A measurement of Λ and polarization in inclusive production by of 340 GeV/c in C and Cu targets

We have measured the polarization of Λ hyperons produced inclusively by a Σ− beam of 340 GeV/c momentum in nuclear targets. From a sample of 9.5 millions of identified Λ decays, polarizations were determined in the range xF > 0.1 and pt ≤ 1.6 GeV/c. The polarization w.r.t. the production normal is mainly positive for xF ≥ 0.3. At fixed values of xF , it increases with pt to a maximum between pt=0.5 and pt=1 GeV/c , and then decreases to zero or even negative values, in sharp contrast to the plateau above pt=1 GeV/c observed in inclusive Λ production by protons.