Production ofμ-Meson Pairs by Photons

Abstract

Further measurements are reported on the anisotropic component of ${\mu }^{-}$ mesons from bombardment of an aluminum target by 600-Mev bremsstrahlung. As reported previously, we interpret such a forward peaking as evidence for the direct electromagnetic production of muon pairs. Combining our new data with those previously reported, we obtain a value of 1.42±0.34 (standard deviation) for the ratio of the observed negative-muon cross section to that calculated by assuming the muons to originate as spin-½ pair fragments from electromagnetic production in the Coulomb field of an aluminum nucleus of finite size. The absolute normalization is believed correct to within a factor of 1.4. However, the theoretical value considers only the contribution from processes leaving the aluminum nucleus in its ground state; inelastic processes could raise the theoretical value by 40%.