Measurement of the ratios of deep inelastic muon-nucleus cross sections on various nuclei compared to deuterium

Results are presented on the ratios of the deep inelastic muon-nucleus cross sections for carbon, copper and tin nuclei to those measured on deuterium. The data confirm that the structure functions of the nucleon measured in nuclei are different from those measured on quasi-free nucleons in deuterium. The kinematic range of the data is such that 〈Q²〉 ∼ 5 GeV² at x ∼ 0.03, increasing to 〈Q²〉 ∼ 35 GeV² for x ∼ 0.65. The measured cross section ratios are less than unity for x ≲ 0.05 and for 0.25 ≲ x < 0.7. The decrease of the ratio below unity for low x becomes larger as A increases as might be expected from nuclear shadowing. However, this occurs at relatively large values of Q² (∼ 5 GeV²) indicating that such shadowing is of patrionic origin.