D. Buskulic et al., FIRST MEASUREMENT OF THE QUARK-TO-PHOTON FRAGMENTATION FUNCTION, Zeitschrift fur Physik. C, Particles and fields, 69(3), 1996, pp. 365-377
Earlier measurements at LEP of isolated hard photons in hadronic Z dec
ays, attributed to radiation from primary quark pairs, have been exten
ded in the ALEPH experiment to include hard photon production inside h
adron jets. Events are selected where all particles combine democratic
ally to form hadron jets, one of which contains a photon with a fracti
onal energy z greater than or equal to 0.7. After statistical subtract
ion of non-prompt photons, the quark-to-photon fragmentation function,
D(z), is extracted directly from the measured 2-jet rate. By taking i
nto account the perturbative contributions to D(z) obtained from an O(
alpha alpha(s)) QCD calculation, the unknown non-perturbative componen
t of D(z) is then determined at high z. Provided due account is taken
of hadronization effects near z = 1, a good description of the other e
vent topologies is then found.