Entity definitions for elementary particles

In texts on high energy physics frequently re-occurring strings are the names of elementary particles. For example, the particle can be coded in various different ways with LaTeX: $\mbox{Z}^0$, $\mathrm{Z^0}$ and Z$^0$ all achieve the same typographical effect, a roman Z with a superscript 0. In the interest of standardization and typing convenience, we propose below an ``entity'' naming scheme, which will not only relieve the user from having to worry about the correctness of what he types, but also will allow an automatic extraction of the particle names from the input file, so that it will be easy to enter data about an article using this convention into a database of abstracts.

The naming scheme uses a notation which takes the following constraints into consideration:

1. The notation should be able to describe all particles in the particle data summary tables from the ``Review of Particle Properties''[3] and any future extension to these.
2. The names should not exceed eight characters. This is the maximum length for entities in the SGML reference concrete syntax[4]. Staying within this limit means that the notation can be used with most SGML applications.
3. Common particles such as protons and electrons should have short and simple names.
4. Items that are indicated by superscripts are indicated before items that are indicated by subscripts.

Due to the eight character limitation the mass could not be added to the name. This means that in general an entity on its own is not adequate to unambiguously identify a particle, c.f. (549) and (1300) are both referred to as Pgh. Including mass dependences into the names is not a good idea anyway, since the mass can change with time when more precise measurements become available. The ambiguity was solved by adding a letter to the end of the name where a mass appears in the name in the particle data summary tables. Thus (549) is referred to as Pgh while (1300) is referred to as Pgha. Higher letters correspond to higher masses, in the order given in the tables.

The PEN scheme is independent of any text processing system. We have implemented it in TeX (in such a way that it may be used in all macro packages, e.g. LaTeX) and SGML. The TeX implementation will print particle masses, which will be regularly updated according to the Review of Particle Properties publication. It is constructed so that the PEN name can be used both in mathematics and text mode.

• Principles of the Particle Entity Notation (PEN)
• Particle encodings according to the PEN Scheme