Muon spectra at La Jolla

Data obtained from the muon spectrometer at the University of California at San Diego are summarized, considering the zenith angle dependence of the muon flux. The muon spectrometer, which employs an 80-ton iron magnet to achieve a maximum detectable energy of 2 TeV and a magnetic deflection of 1.1 GeV/c and can be rotated to all zenith angles is described, and the energy spectra obtained for different angles are indicated. An expression for the differential spectrum as a function of the cosine of the zenith angle at the upper atmosphere production point is presented and shown to conform to experimental data for energies from 25 GeV to 2.0 TeV, with a spectral index of 2.715. A plot of the data from all zenith angles converted into a vertical spectrum is shown to indicate an excess of high-energy events over that predicted by the power law model, possibly due to kaon parent effects. It is concluded that measurements of the zenith angle dependence of the muon flux can provide a useful method of determining the spectral index