Subjet Multiplicity of Gluon and Quark Jets Reconstructed with the $k_{\perp}$ Algorithm in $p\bar{p}$ Collisions

TL;DR

This paper investigates the internal structure of gluon and quark jets in proton-antiproton collisions using the $k_{ot}$ algorithm, measuring subjet multiplicities and comparing them with theoretical predictions and previous experiments.

Contribution

First measurement of subjet multiplicities in gluon and quark jets reconstructed with the $k_{ot}$ algorithm in hadron collisions, providing insights into jet substructure and validating Monte Carlo models.

Findings

Measured the ratio of subjet multiplicities in gluon and quark jets as 1.84 ± 0.15 (stat.) ± 0.20 (sys).

Found that the $p_T$ of $k_{ot}$ jets exceeds cone jets by about 5-8 GeV at high $p_T$.

Results agree with HERWIG simulations and $e^+e^-$ data, close to the naive color charge ratio 2.25.

Abstract

The D0 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 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 R = 0.7, by about 5 (8) GeV at $p_T \approx 90$ (240) GeV. To examine internal jet structure, the $k_{\perp}$ algorithm is applied within D = 0.5 jets to resolve any subjets. The multiplicity of subjets in jet samples at $\sqrt{s} = 1800$ 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 $(M_{g} - 1) / (M_{q} - 1) = 1.84 \pm 0.15 (stat.) \pm ^{0.22}_{0.18} (sys.)$. 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 $C_A/C_F = 9/4 = 2.25$.