PDF Set Selection in PDFxTMDLib

PDFxTMDLib uses a standardized approach for PDF set organization and selection. This page explains the file formats, directory structure, and configuration options for working with PDF sets.

PDF Set File Format

PDFxTMDLib does not introduce any new file format for collinear PDF sets, and instead follows the standard LHAPDF format. However, because currently there is no standard in TMDs and TMDLib, PDFxTMDLib extends the LHAPDF format (lhapdf1) to lhagrid_tmd1.

The lhagrid_tmd1 format is similar to lhapdf1 but with TMD sets generated in grids of x, kt², μ², and flavors for simplicity in only one subgrid. This is simpler than lhapdf1 which supports multiple subgrids in the form of x, μ², and flavors.

Supported TMD Sets

TMD Sets

PDFxTMDLib currently supports the following TMD sets:

  • PB-LO-HERAI+II-2020-set1
  • PB-LO-HERAI+II-2020-set2
  • PB-NLO+QED-HERAI+II-set1
  • PB-NLO+QED-HERAI+II-set2
  • PB-NLO-HERAI+II-2023-set2-qs=0.74
  • PB-NLO-HERAI+II-2023-set2-qs=1.04

You can download these TMD sets directly from our Downloads page where they are hosted on this website for faster access.

More TMD sets will be added in the future and announced on this website.

Collinear PDF Sets

PDFxTMDLib fully supports all LHAPDF sets. You can download collinear PDF sets directly from the LHAPDF website.

Directory Structure

The default folder structure for grid and info files is as follows:

PDFxTMD_PATH/<setname>/<setname>_<nnnn>.dat
PDFxTMD_PATH/<setname>/<setname>.info

Here, <nnnn> represents a four-digit number. For example, CT18NLO_0003.dat denotes the third member of the PDF set named CT18NLO.

Configuring PDF Set Search Paths

To add search paths for PDF sets, you can modify the config.yaml file located at:

  • Windows: C:\ProgramData\PDFxTMDLib
  • Linux: ~/.PDFxTMDLib

Add paths to the yaml file like this:

paths:
- /home/PDFxTMDSets1
- /home/PDFxTMDSets2

With this configuration, the library searches for cPDF and TMD sets in:

  1. The paths specified in config.yaml
  2. The current binary directory (where the executable resides)
  3. /usr/local/share/PDFxTMD_PATH (Linux) or C:\ProgramData\PDFxTMDLib (Windows)

Custom PDF Set Formats

If a PDF set does not conform to the default structure, you have two options:

  1. Adjust the set to align with the standard convention
  2. Implement a custom reader class to handle the non-standard format

Framework Extensibility

PDFxTMDLib is designed as a framework where libraries like LHAPDF and TMDLib can be subsets. Users can support their own cPDFs and TMDs by adding appropriate IReader, IInterpolator, and IExtrapolator subclasses, enabling support for any new file format required by specific groups.

PDFxTMDLib supports all the features of LHAPDF, including uncertainty, QCD coupling, and cPDF calculations. Due to its generic implementation, it also brings support for QCD coupling and uncertainty for the first time in the TMDs world.

In implementing PDFxTMDLib, the same code as LHAPDF is adopted for most calculations, but reorganized and improved for better performance within the PDFxTMDLib framework.