P. Abreu et al., MEASUREMENT OF THE TRIPLE-GLUON VERTEX FROM 4-JET EVENTS AT LEP, Zeitschrift fur Physik. C, Particles and fields, 59(3), 1993, pp. 357-368
From the combined data of 1990 and 1991 of the DELPHI experiment at LE
P, 13057 4-jet events are obtained and used for determining the contri
bution of the triple-gluon vertex. The relevant variables are the gene
ralized Nachtmann Reiter angle theta(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+/-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-g
luon 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.