Numerical solution of $Q^2$ evolution equations in a brute-force method

Abstract

We investigate numerical solution of $Q^2$ evolution equations for structure functions in the nucleon and in nuclei. (Dokshitzer-Gribov-Lipatov-)Altarelli-Parisi and Mueller-Qiu evolution equations are solved in a brute-force method. Spin-independent flavor-nonsinglet and singlet equations with next-to-leading-order ${\alpha }_s$ corrections are studied. Dividing the variables $x$ and $Q^2$ into small steps, we simply solve the integrodifferential equations. Numerical results indicate that accuracy is better than 2\% in the region $10^{-4}<x<0.8$ if more than two-hundred $Q^2$ steps and more than one-thousand $x$ steps are taken. The numerical solution is discussed in detail, and evolution results are compared with $Q^2$ dependent data in CDHSW, SLAC, BCDMS, EMC, NMC, Fermilab-E665, ZEUS, and H1 experiments. We provide a FORTRAN program for Q${}^2$ evolution (and ``devolution'') of nonsinglet-quark, singlet-quark, $q_i+{\bar{q}}_i$, and gluon distributions (and corresponding structure functions) in the nucleon and in nuclei. This is a very useful program for studying spin-independent structure functions.

Comments: 48 pages, LATEX, figs. 1-6. Complete postscript file including the figure is available at ftp://ftp.cc.saga-u.ac.jp/pub/paper/riko/quantum1/saga-he-81.ps.gz or at http://www.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.html (We had a problem in taking a file in WWW, but the problem was fixed recently.) Email: 94sm10 or kumanos@cc.saga-u.ac.jp