Subjet multiplicity of gluon and quark jets reconstructed with the k⊥ algorithm in pp̅ collisions

Abstract

The DØ 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⊥) of energy clusters. Using the standard value D=1.0 of the jet-separation parameter in the k⊥ 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≈90 (240) GeV. To examine internal jet structure, the k⊥ algorithm is applied within D=0.5 jets to resolve any subjets. The multiplicity of subjets in jet samples at √s=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.