Absolute calibration of electromagnetic calorimeter at LHC with physics processes

Physics processes Z/sup 0/ to e/sup +/e/sup -/, W to e/sup +or-/ nu /sub e/, J/ psi to e/sup +/e/sup -/ and Upsilon (1s) to e/sup +/e/sup -/ were investigated for calibration of the electromagnetic calorimeter in site at LHC. The production cross sections of these processes, including high order corrections, were calculated by using PYTHIA 6.136 as well as CDF data. As an example, the Level 1 trigger efficiency was calculated by using events simulated with CMSIM 121 and ORCA_4_4_0_optimized. The result of this investigation indicates that although the process of J/ psi to e/sup +/e/sup -/ has a factor of 16,000 larger cross section as compared to that of Z/sup 0/ to e /sup +/e/sup -/, about 1 or 0.5 year data taking at relatively low luminosity of 10/sup 32/ cm/sup -2/s/sup -1/ or 10/sup 33/ cm/sup -2 /s/sup -1/ respectively is still required to reach a subpercent calibration precision by using electron pairs from J/ psi . A combination of all physics processes thus may be needed at the beginning of the data taking. (12 refs).