139with pions. If so, this could indicate a mode of production for heavy mesons different from that for pions. It may be noted, however, that heavy mesons of greater energy have been observed in cloud chamber work, but little is known about the energy spectrum at present. Powell 4 conjectures that the hyperons and heavy mesons may often originate from secondary interactions of pions (produced in nucleon-nucleon collisions) with other nucleons in the same nucleus. Evidence that hyperons and i£-mesons are created in the interaction of pions with hydrogen nuclei has been obtained in work with the Brookhaven Cosmotron. 8 Recent work on a very high-energy nuclear shower by 8 Fowler, Shutt, Thorndike, and Whittemore, Phys. Rev. 91, 1287 (1953).
As a test of muon-electron universality we have compared muon-proton and electron-proton inelastic scattering cross sections for lq21 (square of the four-momentum transferred from the lepton) values up to 4.0 (GeV/cj2 &d for lepton energy losses up to 9 GeV.There is no experimentally significant deviation from muon-electron universality.If the muon is assigned the form factor (1.0 +1q21 /A $-' relative to the electron, then with 97.7% confidence Ad > 4
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