Study of prompt photon production in hadronic Z0 decays

Abreu, P. [--] Cortina Gil, Eduardo [UCL] DELPHI Collaboration [--] et al.

From a sample of 1.5 million Z ~ ---, qq decays collected by the DELPHI detector during 1991, 1992 and 1993, the production cross section for isolated final state photons is measured and is compared with the ~'(a, as) matrix element calculations implemented in the EEPRAD and GNJETS Monte Carlo generators. The observed photon yield is used to derive the electroweak couplings of charge 2/3 (u-type) and charge 1/3 (d-type) quarks to the Z ~ boson. The measured values C2/3 "- 0.91+_~ and cl/3 -- 1.62+~ are compatible with the Standard Model prediction, e2/3 ---- 1.145 and el~3 = 1.477.