DOI 10.1007/s100529900137
Evaluation of the LEP centre-of-mass energy above the W-pair production threshold
The LEP Energy Working Group
A. Blondel1 -
M. B
ge2 -
E. Bravin2 -
P. Bright-Thomas2 -
T. Camporesi2 -
B. Dehning2 -
M. Heemskerk2 -
M. Hildreth2 -
M. Koratzinos2 -
E. Lançon3 -
G. Mugnai2 -
A. Müller2,4 -
E. Peschardt2 -
M. Placidi2 -
N. Qi2 -
G. Quast4 -
P. Renton5 -
F. Sonnemann2 -
E. Torrence2 -
A. Weber6 -
P.S. Wells2 -
J. Wenninger2 -
G. Wilkinson2
1 Laboratoire de Physique Nucléaire et des Hautes Energies,
Ecole Polytechnique, IN2P3-CNRS, 91128 Palaiseau Cedex,
France
2 CERN, European Organisation for Particle Physics,
1211 Geneva 23, Switzerland
3 CEA, DAPNIA/Service de Physique des Particules, CEA-Saclay,
91191 Gif-sur-Yvette Cedex, France
4 Institut für Physik, Universität Mainz, 55099
Mainz,
Germany
5 Department of Physics, University of Oxford, Keble Road,
Oxford
OX1 3RH, UK
6 Aachen I (RWTH), I. Physikalisches Institut,
Sommerfeldstrasse, Turm 28, 52056 Aachen, Germany
Received: 14 December 1998 / Published online: 3 November 1999
Abstract
Knowledge of the centre-of-mass energy at LEP2
is of primary importance to set the absolute energy scale
for the measurement of the W-boson mass.
The beam energy above 80GeV is derived from continuous
measurements of the magnetic bending field by
16 NMR probes situated in a number of the LEP dipoles.
The relationship between the fields measured
by the probes and the
beam energy is calibrated against
precise measurements of the average
beam energy between 41 and 55GeV made using
the resonant depolarisation technique.
The linearity of the relationship is tested by
comparing the fields measured by the probes with the
total bending field measured by a flux loop.
This test results in the largest contribution to the systematic
uncertainty.
Several further corrections are applied to derive
the centre-of-mass energies
at each interaction point.
In addition, the centre-of-mass energy spread is evaluated.
The beam energy
has been determined
with a precision of 25MeV for the data taken in 1997,
corresponding to a relative precision of
.
This is small in comparison to the present uncertainty
on the W mass measurement at LEP. However, the ultimate
statistical precision on the W mass with the full LEP2 data sample
should be around 25MeV, and a smaller uncertainty
on the beam energy is desirable. Prospects for
improvements are outlined.
Copyright Springer-Verlag
