SMALL-X STRUCTURE FUNCTIONS FROM NMC

The NMC measurements of the proton and deuteron structure functions fo r 0.006 < x < 0.6 and 0.5 < Q2 < 55 GeV2 and of the neutron-to-proton structure function ratio down to x = 0.0008 are presented. The data ag ree very well with the earlier results of the BCDMS, SLAC (reanalysed) and EMC NA28 experiments, but disagree with the reanalysed results of the EMC NA2. A parametrization of the low-x structure function F2, in corporating vector meson dominance dynamics and the QCD-improved parto n model, valid at arbitrary Q2 and reproducing well the data, is also presented. Results of a quantitative analysis of the shadowing effect in the deuteron are given. The shadowing is found to be about a 2% eff ect, in qualitative agreement with the NMC results on the neutron-to-p roton structure function ratio at low x. The NMC results on the Q2 dep endence of the structure functions are compared with the predictions o f perturbative QCD in next-to-leading order. Parton distributions and the strong coupling constant are determined from the data. The QCD evo lution in the low-x region is driven largely by gluons, and shows only a moderate contribution of 'higher twists' at scales around 1 GeV2.