Parton distribution functions give the number of partons (quarks and gluons) in a high momentum proton or other hadron. Precisely, the parton distribution

gives the distribution of partons as a function of the variables a, A, x and mu. Parton distribution functions (in the "MS-bar" convention) are precisely defined in terms of matrix elements of operators. An introduction to parton distribution functions (200 Kbytes, gzipped Postscript) may prove useful. A set of notes from the 1996 SLAC Summer Institute on the basics of QCD perturbation theory (1000 Kbytes, gzipped Postscript) may also prove useful as background.

Parton distribution functions are determined from data from particle physics experiments. Several sets of parton distribution functions are available. In these pages, we provide information about parton distributions fitted to data by three groups, MRS, CTEQ, and GRV. Each group provides parton distributions in the form of a computer code. To see the differences among parton distributions, it is useful to make graphs.

In these pages, we provide computer code that can produce any of the parton distributions. The code interpolates the desired parton distribution function from a table written in a standard form. A brief explanation of the program that interpolates the parton data may be useful. There are some caveats.

### Parton distribution tables in the standard form

We also provide a somewhat more elaborate computer code that reads the data for several parton distribution sets, holds them all in memory, and interpolates from any of the tables as requested.

To produce the values of parton distribution functions from a parton distribution set not included here, one need only generate the parton table in the standard form.

One application of parton distributions is the calculation of the structure functions measured in deeply inelastic scattering. Code for such calculations is available from HEPDATA site at Durham. Another application is the calculation of cross sections to produce jets in hadron collisions. Code for this is available.

## Diffractive parton distributions

We also present a set of diffractive parton distributions from F. Hautmann and D. E. Soper, Phys. Rev. D 63, 011501 (2000). A diffractive parton distribution represents the probability to find a certain kind of parton in an incoming hadron under the condition that the hadron remains intact except for a small momentum transfer (as described in the reference above and references cited there). Diffractive parton distributions can be used to calculate diffractive deeply inelastic scattering.
Davison E. Soper and Parvez Anandam
Institute of Theoretical Science
University of Oregon
Eugene OR 97403. USA.
soper@physics.uoregon.edu