QCD evolution of superfast quarks

Recent high-precision measurements of nuclear deep inelastic scattering at high x and moderate 6 < Q(2) < 9 GeV2 give a rare opportunity to reach the quark distributions in the superfast region, in which the momentum fraction of the nucleon carried by its constituent quark is larger than the total fraction of the nucleon at rest, x > 1. We derive the leading-order QCD evolution equation for such quarks with the goal of relating the moderate-Q(2) data to the two earlier measurements of superfast quark distributions at large 60 < Q(2) < 200 GeV2. Since the high-Q(2) measurements gave strongly contradictory estimates of the nuclear effects that generate superfast quarks, relating them to the high-precision, moderate-Q(2) data through QCD evolution allows us to clarify this long-standing issue. Our calculations indicate that the moderate-Q(2) data at x less than or similar to 1.05 are in better agreement with the high-Q(2) data measured in (anti)neutrino-nuclear reactions which require substantial high-momentum nuclear effects in the generation of superfast quarks. Our prediction for the high-Q(2) and x > 1.1 region is somewhat in the middle of the neutrino-nuclear and muon-nuclear scattering data.