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The neutral decay modes of the r) are observed by detecting the resulting y's in a leadplate spark-chamber array. The T)'s are produced in the reaction TT +p-~n +TJ, at 707 MeV/c. The neutron is detected with scintillators and its energy measured by a timeof flight technique. Our results for the neutral branching ratios are 2y = (57.9± 5.2) %, 7r°yy = (24.4±5.0)%, 37r° = (17.7±3.5)%.

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1219cross section of 16±3 mb for hydrogen 16 and 96.5=1=8.5 mb for carbon, 17 independent of energy. The loss varied from 17% to 30%, and in the worst case was uncertain by about 9%.Losses due to multiple scattering, decay of kaons in flight, and accidental vetos were calculated in the standard way. Results are given in the table.The quoted statistical error is a combination of the usual counting error and that incurred in the background subtraction. 11 The systematic error combines the error in rj, discussed above, with those in the beam monitoring procedure, effective target thickness, etc. The cross-section results are listed in the table and illustrated in Fig. 6, along with previous results and a calculation based on the resonance model of Gourdin and Dufour. 15 V. CONCLUSIONSThe results of this experiment corroborate the evidence from other experiments that photoproduced A hyperons exhibit a large polarization at 0 c .m. = 9O° in the 1100-MeV region; in addition, they suggest that at higher energies the polarization decreases. The differ-16