  The two-body photodisintegration of $^4$He into a proton and a triton has
been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at Jefferson
Laboratory. Real photons produced with the Hall-B bremsstrahlung-tagging system
in the energy range from 0.35 to 1.55 GeV were incident on a liquid $^4$He
target. This is the first measurement of the photodisintegration of $^4$He
above 0.4 GeV. The differential cross sections for the $\gamma$$^4$He$\to pt$
reaction have been measured as a function of photon-beam energy and
proton-scattering angle, and are compared with the latest model calculations by
J.-M. Laget. At 0.6-1.2 GeV, our data are in good agreement only with the
calculations that include three-body mechanisms, thus confirming their
importance. These results reinforce the conclusion of our previous study of the
three-body breakup of $^3$He that demonstrated the great importance of
three-body mechanisms in the energy region 0.5-0.8 GeV .
