A Monte Carlo study of the quark- and gluon-jets of different hardness in three-jet events identified by b-tag method

摘要

Quark- and gluon-jets are compared in three-jet events generated by Jetset 7.4 and Herwig 5.9 at roots = 91.2 GeV. Jets are obtained using the Durham algorithm. The quark jets are identified by b-tag tracing, the remaining jet is then defined as a gluon jet. The average values of transverse momentum (t)> and multiplicity versus hardness as well as the jet-mean transverse momentum and multiplicity (p) over bar (t) -N correlation in quark- and gluon-jets of different hardness are compared. It turns out that the (t)> and of quark jets are insensitive to hardness, while those of the gluon jets change abruptly with hardness. When hardness is high, H-d > 10 GeV, the (t)> and of gluon jets are larger than those of quark jets; but when hardness is low, H-d < 10 GeV, the result is opposite. On the other hand, the (p) over bar (t) and N are uncorrelated in gluon jets when H (d) > 10 GeV, but are negatively correlated when H-d < 10 GeV. The relation between the scale H-d = 10 GeV obtained in this way and the scale for 'circular' jets found earlier in the dynamical-fluctuation analysis is discussed.