Four-jet angular distributions and color charge measurements: Leading order versus next-to-leading order

Abstract

We present the next-to-leading order perturbative QCD prediction to the four-jet angular distributions used by experimental collaborations at CERN LEP for measuring the QCD color charge factors. We compare our results to ALEPH data corrected to the parton level. We perform a leading order ''measurement'' of the QCD color factor ratios by fitting the leading order perturbative predictions to the next-to-leading order result. Our result shows that in an experimental analysis for measuring the color charge factors the use of the O(␣ s 3 ) QCD predictions instead of the O(␣ s 2 ) results may shift the center of the fit by a relative factor of 1ϩ2␣ s in the

A simultaneous measurement of the QCD colour factors and the strong coupling

“…Our resolution criterion of y cut = 0.008 is safely larger than the intrinsic cut-off. For normalised angular correlations, the distributions at leading and next-to-leading order are almost the same [14,19]. Thus for the purpose of determining the corrections the ERT Monte Carlo events are sufficient.…”

“…For multi-jet rates as well as numerous event shape distributions with perturbative expansions starting at O(α s ), matched next-to-leading order and nextto-leading logarithmic approximations provide very precise descriptions of the data over a wide range of the available kinematic region [15][16][17][18]. Also, recently, the next-to-leading order predictions for the distributions of four-jet angular correlations have been calculated [14,19]. To make use of these developments, we perform a simultaneous fit of the strong coupling and ratios of colour factors using next-to-leading order predictions of four-jet rates, differential two-jet rates and four-jet angular correlations.…”

“…On the one hand, even the normalised next-to-leading order predictions for the angular distributions depend upon α s [14], while on the other hand, α s itself depends on the colour factors through its running. In this sense, beyond leading order, the only consistent way to determine the three free parameters is a simultaneous measurement of the strong coupling and the colour factors.…”

“…In fact, in Ref. [14] the value of T R /C F (see the Appendix) was estimated to increase about 25% if next-to-leading order (NLO) theoretical predictions are used instead of the leading order (LO) ones. It is therefore desirable to explicitly verify the effect of the next-to-leading order corrections on these normalised angular distributions.…”

Six-quark decays of off-shell $W^+W^-$ pairs via parton-level QCD in electron-positron annihilations

“…These have comparable production rates, which is a most welcome result. After all, the smallness of the SUSY effect with respect to ordinary QCD dynamics was really the limiting factor of the experimental analyses performed at LEP1, given that even the very large next-to-leading-order (NLO) corrections to the four-jet sample leave the shape of the distributions used to fit C A , C F and T F practically unaltered [23]. For all the above reasons, we believe it then important looking into this aspect of six-jet phenomenology.…”