CT18 parton distribution functions

This page provides numerical table files for the computation of CT18 next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) parton distribution functions. They can be interpolated with the help of a standalone Fortran interface and demonstration program , as well as the tables with interpolated values of the QCD coupling alpha_s and PDFs. A simple C++ interface for the CTEQ-TEA PDFs with CTEQ6.6 or later can be found here.

Parametrizations of CT18 PDFs are also available from the LHAPDF library, version 6. For backward compatibility, we also provide CT18 grids in the LHAPDF5 format. Note that, in order to call all 59 CT18 error PDF sets with LHAPDF 5.9.X, you must recompile LHAPDF with an updated CT wrapper.

ATTENTION: The format of the PDF table files (with the extension .pds) and the Fortran interface were revised in 2012 to provide interpolation of the energy dependence of the QCD running coupling alpha_s using a table of alpha_s values stored inside the .pds file. The pre-2012 PDF table files are partly incompatible with the new format. They can be interpolated by the 2012 interface, but without computing alpha_s.

Available PDF sets

See the header of the Fortran interface for further explanations.

PDF set	Description and links to the table files	Authors or main contact	References	Date	Additional resources
CT18 NNLO	General-purpose NNLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Plots of L2 sensitivities Additional figures
CT18 NLO	General-purpose NLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18Z NNLO	General-purpose NNLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Plots of L2 sensitivities Additional figures
CT18Z NLO	General-purpose NLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18A NNLO	General-purpose NNLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18A NLO	General-purpose NLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18X NNLO	General-purpose NNLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18X NLO	General-purpose NLO central set + 58 eigenvector sets ( LHAPDF6, LHAPDF5 ) PDF sets with a varied strong coupling alpha_s(M_Z) in the ranges 0.116-0.120 and 0.110-0.124. The recommended 90% C.L. uncertainty estimate is 0.116 - 0.120.	T.-J. Hou et al.	arXiv:1912.10053	12/2019	Additional figures
CT18qed (recommended)	General-purpose 1 central + 58 Hessian sets + 28 low-Q2 sets (LHAPDF6) Hessian sets are defined as 90% C.L., and low-Q2 sets are symmetrized and scaled to 90% C.L. Photon PDF are initialized at mu0=3 GeV (pQCD matching scale) with LUX formula and evolved to higher scales.	K. Xie et al.	arXiv:2106.10299	06/2021
CT18qed1(.3)GeV	General-purpose 1 central + 58 Hessian sets + 28 low-Q2 sets (LHAPDF6) Hessian sets are defined as 90% C.L., and low-Q2 sets are symmetrized and scaled to 90% C.L. Photon PDF are initialized at mu0=1.3 GeV (CT18 PDF starting scale) with LUX formula and evolved to higher scales	K. Xie et al.	arXiv:2106.10299	06/2021
CT18lux	General-purpose 1 central + 58 Hessian sets + 28 low-Q2 sets (LHAPDF6) Hessian sets are defined as 90% C.L., and low-Q2 sets are symmetrized and scaled to 90% C.L. Photon PDF are calculated with the LUX formalism at all scales.	K. Xie et al.	arXiv:2106.10299	06/2021
CT18LO	*General-purpose 1 central ( LHAPDF6 )	M. Yan et al.	arXiv:2205.00137	05/2022	Additional Figures
CT18FC	CT18FC NNLO fitted charm series; 4 model scenarios, each with 3 sets for Δχ²=0, 10, and 30; mem=0-2: CT18 BHPS3; mem=3-5: CT18 MBMC; mem=6-8: CT18 MCME; mem=9-11: CT18X BHPS3 (LHAPDF6)	M. Guzzi, T. J. Hobbs, K. Xie, J. Huston, P. Nadolsky, C.-P. Yuan	arXiv:2211.01387	11/2022
CT18qed neutron	CT18qed neutron (total, elastic, inelastic) CT18qed proton (updated) (total, elastic, inelastic)	K. Xie, B. Zhou, T.J. Hobbs	arXiv:2305.10497	05/2023

Families of PDFs: CTEQ6-CTEQ6.6, CT10, CT14.
In the S-ACOT-MPS project, we collect all the subtracted PDFs designed for the heavy-flavor hadroproduction.
Web support:
Tie-Jiun Hou (tjhou at msu.edu)
Pavel Nadolsky (nadolsky at smu.edu)
Keping Xie (xiekeping at pitt.edu)
C.-P. Yuan (yuan at pa.msu.edu)

This website is partially supported by the U.S. Department of Energy under Grants DE-SC0010129, DE-FG02-95ER40896 and by the U.S. National Science Foundation under Grants PHY-1719914, PHY-2013791, PHY-1820760, PHY-1820818.