Polarization of Cosmic-Ray Muons

Abstract

We have measured the polarization of cosmic-ray muons arriving at seal level with different energies and from different zenith angles. The polarization of positive muons from the zenith with energies near 1.0 GeV was found to be -0.33 \ifmmode\pm\else\textpm\fi{} 0.04, where the polarization in the direction of flight was measured and the negative sign indicates that the spin was antiparallel to the direction of flight. Muons from the zenith with energies near 3.5 GeV at sea level had polarizations of -0.38 \ifmmode\pm\else\textpm\fi{} 0.04, and the polarization of muons with energies near 4.5 GeV incident at an angle of 45\ifmmode^\circ\else\textdegree\fi{} with the zenith was found to be -0.34 \ifmmode\pm\else\textpm\fi{} 0.04. These polarizations are consistent with the polarizations calculated on the basis that the muons are derived almost wholly from the decay of pions produced by the interaction of primary and secondary cosmic-ray hadrons with the nuclei of the atmosphere.