Polarization of Λ and Λ overbar in 920 GeV fixed-target proton–nucleus collisions

Abstract A measurement of the polarization of Λ and Λ ¯ baryons produced in p C and p W collisions at s = 41.6 GeV has been performed with the HERA-B spectrometer. The measurements cover the kinematic range of 0.6 GeV / c p ⊥ 1.2 GeV / c in transverse momentum and − 0.15 x F 0.01 in Feynman- x . The polarization results from the two different targets agree within the statistical error. In the combined data set, the largest deviation from zero, + 0.054 ± 0.029 , is measured for x F ≲ − 0.07 . Zero polarization is expected at x F = 0 in the absence of nuclear effects. The polarization results for the Λ agree with a parametrization of previous measurements which were performed at positive x F values, where the Λ polarization is negative. Results of Λ ¯ polarization measurements are consistent with zero.