Average gluon and quark jet multiplicities

TL;DR

This paper advances the calculation of average gluon and quark jet multiplicities in QCD by incorporating recent small-x resummation techniques, leading to precise parameter fits and an alpha_s value consistent with the world average.

Contribution

It introduces new QCD calculations for jet multiplicities using small-x resummation in the MSbar scheme, with a global fit to experimental data.

Findings

Determined alpha_s(Mz)=0.1199 ± 0.0026, consistent with the world average.

Resolved a longstanding problem in QCD related to jet multiplicity predictions.

Achieved a theoretical precision equivalent to NNLL resummation plus NNLO effects.

Abstract

We show the results in [1,2] for computing the QCD contributions to the scale evolution of average gluon and quark jet multiplicities. The new results came due a recent progress in timelike small-x resummation obtained in the MSbar factorization scheme. They depend on two nonperturbative parameters with clear and simple physical interpretations. A global fit of these two quantities to all available experimental data sets demonstrates by its goodness how our results solve a longstandig problem of QCD. Including all the available theoretical input within our approach, alphas(Mz)=0.1199 +- 0.0026 has been obtained in the MSbar scheme in an approximation equivalent to next-to-next-to-leading order enhanced by the resummations of ln x terms through the NNLL level and of ln Q2 terms by the renormalization group. This result is in excellent agreement with the present world average.