Global analysis of fragmentation functions to charged hadrons with high-precision data from the LHC

TL;DR

This paper presents a comprehensive global analysis of fragmentation functions for charged hadrons using high-precision LHC data, improving constraints on gluon and quark FFs with methodological advances and providing publicly available results.

Contribution

It introduces a novel global NLO QCD analysis incorporating LHC jet data, advanced fitting techniques, and uncertainty estimation, enhancing the precision of fragmentation functions.

Findings

Fragmentation functions are well constrained down to low momentum fractions.

Gluon and quark FFs carry about 50% of the parton momentum at low fractions.

The analysis achieves a good fit with $\,\chi^2/N_{pt}\sim 0.90$.

Abstract

Fragmentation functions (FFs) are essential non-perturbative QCD inputs for predicting hadron production cross sections in high energy scatterings. In this study, we present a joint determination of FFs for light charged hadrons through a global analysis at next-to-leading order (NLO) in QCD. Our analysis incorporates a wide range of precision measurements from the LHC, as well as data from electron-positron collisions and semi-inclusive deep inelastic scatterings. By including measurements of jet fragmentation at the LHC in our global analysis, we are able to impose strong constraints on the gluon FFs. A careful selection of hadron kinematics is applied to ensure the validity of factorization and perturbative calculations of QCD. In addition, we introduce several methodological advances in fitting, resulting in a flexible parametrization form and the inclusion of theoretical uncertainties from perturbative calculations. Our best-fit predictions show very good agreement with the global data, with $\chi^2/N_{pt}\sim 0.90$. We also generate a large number of Hessian error sets to estimate uncertainties and correlations of the extracted FFs. FFs to charged pions (kaons and protons) are well constrained for momentum fractions down to 0.01 (0.1). Total momentum of partons carried by light charged hadrons are determined precisely. Their values for $u$, $d$ quarks and gluon saturate at about 50\% for a lower cut of the momentum fraction of 0.01. Pulls from individual datasets and impact of various choices of the analysis are also studied in details. Additionally, we present an update of the FMNLO program used for calculating hadron production cross sections. Our FFs, including the error sets (denoted as NPC23), are publicly available in the form of LHAPDF6 grids.