QCD Analysis of Unpolarized and Polarized Lambda - Baryon Production in Leading and Next-to-Leading Order

TL;DR

The paper addresses the challenge of describing Lambda baryon production in e+e- and SIDIS within perturbative QCD by employing scale-dependent, time-like fragmentation functions. It develops a complete NLO framework for the evolution of these fragmentation functions, fits unpolarized D_f^Λ from extensive SIA data at a low starting scale, and proposes three polarized ΔD_f^Λ scenarios guided by LEP measurements. The work finds that unpolarized Λ fragmentation functions describe existing SIDIS data reasonably well, while the polarized sector remains poorly constrained, with scenario-dependent predictions for spin-transfer observables. It demonstrates that future SIDIS measurements at facilities like HERA and HERMES can discriminate among polarized fragmentation-function scenarios, thereby guiding experimental efforts to pin down the spin structure of Lambda fragmentation and the role of unfavoured and gluon contributions.

Abstract

We analyze experimental data for the production of Lambda baryons in e^+e^- annihilation in terms of scale dependent, QCD evolved, Lambda fragmentation functions. Apart from the vast majority of the data for which the polarization of an observed Lambda was not determined, we also consider the recent LEP measurements of the longitudinal polarization of Lambda's produced on the Z-resonance. Such data correspond to spin-dependent fragmentation functions for the Lambda. We point out that the present data are insufficient to satisfactorily fix these. We therefore suggest several different sets of fragmentation functions, all compatible with present data, and study the prospects for conceivable future semi-inclusive deep-inelastic scattering experiments to discriminate between them. We provide the complete next-to-leading order QCD framework for all the processes we consider.