APFEL: A PDF evolution library with QED corrections

Quantum electrodynamics and electroweak corrections are important ingredients for many theoretical predictions at the LHC. This paper documents APFEL, a new PDF evolution package that allows for the first time to perform DGLAP evolution up to NNLO in QCD and to LO in QED, in the variable-flavor-number scheme and with either pole or (MS) over bar heavy quark masses. APFEL consistently accounts for the QED corrections to the evolution of quark and gluon PDFs and for the contribution from the photon PDF in the proton. The coupled QCD circle times QED equations are solved in x-space by means of higher order interpolation, followed by Runge-Kutta solution of the resulting discretized evolution equations. APFEL is based on an innovative and flexible methodology for the sequential solution of the QCD and QED evolution equations and their combination. In addition to PDF evolution, APFEL provides a module that computes Deep-Inelastic Scattering structure functions in the FONLL general-mass variable-flavor-number scheme up to 0 (alpha(2)(s)). All the functionalities of APFEL can be accessed via a Graphical User Interface, supplemented with a variety of plotting tools for PDFs, parton luminosities and structure functions. Written in FORTRAN 77, APFEL can also be used via the C/C++ and Python interfaces, and is publicly available from the HepForge repository. Program summary Program title: APFEL Catalogue identifier: AESQ_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AESQ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 163479 No. of bytes in distributed program, including test data, etc.: 2164619 Distribution format: tar.gz Programming language: Fortran 77, C/C++ and Python. Computer: All. Operating system: All. RAM: <= 2 MB Classification: 11.6. External routines: LHAPDF Nature of problem: Solution of the unpolarized coupled DGLAP evolution equations up to NNLO in QCD and to LO in QED in the variable-flavor-number scheme, both with pole and with MSbar masses. Solution method: Representation of parton distributions and splitting functions on a grid in x, discretization of DGLAP evolution equations and higher-order interpolation for general values of x, numerical solution of the resulting discretized evolution equations using Runge-Kutta methods. Restrictions: Smoothness of the initial conditions for the PDF evolution. Running time: A few seconds for initialization, then similar to 0.5 s for the generation of the PDF tables with combined QCD circle times QED evolution (on a Intel(R) Core(TM)2 Duo CPU E6750 @ 2.66 GHz).