Tests of Power Corrections for Event Shapes in e+e- Annihilation

TL;DR

The paper tests the Dokshitzer-Marchesini-Webber power-correction framework for hadronisation in e+e- annihilation by fitting perturbative QCD predictions (O(alpha_s^2) + NLLA) with analytic power corrections to both differential event-shape distributions and their means across 14–189 GeV. It performs simultaneous fits to extract alpha_s(MZ) and the non-perturbative parameter alpha0(2GeV), examining universality of alpha0 and the impact of hadronisation on precision QCD tests. The study finds overall good agreement between data and theory, with final combined results alpha_s(MZ) = 0.1171^{+0.0032}_{-0.0020} and alpha0(2GeV) = 0.513^{+0.066}_{-0.045}, supporting universality within uncertainties, though some observables (notably B_W) show tensions that may indicate residual higher-order effects. These results reinforce the viability of analytic power corrections for describing hadronisation in event shapes and provide competitive determinations of the strong coupling and non-perturbative parameters across a broad energy range.

Abstract

A study of perturbative QCD calculations combined with power corrections to model hadronisation effects is presented. The QCD predictions are fitted to differential distributions and mean values of event shape observables measured in e+e- annihilation at centre-of-mass energies from 14 to 189 GeV. We investigate the event shape observables thrust, heavy jet mass, C-parameter, total and wide jet broadening and differential 2-jet rate and observe a good description of the data by the QCD predictions. The strong coupling constant alpha_S(M_Z) and the free parameter of the power correction calculations alpha_0(2 GeV) are measured to be alpha_S(M_Z) = 0.1171 +/- 0.0032/0.0020 and alpha_0(2 GeV) = 0.513 +/- 0.066/0.045. The predicted universality of alpha_0 is confirmed within the uncertainties of the measurements.

Figures (8)

• Figure 1: The figure presents hadronisation correction factors at $\sqrt{s}=35$ GeV estimated using power corrections (solid lines) or using the JETSET Monte Carlo program (dashed lines). The hadronisation corrections for power corrections are given by the ratio of the perturbative QCD prediction over the same prediction combined with power corrections using the fitted values of $\alpha_{\mathrm{S}}(M_{\mathrm{Z^0}})$ and $\alpha_{\mathrm{0}}({\mathrm{2~GeV}})$. The Monte Carlo hadronisation corrections are given by the ratio of distributions calculated at the parton- and hadron-level, respectively.
• Figure 2: The figure presents ratios of distributions of $1-T$ calculated using u, d, s, and c quarks events or all events using Monte Carlo simulation. The different line types indicate the cms energy at which the Monte Carlo simulation was run.
• Figure 3: Scaled distributions for $1-T$ measured at $\sqrt{s}=14$ to 189 GeV. The error bars indicate the total errors of the data points. The solid lines show the result of the simultaneous fit of $\alpha_{\mathrm{S}}(M_{\mathrm{Z^0}})$ and $\alpha_{\mathrm{0}}$ using resummed $\mathcal{O}(\alpha_{\mathrm{S}}^2)$+NLLA QCD predictions with the ln(R)-matching combined with power corrections. The dotted lines represent an extrapolation of the fit result.
• Figure 4: Scaled distributions for $M_{\mathrm{H}}$ and $M_{\mathrm{H}}^2$ measured at $\sqrt{s}=14$ to 189 GeV. The error bars indicate the total errors of the data points. The solid lines show the result of the simultaneous fit of $\alpha_{\mathrm{S}}(M_{\mathrm{Z^0}})$ and $\alpha_{\mathrm{0}}$ using resummed $\mathcal{O}(\alpha_{\mathrm{S}}^2)$+NLLA QCD predictions with the ln(R)-matching combined with power corrections. The dotted lines represent an extrapolation of the fit result.
• Figure 5: Scaled distributions for $B_{\mathrm{T}}$ and $B_{\mathrm{W}}$ measured at $\sqrt{s}=35$ to 189 GeV. The error bars indicate the total errors of the data points. The solid lines show the result of the simultaneous fit of $\alpha_{\mathrm{S}}(M_{\mathrm{Z^0}})$ and $\alpha_{\mathrm{0}}$ using resummed $\mathcal{O}(\alpha_{\mathrm{S}}^2)$+NLLA QCD predictions with the ln(R)-matching combined with power corrections. The dotted lines represent an extrapolation of the fit result.