Eur. Phys. J. C 21, 199-210 (2001)
DOI: 10.1007/s100520100742
A measurement of the QCD colour factors
using event shape distributions at
to 189 GeV
S. Kluth, P.A. Movilla Fernández, S. Bethke, C. Pahl and P. Pfeifenschneider Max-Planck-Institut für Physik, Werner-Heisenberg-Institut, Föhringer Ring 6, 80805 München, Germany
(Received: 3 May 2001 / Revised version: 2 June 2001 / Published online: 3 August 2001 -© Springer-Verlag / Società Italiana di Fisica 2001 )
Abstract
Measurements of the QCD colour factors CA and
CF and of the number
of active quark flavours nf in the process
at high
energy are presented. They
are based on fits of
+NLLA QCD
calculations to distributions of
the event shape observables 1-T, C,
BT and
BW measured at
centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects
are approximated with power correction calculations which also depend
on the QCD gauge structure. In this approach potential biases from
hadronisation models are reduced. Our results for individually
measured quantities obtained from 1-T and C
are
nf = 5.641.35,
CA = 2.880.27 and
CF = 1.450.27
in good agreement with QCD based on the SU(3) symmetry group where
nf=5 for the energies considered here,
CA=3 and
CF=4/3. From
simultaneous fits of CA and CF with
1-T and
C we find
CA = 2.840.24 and
CF = 1.290.18 ,
which is also in good agreement with the QCD expectation.
© Società Italiana di Fisica, Springer-Verlag 2001
