Scattering of 2-Bev/cMuons in Carbon and Lead

Abstract

The scattering cross section of high-energy $\mu$ mesons in carbon and lead has been measured, using a pure, monoenergetic beam of muons obtained with the Bevatron at the Lawrence Radiation Laboratory. Preparation, purification, and measured properties of the beam are described. The median momentum was 2.00±0.03 Bev/c, the spread in momentum was not more than ±3.5%, and the effective contamination due to pions was 4.9×${10}^{-6\mathrm{}}$. During the experiment the total number of muons incident on the apparatus was 2.5×${10}^7$. Counter hodoscopes recorded the muons scattered from 14.4 g/${\mathrm{cm}}^2$ of lead and from 27 g/${\mathrm{cm}}^2$ of carbon. Inelastic as well as elastic processes were accepted. Scattered particles were observed at angles up to 12° (momentum transfer ∼400 Mev/c). The lead data cover the same range as those cosmic-ray experiments which have appeared to indicate an anomalously large scattering. No anomaly is found; the lead scattering agrees closely with the distribution calculated by Cooper and Rainwater for purely electromagnetic interactions. The carbon data permit a better comparison with theoretical expectations, since one is measuring the single-scattering cross section directly, and one can account for the effects of nuclear structure rather accurately, using electron-scattering data and a detailed theoretical analysis of Drell and Schwartz. The carbon scattering results, based on 300 events in the region 70 Mev/c-400 Mev/c momentum transfer, agree closely with the Drell-Schwartz theory. The upper limits which this result places on a nonelectromagnetic scattering cross section and on a muon form factor are discussed.