A Monte Carlo Study on Cone-Angle Property of the Quark- and Gluon-Jets Identified by b-Tag Method

Quark and gluon jets are studied in three-jet events generated by Jetset 7.4 and Herwig 5.9 at √s = 91.2GeV. The quark jets are identified by b-tag tracing, and the remaining jet is then defined as the gluon jet. A new physical variable, i.e. the cone-angle, which is able to describe the geometrical characteristic of the jet, is defined. It turns out that the cone-angle distribution of the gluon jet is wider than its mother quark jet, i.e. the gluon jet is ``fatter''. As the multiplicity increases, the cone-angle distribution of the quark jet has an upward-going trend, i.e. a positive correlation is present. The cone-angle of the gluon and quark jet versus their transverse momentum develop a valley. The mean cone-angles of both the gluon jet and the quark jet are negatively correlated with the transverse momentum for p_t < 3GeV/c, but are positively correlated for p_t > 3GeV/c. The mean cone-angles of the gluon and quark jets are well separated, showing that they can be utilized in the identification of the two kinds of jets.