Measurement of the proton and deuteron structure functions, $F_{2}^{p}$ and $F_{2}^{d}$, and of the ratio $\sigma_{L}/\sigma_{T}$

The muon-proton and muon-deuteron inclusive deep inelastic scattering cross sections were measured in the kinematic range $0.002 < x < 0.60$ and $0.5 < Q^{2} < 75$ GeV$^{2}$ at incident muon energies of 90, 120, 200 and 280 GeV. These results are based on the full data set collected by the New Muon Collaboration, including the data taken with a small angle trigger. The extracted values of the structure functions $F_{2}^{p}$ and $F_{2}^{d}$ are in good agreement with those from other experiments. The data cover a sufficient range of y to allow the determination of the ratio of the longitudinally to transversely polarised virtual photon absorption cross sections, $R= \sigma_{L}/\sigma_{T}$, for $0.002 < x < 0.12$. The values of $R$ are compatible with a perturbative QCD prediction; they agree with earlier measurements and extend to smaller $x$.