East-West Asymmetry of Positive and Negative Mesons at the Geomagnetic Equator

The intensities of positive and negative $\mu$ mesons at zenith angles of 45° in the east-west plane and at the vertical have been measured at atmospheric depth 548 g ${\mathrm{cm}}^{-2\mathrm{}}$ near the geomagnetic equator. The data are analyzed through use of the empirical production spectrum and unidimensional equation for $\mu$-meson production employed by Sands and by Olbert. A careful theoretical discussion is given, taking into account in detail the various effects arising both from the variation of the geomagnetic cutoff with direction of incidence of the primaries and from the curvature of the trajectories of the mesons in the earth's magnetic field after their production in the atmosphere. It is found that, to bring the 45° and vertical data into accord, it is necessary to assume an rms angle of production of the parent $\pi$ mesons of 14°±2°. It is then possible to express the production spectrum, at any geographical location, by the single equation $G\left(R^{\prime }\right)=A{[R^{\prime }+a(M_c\left)\right]}^{-n}$, where $M_c$ is the cutoff magnetic rigidity for the primaries in a given direction of incidence at that location. The data do not indicate the presence of any appreciable number of negatively charged particles in the primary cosmic radiation.