Subjet Multiplicity in Quark and Gluon Jets at D0

TL;DR

This paper measures the subjet multiplicity in quark and gluon jets at different energies to understand their differences, using data from the D0 experiment and Monte Carlo simulations.

Contribution

It provides the first measurement of subjet multiplicities for quark and gluon jets at Tevatron energies, including the ratio of their multiplicities.

Findings

Gluon jets have higher subjet multiplicity than quark jets.

The measured ratio R is approximately 1.91, indicating more substructure in gluon jets.

Monte Carlo predictions align with the measured multiplicities.

Abstract

We measure the subjet multiplicity M in jets reconstructed with a successive combination type of jet algorithm (k_T). We select jets with 55<E_T<100 GeV and | \eta | < 0.5. We compare similar samples of jets at sqrt{s} = 1800 and 630 GeV. The HERWIG Monte Carlo simulation predicts that 59% of the jets are gluon jets at \sqrt{s} = 1800, and 33% at sqrt{s} = 630. Using this information, we extract the subjet multiplicity in quark (M_q) and gluon (M_g) jets. We also measure the ratio $R\equiv \frac{\left< M_{q}\right> -1}{% \left< M_{g}\right> -1}= 1.91 \pm 0.04{\rm(stat)} ^{+0.23}_{-0.19} {\rm(sys)}$.