First measurement of the tensor analysing power T20 in inelastic (d, d′)X scattering at O° on 1H and 12C at 4.5 and 5.5 GeV/c

First results for T 20 of the inelastic ( d , d ′) X reaction above the Δ threshold are presented. It is observed that T 20 is negative; its absolute value is small in the Δ region and rises almost linearly to |T 20 | ⋍ (0.4–0.6) at energy transfers Q ⋍ 1 GeV. No significant dependence on the type of the target and on the initial energy was observed.