Accurate measurement of $F_{2}^{\rm d}/F_{2}^{\rm p}$ and $R^{\rm d} - R^{\rm p}$

Results are presented for $F_{2}^{\rm d}/F_{2}^{\rm p}$ and $R^{\rm d} - R^{\rm p}$ from simultaneous measurements of deep inelastic muon scattering on hydrogen and deuterium targets, at 90, 120, 200 and 280 GeV. The difference $R^{\rm d} - R^{\rm p}$, determined in the range $0.002<x<0.4$ at an average $Q^{2}$ of 5 GeV$^{2}$, is compatible with zero. The $x$ and $Q^{2}$ dependence of $F_{2}^{\rm d}/F_{2}^{\rm p}$ was measured in the kinematic range $0.001<x<0.8$ and $0.1<Q^{2}<145$ GeV$^{2}$ with small statistical and systematic errors. For $x>0.1$ the ratio decreases with $Q^{2}$.