DOI 10.1007/s100529900034
Four jet event shapes in electron-positron annihilation
J.M. Campbell - M.A. Cullen - E.W.N. Glover
Department of Physics, University of Durham, Durham DH1 3LE, UK
Received: 17 November 1998 / Revised version: 26 January 1999 / Published online: 7 April 1999
Abstract
We report next-to-leading order perturbative QCD predictions of 4 jet event
shape variables for the process 
obtained using the
general purpose Monte Carlo EERAD2. This program is based on the known
`squared' one loop matrix elements for the virtual 
parton
contribution and squared matrix elements for 5 parton production. To combine
the two distinct final states numerically we present a hybrid of the commonly
used subtraction and slicing schemes based on the colour antenna structure of
the final state which can be readily applied to other processes. We have
checked that the numerical results obtained with EERAD2 are consistent
with next-to-leading order estimates of the distributions of previously
determined four jet-like event variables. We also report the next-to-leading
order scale independent coefficients for some previously uncalculated
observables; the light hemisphere mass, narrow jet broadening and
the 4 jet transition variables with respect to the JADE and Geneva jet finding
algorithms. For each of these observables, the next-to-leading order
corrections calculated at the physical scale significantly increase the rate
compared to leading order (the K factor is approximately 1.5 - 2). With the
exception of the 4 jet transition variables, the published DELPHI data lies
well above the 
predictions. The renormalisation scale
uncertainty is still large and in most cases the data prefers a scale
significantly smaller than the physical scale. This situation is reminiscent of
that for three jet shape variables, and should be improved by the inclusion of
power corrections and resummation of large infrared logarithms.
Copyright Springer-Verlag
