A Higher Order Perturbative Parton Evolution Toolkit (HOPPET)

Abstract

This document describes a Fortran 95 package for carrying out DGLAP evolution and other common manipulations of parton distribution functions (PDFs). The PDFs are represented on a grid in x-space so as to avoid limitations on the functional form of input distributions. Good speed and accuracy are obtained through the representation of splitting functions in terms of their convolution with a set of piecewise polynomial basis functions, and Runge-Kutta techniques are used for the evolution in Q. Unpolarised evolution is provided to NNLO, including heavy-quark thresholds in the MSbar scheme, and longitudinally polarised evolution to NLO. The code is structured so as to provide simple access to the objects representing splitting functions and PDFs, making it possible for a user to extend the facilities already provided. A streamlined interface is also available, facilitating use of the evolution part of the code from F77 and C/C++.Comment: 60 pages, 5 figures. Code available from http://projects.hepforge.org/hoppet

CT10 next-to-next-to-leading order global analysis of QCD

“…Our fitting code implements these NNLO Wilson coefficient functions in the S-ACOT-χ scheme together with the HOPPET program for the evolution of α s and PDFs [55], in which the switching points between the active flavors can be expressed in terms of either the MS masses or the pole masses. The fitting program can read either the pole masses or the MS masses as an input.…”

Evolution of the helicity and transversity. Transverse-momentum-dependent parton distributions

“…This means also that the gluon TMD cannot be studied via scaling violations at least at this order. We perform DGLAP evolution for the collinear functions f 1 (x, µ b ), g 1 (x, µ b ), h 1 (x, µ b ) using the HOPPET evolution package [48].…”

Multiple parton scattering in nuclei: Modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution for fragmentation functions

“…In the following we will numerically solve the mDGLAP evolution equations for the modified fragmentation functions using a modified HOPPET (Higher Order Perturbative Parton Evolution Toolkit) [44] in LO. HOPPET is a Fortran95 package with the GNU Public License that carries out the vacuum DGLAP evolution in z-space using Runge-Kutta method with a given initial condition D a (z, Q 2 0 ).…”