PDF sets and configuration

PDFxTMDLib reads collinear and transverse-momentum-dependent distributions from set directories. Each set contains metadata plus one or more numbered grid members.

Concepts and notation

Quantity Meaning
x Longitudinal momentum fraction; dimensionless.
μ2 Factorization scale squared, normally supplied in GeV2.
kT2 Transverse momentum squared for TMD evaluations, normally supplied in GeV2.
Member index Selects the central or an error/replica member of a set.

The examples on this website use member 0 as the central member for the named sets.

Grid formats

Collinear PDF sets

PDFxTMDLib reads the standard LHAPDF-style directory and grid organization used by collinear PDF sets. A typical set contains one .info file and numbered .dat members.

TMD sets

The lhagrid_tmd1 format generalizes the lhagrid1 grid concept to include the additional transverse-momentum dimension. A TMD grid therefore depends on x, kT2, μ2, and flavor.

A small generator example is available from the Downloads page.

Directory layout

Place every set inside a parent data directory:

PDFxTMD_PATH/
└── <set-name>/
    ├── <set-name>.info
    ├── <set-name>_0000.dat
    ├── <set-name>_0001.dat
    └── ...

For example:

/home/user/pdf-data/CT18NLO/CT18NLO.info
/home/user/pdf-data/CT18NLO/CT18NLO_0000.dat

The API receives the set name only:

PDFxTMD::PDFSet<PDFxTMD::CollinearPDFTag> set("CT18NLO");

Configure search paths

PDFxTMDLib reads a config.yaml file from:

  • Windows: C:\ProgramData\PDFxTMDLib\config.yaml
  • Linux and macOS: ~/.PDFxTMDLib/config.yaml

Add one or more parent directories:

paths:
  - /home/user/pdf-data
  - /work/shared/tmd-sets

On Windows, quote paths when backslashes or spaces could be ambiguous:

paths:
  - "D:/physics/PDF sets"
  - "C:/Users/Ramin/PDFxTMD-data"

The configured directories are searched together with the library’s current-directory and platform-default locations.

Important: add the parent directory, not the set directory itself. For a set stored at /home/user/pdf-data/CT18NLO/, add /home/user/pdf-data to paths:.

TMD sets linked from this website

The Downloads page is configured for the following archives:

  • 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

Download them from TMD set downloads. Collinear sets are available through the LHAPDF set index.

Validate a set installation

Before debugging application code, confirm that:

  1. The directory name matches the set name passed to PDFxTMDLib.
  2. The .info filename uses the same set name.
  3. Member files use four-digit indices such as _0000.dat.
  4. The parent directory appears in config.yaml.
  5. The requested member index exists.

Custom formats and numerical components

Applications are not limited to the default grid readers. Advanced users can provide compatible reader, interpolator, and extrapolator components and combine them through the generic C++ interfaces. See the advanced C++ example and the API reference.