Subjet multiplicity of gluon and quark jets reconstructed with the $k_{\perp }$ algorithm in $p\overline{p}$ collisions

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 ${(k}_{\perp })$ of energy clusters. Using the standard value $D=1.0\mathrm{}$ of the jet-separation parameter in the $k_{\perp }$ algorithm, we find that the $p_T$ of such jets is higher than the $E_T$ of matched jets reconstructed with cones of radius $\mathcal{R}=0.7,$ by about 5 (8) GeV at $p_T\approx 90\hspace{0.5em}\mathrm{}\left(240\right)\mathrm{}\hspace{0.5em}\mathrm{GeV}.$ To examine internal jet structure, the $k_{\perp }$ algorithm is applied within $D=0.5\mathrm{}$ jets to resolve any subjets. The multiplicity of subjets in jet samples at $\sqrt{s}=1800\mathrm{}\hspace{0.5em}\mathrm{GeV}$ 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 $\left(〈M_g〉-1\right)/\left(〈M_q〉-1\right)=1.84\pm 0.15\hspace{0.5em}\left(\mathrm{stat}\right){\pm }_{0.18}^{0.22}\hspace{0.5em}\left(\mathrm{syst}\right).\mathrm{}$ 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 $C_A{/C}_F=9/4=\mathrm{2.25.}\mathrm{}$