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Measurement of the triple-gluon vertex from 4-jet events at LEP

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Zeitschrift für Physik C Particles and Fields

Abstract

From the combined data of 1990 and 1991 of the DELPHI experiment at LEP, 13057 4-jet events are obtained and used for determining the contribution of the triple-gluon vertex. The relevant variables are the generalized Nachtmann Reiter angle θ * NR and the opening angle of the two least energetic jets. A fit to their two-dimensional distribution yields

$$C_A /C_F = 2.12 \pm 0.35 and N_C /N_A = 0.46 \pm 0.19,$$

whereC A/C F is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, andN C/N A, the ratio of the number of quark colours to the number of gluons.

This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional toC A/C F. The results are in agreement with the values expected from QCD:C A/C F=2.25, andN C/N A=3/8.

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DELPHI Collaboration., Abreu, P., Adam, W. et al. Measurement of the triple-gluon vertex from 4-jet events at LEP. Z. Phys. C - Particles and Fields 59, 357–368 (1993). https://doi.org/10.1007/BF01498617

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