Polarization of Cosmic-RayμMesons

This paper reports: (1) measurements of the decay asymmetry of positive cosmic-ray muons which come to rest in a brass absorber at sea level under 12, 200, 700 and 3700 g/${\mathrm{cm}}^2$, air equivalent, of material; and (2) a determination of limits on the possible change with energy of the kaon-pion production ratio in nuclear interactions at energies from about 10 BeV to about 100 BeV. The measurements give values of the nominal polarization equal to 0.23±0.03, 0.16±0.02, 0.23±0.03, and 0.21±0.02 in order of increasing depth. The actual polarization is somewhat higher because of unevaluated systematic errors (e.g., electron scattering) which depend upon the details of construction of a given detector. The ratios of the polarizations observed at the different depths were compared with those computed under the assumption that the relative production rate of ${K_{\mu 2}}^{+}$ and ${\pi }^{+}$ mesons per unit energy interval varies with energy according to the relation $\frac{K\left(E\right)\mathrm{}}{\pi \mathrm{}\left(E\right)\mathrm{}}\propto {\mathrm{}(0.3+E)\mathrm{}}^{\delta }$, where E is the total energy measured in BeV and $\pi \mathrm{}\left(E\right)\mathrm{}\propto {\mathrm{}(0.3+E)\mathrm{}}^{-2.64\mathrm{}}$. We find that the data can be fitted to this relation for any value of $\delta$ between $-\infty$ and +0.6. This result is rather insensitive to changes in the constants 0.3 and 2.64 and is based upon the assumptions that: (1) there is a negligible anomalous depolarization of the muons as they traverse the material above the detectors, and (2) the muons arise only from the decays of pions and charged kaons. If charged and neutral kaons are produced in equal numbers, the upper limit for $\delta$ would be raised to about 1.3.