Improved nonsinglet QCD analysis of the fixed-target DIS data

Deep inelastic scattering data on $F_2$ structure function obtained by BCDMS, SLAC and NMC collaborations in fixed-target experiments were analyzed in the non-singlet approximation with next-to-next-to-leading-order accuracy. The strong coupling constant is found to be $\alpha_s(M_Z^2) = 0.1157 \pm 0.0022 (total,,,exp.error) + \biggl{\begin{array}{l} +0.0028 \ -0.0016 \end{array} (theor)$, which is seen to be well compatible with the average world value. Results obtained in the present paper by carrying out fits similar to those done in our earlier study, with the exception for systematic errors in BCDMS data taken into account in a different way, confirm those which were derived in that same paper.