Measurement of Tensor Polarization and Cross Section for the ReactionH2(π+,π+)H2at 180°

Abstract

This Letter reports the first measurement of tensor polarization ($t_{20}$) in $\pi -d$ elastic scattering and also measurements of the $\pi -d$ elastic-scattering cross section at 180°. The measurements were performed using the low-energy pion channel at Clinton P. Anderson Meson Physics Facility and a novel high-efficiency deuteron polarimeter. The result of the polarization measurement, $t_{20}=-0.23\mathrm{}\pm 0.15$ at $T_{{\pi }^{+}}=140\mathrm{}$ MeV, is in disagreement with all theoretical predictions.