On the OPAL 'string effect' and quark-gluon jet differences in three-jet symmetric events

The OPAL collaboration has recently presented data on e++e-→hadrons at LEP with 3 jets in the final state in configurations symmetric with respect to the directions of the two secondary jets, one of which is lepton-tagged as a quark jet. The data show the presence of an asymmetry in the population of particles in the regions between jets, commonly called the string effect, and of quark-gluon jet differences. We show that the observed effects can be accounted for by an independent jet fragmentation model, in which quark and gluon jets have different fragmentation properties and in which phase-space effects associated with jet invariant masses are taken into account. There is not need to include parton coherence effects. (orig.)