Production of K^0_S and Lambda in Quark and Gluon Jets from Z^0 Decay

TL;DR

This study measures the production rates of K^0_S mesons and Lambda baryons in quark and gluon jets from Z^0 decay using two methods, providing insights into jet composition and particle production mechanisms.

Contribution

It introduces a new collimation-based method for identifying quark jets and compares production rates in quark and gluon jets using two different techniques.

Findings

Gluon jets have higher Lambda production rates than quark jets.

K^0_S production ratios are close to unity in different jet types.

Results are consistent with Monte Carlo model predictions.

Abstract

The production of K^0_S mesons and Lambda baryons in quark and gluon jets has been investigated using two complementary techniques. In the first approach, which provides high statistical accuracy, jets were selected using different jet finding algorithms and ordered according to their energy. Production rates were determined taking into account the dependences of quark and gluon compositions as a function of jet energy as predicted by Monte Carlo models. Selecting three-jet events with the k_perp (Durham) jet finder (y_cut = 0.005), the ratios of K^0_S and Lambda production rates in gluon and quark jets relative to the mean charged particle multiplicity were found to be 1.10 +/- 0.02 +/- 0.02 and 1.41 +/- 0.04 +/- 0.04, respectively, where the first uncertainty is statistical and the second is systematic. In the second approach, a new method of identifying quark jets based on the collimation of energy flow around the jet axis is introduced and was used to anti-tag gluon jets in symmetric (Y-shaped) three-jet events. Using the cone jet finding algorithm with a cone size of 30 degrees, the ratios of relative production rates in gluon and quark jets were determined to be 0.94 +/- 0.07 +/- 0.07 for K^0_S and 1.18 +/- 0.10 +/- 0.17 for Lambda. The results of both analyses are compared to the predictions of Monte Carlo models.