Date: Wednesday 28th March 2001
Title: The LEP Energy Spectrometer
Speaker: Dr. John Matheson (Rutherford Lab.)
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.