Author/Authors :
NA49 Collaboration، نويسنده , , S.V. Afanasiev، نويسنده , , T. Anticic، نويسنده , , J. Bachler، نويسنده , , D. Barna، نويسنده , , L.S. Barnby، نويسنده , , J. Bartke، نويسنده , , R.A. Barton، نويسنده , , L. Betev، نويسنده , , H. Bia?kowska، نويسنده , , A. Billmeier، نويسنده , , C. Blume، نويسنده , , C.O. Blyth، نويسنده , , B. Boimska، نويسنده , , J. Bracinik، نويسنده , , F.P. Brady، نويسنده , , R. Brun، نويسنده , , P. Bun?i?، نويسنده , , L. Carr، نويسنده , , D. Cebra، نويسنده , , et al.، نويسنده ,
Abstract :
A test of the QED process e+e−→γγ(γ) 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−→γγ 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 Λ+>330 GeV and Λ−>320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c2 (for λγ=1) was obtained. s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, MS: MS>713 GeV/c2 (λ=1) and MS>691 GeV/c2 (λ=−1).
