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MRS  structure functions

The MRS  group also presents several sets of proton structure functions. Two of them are implemented in CompHEP. They are MRS($A^\prime$) and MRS($G$) [MRS-1995].

In the $A^\prime$ case it is supposed that the sea quark and gluon densities are parameterized at small $x$ by the $x^{-\lambda}$ function where $\lambda$ is the same for the gluon and for the sea quarks. This suggestion is motivated by the QCD theory. The G set uses two different $\lambda$ parameters for the sea quarks and for the gluon densities. A fit of experimental data for the G set is better.

The next-to-leading order evaluation and the $\overline{MS}$ factorization scheme are used for evaluation of the $Q^2$ dependence of structure function. $\alpha_s(M_Z) = 0.113 \; [0.114]$ in the $A^\prime$ [$G$] case, correspondingly.

The available range is

$$\begin{array}{lcl} 10^{-5} & < x < & 1; \\ 5 & < Q^2 < & 1310720 \;\mbox{GeV}^2. \end{array}$$

See complete explanation in [MRS-1995].