Measurement of the Polarization of \(\varLambda^{0}\) Hyperons Produced Inclusively by 12-GeV Protons on Tungsten

Abstract

The polarization of 2.4×10 5 \(\varLambda^{0}\) hyperons has been measured in inclusive production by 12- GeV protons on tungsten at three production angles, 3.5°, 6.5°, and 9.5°. In terms of Feynman's x F and the transverse momentum p T of \(\varLambda^{0}\), the kinematic range is 0.3≦ x F ≦0.8 and 0.4≦ p T ≦1.6 GeV/c. The \(\varLambda^{0}\) was identified by detecting the proton and pion from the \(\varLambda^{0}{\rightarrow}p\pi^{-}\) decay with a double-stage magnetic spectrometer, and its polarization was determined from a hybrid Monte Carlo analysis on asymmetries in the angular distribution of the decay products. The observed polarization is consistent with the data obtained at higher energies, indicating that the phenomenon of the inclusive \(\varLambda^{0}\) polarization scales down to the 12-GeV region. The polarization at 12 GeV increases linearly with p T up to 16% at p T =1.0 GeV/c, showing a tendency to level off above that point.