Proton and deuteron structure functions in muon scattering at 470 GeV

The proton and deuteron structure functions F₂ᵖ and F₂ᵈ are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991 and 1992 using liquid hydrogen and deuterium targets. The F₂ measurements are reported in the range $0.0008<x<0.6$ and 0.2<Q²<75 GeV². These are the first precise measurements of F₂ in the low x and Q² range of the data. In the high x range of the data where they overlap in x and Q² with the measurements from NMC, the two measurements are in agreement. The E665 data also overlap in x with the DESY HERA data, and there is a smooth connection in Q² between the two data sets. At high Q² the E665 measurements are consistent with QCD-evolved leading twist structure function models. The data are qualitatively described by structure function models incorporating the hadronic nature of the photon at low Q². The Q² and the W dependence of the data measure the transition in the nature of the photon between a pointlike probe at high Q² and a hadronic object at low Q².