Determination of the QCD color factor ratio CA/CF from the scale dependence of multiplicity in three jet events

TL;DR

This paper investigates the QCD color factor ratio CA/CF through the energy dependence of particle multiplicity in three jet events, demonstrating a method that aligns with theoretical expectations and applying it to experimental data.

Contribution

It introduces a one-parameter fitting method for CA/CF that accounts for energy conservation, providing a more accurate determination from experimental data.

Findings

The one-parameter fit yields CA/CF=2.25 at high energies in simulations.

Applying the method to DELPHI data gives CA/CF=1.74±0.03±0.10 at the Z0 energy.

Two-parameter fits do not recover the expected CA/CF value in the asymptotic limit.

Abstract

I examine the determination of the QCD color factor ratio CA/CF from the scale evolution of particle multiplicity in e+e- three jet events. I fit an analytic expression for the multiplicity in three jet events to event samples generated with QCD multihadronic event generators. I demonstrate that a one parameter fit of CA/CF yields the expected result CA/CF=2.25 in the limit of asymptotically large energies if energy conservation is included in the calculation. In contrast, a two parameter fit of CA/CF and a constant offset to the gluon jet multiplicity, proposed in a recent study, does not yield CA/CF=2.25 in this limit. I apply the one parameter fit method to recently published data of the DELPHI experiment at LEP and determine the effective value of CA/CF from this technique, at the finite energy of the Z0 boson, to be 1.74+-0.03+-0.10, where the first uncertainty is statistical and the second is systematic.