Determination of the e+e- -> gamma gamma (gamma) cross-section at centre-of-mass energies ranging from 189 GeV to 202 GeV

A test of the QED process e(+)e(-) --> gamma gamma>(*) over bar *(gamma) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb(-1). The differential and total cross-sections for the process e(+)e(-) --> gamma gamma were measured, and found to be in agreement with the QED prediction. 95% confidence level (C.L.) lower limits on the QED cut-off parameters of Lambda (+) > 330 GeV and Lambda_ > 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c(2) (for lambda gamma = 1) was obtained, s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M-S: M-S > 713 GeV/c(2) (lambda = 1) and M-S > 691 GeV/c(2) (lambda = -1). (C) 2000 Published by Elsevier Science B.V.