The scale dependent nuclear effects in parton distributions for practical applications

Abstract. The scale dependence of the ratios of parton distributions in a proton of a nucleus A and in the free proton, $R_i^A(x,Q^2)=f_{i/A}(x,Q^2)/f_i(x,Q^2)$, is studied within the framework of the lowest order leading-twist DGLAP evolution. By evolving the initial nuclear distributions obtained with the GRV-LO and CTEQ4L sets at a scale $Q_0^2$, we show that the ratios $R_i^A(x,Q^2)$ are only moderately sensitive to the choice of a specific modern set of free parton distributions. We propose that to a good first approximation, this parton distribution set-dependence of the nuclear ratios $R_i^A(x,Q^2)$ can be neglected in practical applications. With this result, we offer a numerical parametrization of $R_i^A(x,Q^2)$ for all parton flavours i in any $A>2$, and at any $10^{-6}\le x \le 1$ and any $2.25 {\rm GeV}^2\le Q^2\le 10^4\,{\rm GeV}^2$ for computing cross sections of hard processes in nuclear collisions.