Test of Colour Reconnection Models using Three-Jet Events in Hadronic Z Decays

TL;DR

This study tests different colour reconnection models in three-jet hadronic Z decays, finding that certain string-based models with specific parameters align better with experimental data, thus constraining CR model parameters.

Contribution

It provides the first detailed comparison of string-based colour reconnection models with three-jet Z decay data, constraining model parameters based on observed particle distributions.

Findings

CR models predict too high rates, disfavoured by data

Standard non-CR models predict too low rates

GAL model with small R_0 fits the data well

Abstract

Hadronic Z decays into three jets are used to test QCD models of colour reconnection (CR). A sensitive quantity is the rate of gluon jets with a gap in the particle rapidity distribution and zero jet charge. Gluon jets are identified by either energy-ordering or by tagging two b-jets. The rates predicted by two string-based tunable CR models, one implemented in JETSET (the GAL model), the other in ARIADNE, are too high and disfavoured by the data, whereas the rates from the corresponding non-CR standard versions of these generators are too low. The data can be described by the GAL model assuming a small value for the R_0 parameter in the range 0.01-0.02.