Date: Wednesday 28th March 2001
Title: The LEP Energy Spectrometer
Speaker: Dr. John Matheson (Rutherford Lab.)
Abstract
At LEP I, measurement of the beam energy was performed with high
accuracy by
resonant depolarisation. At physics energies for LEP II, polarisation
of the beams is not achievable and measurements of the total bending
field
are used, calibrated against resonant depolarisation over the range
41-60 GeV/beam. Uncertainties arise from regions of the field which
are
not sampled adequately.
The LEP Spectrometer was proposed to give a determination of beam
energy for
LEP II. The instrument consists of a steel dipole flanked by beam
position
monitors (BPMs) which allow measurement of changes in the bend angle.
The aim is to achieve a relative precision of 1x10-4 on the energy,
which
requires knowledge of the integral magnetic field to 3x10-5
and 1 micron
resolution from the BPMs.
The Spectrometer was first comissioned during the 1999 LEP running
period.
The talk will outline energy measurement at LEP, the Spectrometer
hardware and the characterisation of the individual subsystems. The
current status of the data analysis will be reviewed.