ENERGY-DEPENDENCE OF RATIOS OF MULTIPLICITIES AND THEIR SLOPES FOR GLUON AND QUARK JETS

The difference between the ratio of multiplicities and the ratio of th eir derivatives with respect to energy for gluon and quark jets is cal culated up to next-to-next-to leading order of perturbative QCD. Its n onzero value is uniquely defined by the running property of the QCD co upling constant. It is shown that this difference is rather small comp ared to values which can be obtained from experimental data. This disa greement can be ascribed either to strong nonperturbative terms or to experimental problems with a scale choice, jet separation, and inadequ ate assignment of soft particles to jets. (C) 1998 American Institute of Physics. [S0021-3640(98)00219-9].