Subjet multiplicity of gluon and quark jets reconstructed with thek⊥algorithm inpp¯collisions

The D empty set Collaboration has studied for the first time the properties of hadron-collider jets reconstructed with a successive-combination algorithm based on relative transverse momenta (k(perpendicular to)) of energy clusters. Using the standard value D = 1.0 of the jet-separation parameter in the k(perpendicular to) algorithm, we find that the p(T) of such jets is higher than the E-T of matched jets reconstructed with cones of radius R = 0.7, by about 5 (8) GeV at p(T) approximate to90 (240) GeV. To examine internal jet structure, the k(perpendicular to) algorithm is applied within D = 0.5 jets to resolve any subjets. The multiplicity of subjets in jet samples at roots = 1800 GeV and 630 GeV is extracted separately for gluons (M (g) ) and quarks (M q), and the ratio of average subjet multiplicities in gluon and quark jets is measured as ([M g] - 1)/([M q] - 1) = 1.84+/-0.15 (stat)(-0.18)(+0.22) (syst). This ratio is in agreement with the expectations from the HERWIG Monte Carlo event generator and a resummation calculation, and with observations in e(+) e(-) annihilations, and is close to the naive prediction for the ratio of color charges of C-A/C-F = 9/4 = 2.25.