Evidence for final state photons in multihadronic decays of the Z0

Abstract From the observed yield and properties of isolated energetic photons in the reaction e + e − →Z 0 →hadrons+ γ measured with the OPAL detector at LEP, evidence for final state radiation from primary quarks is obtained. Combined with the measurement of the total hadronic width of the Z 0 , the observed rate allows the extraction of the electroweak coupling constants of up and down type quarks: ν 1 3 2 + a 1 3 2 = 1.24±0.47 and ν 2 3 2 + a 2 3 2 = 1.72±0.70 No evidence for additional photon production from anomalous decays of the Z 0 or from decays of new particles is found. This measurement limits the contribution to the total Z 0 width from such sources to be less than 8.2 MeV at the 95% confidence level.