The total and the differential cross sections for the reaction e+e- --> gammagamma(gamma) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb-1. The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are LAMBDA+ > 143 GeV and LAMBDA- > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant lambda(gamma) = 1 is 132 GeV/c2. Upper limits on the branching ratios for the decays Z0 --> gammagamma, Z0 --> pi0gamma, Z0 --> etagamma and Z0 --> gammagammagamma have been determined to be 5.5 x 10(-5), 5.5 x 10(-5), 8.0 x 10(-5), and 1.7 x 10-5 respectively. All the limits are at the 95% confidence level.
Measurement of the e+e- -] gamma-gamma(gamma) cross-section at LEP energies
CACCIA, MASSIMO;PREST, MICHELA;
1994-01-01
Abstract
The total and the differential cross sections for the reaction e+e- --> gammagamma(gamma) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb-1. The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are LAMBDA+ > 143 GeV and LAMBDA- > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant lambda(gamma) = 1 is 132 GeV/c2. Upper limits on the branching ratios for the decays Z0 --> gammagamma, Z0 --> pi0gamma, Z0 --> etagamma and Z0 --> gammagammagamma have been determined to be 5.5 x 10(-5), 5.5 x 10(-5), 8.0 x 10(-5), and 1.7 x 10-5 respectively. All the limits are at the 95% confidence level.
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