A-dependence of η-meson inclusive production at 10.5 GeV/ c

The experimental results are presented for ratios of ν-meson inclusive differential cross sections in 10.5 GeV/ c π ⁺p, π ⁺D and π ⁺A collisions, R_D/p=(d σ/d x_F)( π⁺D→ ηX)/ (d σ/d x_F) π⁺p→ ηX), R_A=(d σ/d x_F)( π⁺D→ ηX) in the beam fragmentation region. The results are based on the statistics of ≈ 5 × 10 ⁴ detected η → 2 γ decays. It is shown that the power α in the parametrisation R_A ≈ A^{α( xf)} does not change significantly with x_F and its mean value is 0.50±0.02. The lower limit is obtained for the effective coefficient with string tension in the colour string model, κ ⩾ 3 GeV/fm. The observed growth of R_A with x_F can be explained by an assumption of a neutron halo with the factor H ≈ 4 in the nuclei.