Atomic-weight dependence of muon-pair production in 225-GeV/cπ−-nucleus interactions

In an experiment performed at Fermi National Accelerator Laboratory, the production of massive muon pairs in 225-GeV/c ${\pi }^{-}$-nucleus interactions has been studied for four nuclear targets. Comparison of the relative cross sections enables the dependence on atomic weight $A$ to be determined. If this dependence is parametrized such that the dimuon production cross section ${\sigma }_{\mu \mu }$ is proportional to $A^{\alpha }$ this experiment yields $\alpha =0.98\mathrm{}\pm 0.04$ for $4<\mathrm{}{m}_{\mu \mu }<8.5\mathrm{}$ GeV/${\mathit{c}}^2$, where $m_{\mu \mu }$ is the invariant mass of the muon pair.