Tests of the parametrizations of Fragmentation Functions using data on inclusive pion and kaon production in unpolarized $pp$ collisions from the STAR collaboration and at the NICA project

TL;DR

This study evaluates various pion and kaon fragmentation functions against STAR data at 200 GeV using NLO pQCD, finding certain sets fit well and providing predictions for future NICA collider experiments.

Contribution

It systematically compares multiple fragmentation functions with experimental data at high energy and assesses their suitability for predictions at lower NICA energies.

Findings

NLO fits better than LO, especially at small p_T.

Certain FF sets (LSS-15, DSEHS-14 for pions; DSEHS-17 for kaons) match experimental data well.

Pure pQCD approaches are insufficient at NICA energies, indicating the need for higher-order effects.

Abstract

The goal of this study is to check which, if any, of the published versions of the pion and kaon fragmentation functions is compatible with the STAR data on semi-inclusive pion and kaon production in proton-proton collisions, and on the basis of this analysis to make reliable predictions for the $p_T$ spectra of the pions and kaons in inclusive pion and kaon production at the future NICA proton-proton collider. The calculations are carried out in next-to-leading order (NLO) of perturbative quantum chromodynamics (pQCD), using the well tested CTEQ6 parton distributions. We consider the following pion and kaon fragmentation functions (FFs) -- DSEHS-14, DSEHS-17, LSS-15, HKNS-07 and AKK-08. Our analysis shows that within the experimental errors all tested sets of fragmentation functions provide a good fit to STAR data at the c.m. energy $ \sqrt{S} = 200\, {\rm GeV} $, and the best ones are both LSS-15 and DSEHS-14 for pions and DSEHS-17 for kaons. From comparison of the LO and NLO results it is clear that the latter fit data much better, specially in the region of small $p_T$. The NLO cross sections are also less scale-$Q^2$ dependent, where $p_T/2\leqslant Q \leqslant 2p_T$, than the LO ones. In order to make predictions for NICA energies, we compare the NLO pQCD results with the existing experimental BES STAR data on semi-inclusive hadron production in the most peripheral Au+Au collisions where the nuclear effects can be neglected. The comparison for lower energy scales, like at NICA, shows that a purely pQCD approach is inadequate and suggests the necessity to take into account also higher-order effects of initial-state soft-gluon radiation. Nevertheless, these data on the $p_T$ spectra of $\pi^+$, $K^+$ and also the ratios $\pi^-/\pi^+$ and $K^-/K^+$ seem favour LSS-15 and DSEHS-14 FFs for pions and DSEHS-17 for kaons, similarly as at the energy scale $ \sqrt{S} = 200\, {\rm GeV} $.