New parton distribution functions of the real photon
Abstract
Precise determination of the partonic structure of real photons has attracted renewed interest in view of ongoing studies of high-energy photon-induced processes in ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) and the future Electron-Ion Collider (EIC). Despite being fundamental in their own right and essential for QCD phenomenology of hard processes initiated by resolved photons, the quark and gluon distributions of the photon are poorly known and merit a new analysis employing modern tools of statistical data analysis. We determine new sets of leading-order (LO) and next-to-leading-order (NLO) parton distributions (PDFs) for the real photon, dubbed VALO1.0, by performing a global QCD analysis of the world data on the photon structure function F2γ measured in deep-inelastic scattering (DIS) processes on a real photon target in electron-positron collisions. Our analysis improves on the results available in the literature by providing uncertainties in the form of Monte Carlo replicas and the photon PDFs in the LHAPDF6 format. We observe that while the electron-positron data allow us to determine the singlet quark distribution very well at both LO and NLO, the gluon distribution is constrained to a much lesser degree, especially at LO. For this analysis, we have developed an open-source framework, which extends the pineline framework, developed for the proton, to the photon case and includes the program solving the inhomogeneous scale evolution of photon PDFs, γEKO.
Related
- Parton distribution functions and strong coupling constant: MSHT
- Parton Distribution Functions from Large Momentum Expansion of Current-Current Correlators
- Third moments of nucleon unpolarized, polarized, and transversity parton distribution functions from physical-point lattice QCD
- Quasi Parton Distribution Functions in Covariant Quark Models
- Mathematical inverse problem for the world data inference of the parton distribution functions of the proton
BibTeX
@misc{chithirasreemadam2026parton,
title = {{New parton distribution functions of the real photon}},
author = {Madhav Chithirasreemadam and Vadim Guzey and Felix Hekhorn and Ilkka Helenius and Hannu Paukkunen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17163},
eprint = {2609.17163},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17163},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - New parton distribution functions of the real photon
AU - Madhav Chithirasreemadam
AU - Vadim Guzey
AU - Felix Hekhorn
AU - Ilkka Helenius
AU - Hannu Paukkunen
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17163
UR - https://arxiv.org/abs/2609.17163
AB - Precise determination of the partonic structure of real photons has attracted renewed interest in view of ongoing studies of high-energy photon-induced processes in ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) and the future Electron-Ion Collider (EIC). Despite being fundamental in their own right and essential for QCD phenomenology of hard processes initiated by resolved photons, the quark and gluon distributions of the photon are poorly known and merit a new analysis employing modern tools of statistical data analysis. We determine new sets of leading-order (LO) and next-to-leading-order (NLO) parton distributions (PDFs) for the real photon, dubbed VALO1.0, by performing a global QCD analysis of the world data on the photon structure function F_2^γ measured in deep-inelastic scattering (DIS) processes on a real photon target in electron-positron collisions. Our analysis improves on the results available in the literature by providing uncertainties in the form of Monte Carlo replicas and the photon PDFs in the LHAPDF6 format. We observe that while the electron-positron data allow us to determine the singlet quark distribution very well at both LO and NLO, the gluon distribution is constrained to a much lesser degree, especially at LO. For this analysis, we have developed an open-source framework, which extends the pineline framework, developed for the proton, to the photon case and includes the program solving the inhomogeneous scale evolution of photon PDFs, γEKO.
ER -