Measurement of the triple-gluon vertex from 4-jet events at LEP (original) (raw)

1993, Zeitschrift f�r Physik C Particles and Fields

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 v ariables are the generalized Nachtmann Reiter angle NR and the opening angle of the two least energetic jets. A t to their two-dimensional distribution yields C A =C F = 2 : 12 0:35 and N C =N A = 0 : 46 0:19 where C A =C F is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, and N 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 to C A =C F. The results are in agreement with the values expected from QCD: C A =C F = 2:25, and N C =N A = 3 = 8.