Excerpt of an E-mail sent by Ilias Eftymiopoulos, in charge of the SPS North Area (and in particular of H4) to Benoit (02/15/08):
******************************************************************************************************************************************************************************************************************************
Benoit,
The absolute energy of the beam line depends on our geometry and absolute knowledge of the current in the power supplies. It was measured long time ago (NA8 experiment if I remember well) and found to be about 0.3%. Last year NA61 did a measurement looking the tacks of the beam particles in their spectrometer and found the same value.
The beam resolution is max +-1.5% (acceptance in delta-p) which is small compared to the resolution of your calorimeter.
I am not sure how CMS-ECAL could help you with your questions. They have been using different beam files, or at least we should check before that you refer to the same files before attempting any comparison.
Regards,
Ilias Efthymiopoulos
CERN/AB Department
*******************************************************************************************************************************************************************************************************************************