PDG database file

The PDG database file contains the data from one edition of the Review of Particle Physics in a single file in SQLite (version 3) format. Depending on what version of the file was obtained, Summary Table values from previous editions may also be included. The database file provides the default data store for the Python API and a copy is bundled with and installed when the Python API package pdg is installed.

Available database files can be downloaded from the the API page on the PDG website.

In contrast to the Python API, the database file provides relatively low-level access to PDG data. Its use requires not only the technical expertise for querying the PDG data in SQL, but also a good understanding of how PDG data is organized, how different flags are used, and how special cases have to be treated. The documentation in this chapter tries to provide the minimum information necessary to start using the database file. Users who wish to do so are encouraged to consult the source code of the Python API as a “reference implementation” to see how PDG data can be extracted. Please note that PDG can provide at best limited support for using the database file.

Database schema

The database file contains the following database tables:

  • pdgid is the lookup table for PDG Identifiers and provides the central index on what data is available. Data tables such as pdgdata use foreign keys to pdgid to specify the quantity for which data in a given row is provided. As a convenience to software developers and others querying the data, the PDG Identifiers (pdgid.pdgid) are duplicated in other data tables. Nevertheless, such tables should only be joined with table pdgid using the primary key pdgid.id of the pdgid table.

  • pdgdata contains the data provided in the Summary Tables of the Review of Particle Physics.

  • pdgparticle contains the mapping between PDG Identifiers and particle names, their Monte Carlo particle numbers, and additional information such as quantum numbers. pdgparticle contains a separate entry for each possible charge of a particle. The particle names in pdgparticle are the standard names in ASCII format following the PDG naming conventions.

  • pdgitem is a reference table that defines the unique names of all particles, aliases, shortcuts, sets of names, as well as any other strings used by the PDG API. The type of each entry is given by pdgitem.item_type. The possible types are documented in table pdgdoc (see below).

  • pdgitem_map provides a generic one-to-many mapping mechanism. It is used to define e.g. particle aliases, previously used particle names, as well as the mappings between generic particle names such as B (which do not specify a specific charge) and the actual particles this may designate (in this example, B+, B0, Bbar0, and B-).

  • pdgdecay provides for each decay (specified by it’s PDG Identifier) the incoming and outgoing particles. The multiplier entry is used to indicate if a particle or decay product appears multiple times. subdecay_id specifies that the given decay product needs to decay in a specific way. Concatenating the entries in pdgdecay for a given decay in the order given by sort results in the decay string as provided by the description of the corresponding PDG Identifier. Note that each decay product is a pdgitem that may or may not be mapped to one or several particles using pdgitem_map. However, not all decay products are mapped to individual particles. For example anything or X are used in inclusive decays to specify further decay products.

  • pdginfo provides metadata about the contents of the database file, such as the edition of the Review of Particle Physics from which the data was extracted, version and citation information.

  • pdgdoc serves as a documentation table for the different codes and flags used in other tables.

The figure below summarizes the database schema and the columns of each table. Arrows represent foreign key relations. Bold column names indicate constraints. Further details about the database file as well as examples of how to use it will be provided in the future.

Schema of the SQLite database file

Usage example

To give a concrete example of how the PDG SQLite database files could be used, the SQL snippet below produces a table of branching fractions for the charged pion.

SELECT pdgid.pdgid,
       description,
       value AS branching_fraction,
       limit_type,
       value_type
FROM   pdgid
       JOIN pdgdata
         ON pdgdata.pdgid_id = pdgid.id
WHERE  pdgid.parent_pdgid = 'S008'
       AND data_type = 'BFX'
       AND edition = '2024'
ORDER  BY pdgid.sort;

In this example:

  • Tables pdgid and pdgdata are joined. The former is used to select and show the specific decay and the latter to get data values.

  • pdgid.parent_pdgid='S008' selects charged pions using their PDG Identifier.

  • data_type='BFX' selects exclusive non-indented branching fractions.

  • edition='2024' selects data from the 2024 edition (assuming this data is available in the SQLite file being used).

  • limit_type will either be NULL (in case a value is not a limit), or a code to denote the type of limit the corresponding value represents.

  • value_type is a code indicating whether this is an average, fit value, best limit etc.

  • Indented branching fractions are not included for two reasons: first, the parent_pdgid of an indented decay is the PDG Identifier of the higher-level decay (such as e.g. S008.1), and second its data_type will indicate the indentation (e.g. BFX1 instead of BFX).

  • value is the raw, numerical value without any rounding applied. To get the value rounded and formatted as shown in the PDG Summary Tables use display_value_text instead of value (which will also show the error and indicate limits). The pdgdata table of course also provides numerical values for errors, units, and more.

Specific values of flags and other codes such as the ones found in data_type, limit_type or value_typeare documented in table pdgdoc. For example, to see what values limit_type can have, one can use:

SELECT value,
       description
FROM   pdgdoc
WHERE  table_name = 'PDGDATA'
       AND column_name = 'LIMIT_TYPE';

which might produce

| value |                 description                 |
|-------|---------------------------------------------|
|       | NULL means not a limit (i.e. a measurement) |
| L     | lower Limit                                 |
| R     | range                                       |
| U     | upper Limit                                 |
| X     | range exclusion                             |

License

The data obtained from the PDG REST API is subject to the license used by the corresponding edition of the Review of Particle Physics. Starting with the 2024 edition, the Review of Particle Physics is published under a CC BY 4.0 license.