Abstract
We present NNFF1.0, a new determination of the fragmentation functions (FFs) of charged pions, charged kaons, and protons/antiprotons from an analysis of single-inclusive hadron production data in electron–positron annihilation. This determination, performed at leading, next-to-leading, and next-to-next-to-leading order in perturbative QCD, is based on the NNPDF methodology, a fitting framework designed to provide a statistically sound representation of FF uncertainties and to minimise any procedural bias. We discuss novel aspects of the methodology used in this analysis, namely an optimised parametrisation of FFs and a more efficient chi ^2 minimisation strategy, and validate the FF fitting procedure by means of closure tests. We then present the NNFF1.0 sets, and discuss their fit quality, their perturbative convergence, and their stability upon variations of the kinematic cuts and the fitted dataset. We find that the systematic inclusion of higher-order QCD corrections significantly improves the description of the data, especially in the small-z region. We compare the NNFF1.0 sets to other recent sets of FFs, finding in general a reasonable agreement, but also important differences. Together with existing sets of unpolarised and polarised parton distribution functions (PDFs), FFs and PDFs are now available from a common fitting framework for the first time.
Highlights
The knowledge of fragmentation functions (FFs) is an important ingredient in our understanding of non-perturbative QCD dynamics, as well as an essential tool in the description of a number of processes used to examine the internal structure of nucleons
Theoretical investigations of the effect of next-to-next-to-leading order (NNLO) QCD corrections [24], of a general treatment of heavy-quark mass effects [25], and of all-order small-z resummation [26] were performed in the framework of the DEHSS analyses, only for the Single-Inclusive Annihilation (SIA) production of charged pions
As expected, the χ 2/Ndat is close to zero for the Level 0 (L0) closure test and close to one for the Level 2 (L2) closure test. These results indicate that our fitting methodology is adequate to reproduce the input FFs without introducing any significant procedural bias
Summary
All these determinations were performed at next-to-leading order (NLO) accuracy in perturbative QCD Their primary focus was put on quantifying the effects of the inclusion of new measurements, in the HKKS and JAM fits these were limited to SIA. Theoretical investigations of the effect of next-to-next-to-leading order (NNLO) QCD corrections [24], of a general treatment of heavy-quark mass effects [25], and of all-order small-z resummation [26] were performed in the framework of the DEHSS analyses, only for the SIA production of charged pions Despite this progress, available determinations of FFs are still potentially affected by some sources of procedural bias, the size and effect of which are difficult to quantify. [27,28], here we present NNFF1.0, a new determination of the FFs of charged pions, charged kaons, and protons/antiprotons from a comprehensive set of SIA measurements This analysis is performed at leading order (LO), NLO, and NNLO accuracy in perturbative QCD. The delivery of the NNFF1.0 sets is discussed in Appendix A
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