmetry distributions yields a value of ${\alpha }_s\left(m_Z\right)=0.1196\pm 0.0013\text{(exp.)}{}_{-0.0045}^{+0.0075}\text{(theo.)}$ .

Fig. 1

Detector-level distributions for the TEEC (top) and ATEEC functions (bottom) for the first and the last $H_{\mathrm{T}2}$ intervals chosen in this analysis, together with MC predictions from Pythia8, Herwig++ and Sherpa. The total uncertainty, including statistical and detector experimental sources, i.e. those not related to unfolding corrections, is also indicated using an error bar for the distributions and a green-shaded band for the ratios. The systematic uncertainties are discussed in Sect. 7

Fig. 2

Systematic uncertainties in the measured TEEC (top) and ATEEC distributions (bottom) for the first and the last bins in $H_{\mathrm{T}2}$. The total uncertainty is below 5% in all bins of the TEEC distributions

Fig. 3

Particle-level distributions for the TEEC functions in each of the $H_{\mathrm{T}2}$ intervals chosen in this analysis, together with MC predictions from Pythia8, Herwig++ and Sherpa. The total uncertainty, including statistical and other experimental sources is also indicated using an error bar for the distributions and a green-shaded band for the ratios

Fig. 4

Particle-level distributions for the ATEEC functions in each of the $H_{\mathrm{T}2}$ intervals chosen in this analysis, together with MC predictions from Pythia8, Herwig++ and Sherpa. The total uncertainty, including statistical and other experimental sources is also indicated using an error bar for the distributions and a green-shaded band for the ratios

Fig. 5

Non-perturbative correction factors for TEEC in the first and last bins of $H_{\mathrm{T}2}$ as a function of $cos\mathit{\varphi }$

Fig. 6

Ratios of the TEEC data in each $H_{\mathrm{T}2}$ bin to the NLO pQCD predictions obtained using the NNPDF 3.0 parton distribution functions, and corrected for non-perturbative effects

Fig. 7

Ratios of the ATEEC data in each $H_{\mathrm{T}2}$ bin to the NLO pQCD predictions obtained using the NNPDF 3.0 parton distribution functions, and corrected for non-perturbative effects

Fig. 8

Comparison of the TEEC data and the theoretical predictions after the fit. The value of ${\mathit{\alpha }}_{\mathrm{s}}(m_Z)$ used in this comparison is fitted independently for each energy bin

Fig. 9

Comparison of the values of ${\mathit{\alpha }}_{\mathrm{s}}(Q)$ obtained from fits to the TEEC functions at the energy scales given by $⟨H_{\mathrm{T}2}⟩/2$ (red star points) with the uncertainty band from the global fit (orange full band) and the 2016 world average (green hatched band). Determinations from other experiments are also shown as data points. The error bars, as well as the orange full band, include all experimental and theoretical sources of uncertainty. The strong coupling constant is assumed to run according to the two-loop solution of the RGE

Fig. 10

Comparison of the ATEEC data and the theoretical predictions after the fit. The value of ${\mathit{\alpha }}_{\mathrm{s}}(m_Z)$ used in this comparison is fitted independently for each energy bin

Fig. 11

Comparison of the values of ${\mathit{\alpha }}_{\mathrm{s}}(Q)$ obtained from fits to the ATEEC functions at the energy scales given by $⟨H_{\mathrm{T}2}⟩/2$ (red star points) with the uncertainty band from the global fit (orange full band) and the 2016 world average (green hatched band). Determinations from other experiments are also shown as data points. The error bars, as well as the orange full band, include all experimental and theoretical sources of uncertainty. The strong coupling constant is assumed to run according to the two-loop solution of the RGE