Non-perturbative effects in the energy-energy correlation

We consider the Energy-Energy Correlation function in electron-positron annihilation to hadrons. We concentrate on the back-to-back region, performing all-order resummation of the logarithmically enhanced contributions in QCD perturbation theory, up to next-to-next-to-next-to-leading logarithmic (N$^3$LL) accuracy. Away from the back-to-back region, we consistently combine resummed predictions with the known fixed-order results up to next-to-next-to-leading order (NNLO). All ...

We present the computation of energy-energy correlation in $e^+e^-$ collisions in the back-to-back region at next-to-next-to-leading logarithmic accuracy matched with the next-to-next-to-leading order perturbative prediction. We study the effect of the fixed higher order corrections in a comparison of our results to LEP and SLC data. The next-to-next-to-leading order correction has a sizable impact on the extracted value of $\alpha_{\mathrm S}(M_Z)$, hence its inclusion is ma...

We present the first fully analytic calculation of the Quantum Chromodynamics (QCD) event shape observable Energy-Energy Correlation in electron-positron annihilation at Next-To-Leading Order (NLO). This result sheds light on the analytic structure of the event shape observables beyond Leading Order (LO) and serves as a motivation to employ our methods in the investigation of other event shape observables that so far have not been calculated analytically.

The energy-energy correlation (EEC) between two detectors in $e^+e^-$ annihilation was computed analytically at leading order in QCD almost 40 years ago, and numerically at next-to-leading order (NLO) starting in the 1980s. We present the first analytical result for the EEC at NLO, which is remarkably simple, and facilitates analytical study of the perturbative structure of the EEC. We provide the expansion of EEC in the collinear and back-to-back regions through to next-to-l...

We consider $1/Q$ corrections to hard processes in QCD where Q is a large mass scale, concentrating on shape variables in $e^{+}e^{-}$ annihilation. While the evidence for such corrections can be and has been established by means of the renormalon technique, theory can be confronted with experiment only after clarifying the properties of the corresponding non-perturbative contribution. We list predictions based on the universality of the $1/Q$ terms, and compare them with the...

We investigate the power-suppressed corrections to the mean values of various quantities that characterise the shapes of final states in deep inelastic lepton scattering. Our method is based on an analysis of one-loop Feynman graphs containing a massive gluon, which is equivalent to the evaluation of leading infrared renormalon contributions. As in $\ee$ annihilation, we find that the leading corrections are proportional to $1/Q$. We give quantitative estimates based on the h...

Recent work on the theme of power corrections in perturbative QCD is briefly reviewed, with an emphasis on event shapes in e+ e- annihilation. The factorization of soft gluon effects is the main tool: it leads to resummation, and thus highlights the limitations of perturbation theory, pointing to nonperturbative corrections whose size can be estimated. Power corrections can be resummed into shape functions, for which QCD--based models are available. Theoretical progress is cl...

We consider the back-to-back region in the energy--energy correlation in e^+e^- collisions. We present the explicit expression of the O(as^2) logarithmically enhanced contributions up to next-to-next-to-leading logarithmic accuracy. We study the impact of the results in a detailed comparison with precise LEP and SLC data. We find that, when hadronization effects are taken into account as is customarily done in QCD analysis in e^+e^- annihilations, the extracted value of as(M_...

Power corrections to hadronic event shapes are estimated using a recently suggested relationship between perturbative and non-perturbative effects in QCD. The infrared cutoff dependence of perturbative calculations is related to non-perturbative contributions with the same dependence on the energy scale $Q$. Corrections proportional to $1/Q$ are predicted, in agreement with experiment. An empirical proportionality between the magnitudes of perturbative and non-perturbative co...

We consider power-behaved contributions to hard processes in QCD arising from non-perturbative effects at low scales which can be described by introducing the notion of an infrared-finite effective coupling. Our method is based on a dispersive treatment which embodies running coupling effects in all orders. The resulting power behaviour is consistent with expectations based on the operator product expansion, but our approach is more widely applicable. The dispersively-generat...