Measurement of isospin mixing in /sup 4/He and its implications for charge-symmetry breaking

..pi..-/sup 4/He inelastic cross sections have been measured at T/sub ..pi../ = 180 MeV. In the region of the J/sup ..pi../ = 1/sup -/ states (E/sub x/approx. =23 to 30 MeV) the ..pi../sup +//..pi../sup -/ cross-section ratio R/sub ..pi../ was found to be 1.05 +- 0.08 at theta/sub lab/ = 30/sup 0/. Such a small deviation from 1.0 implies that isospin mixing between the T = 0 and T = 1 states in /sup 4/He is quite weak, in striking contrast to the strong isospin mixing deduced from the large ratio of photonucleon cross sections, R/sub ..gamma../ = sigma(..gamma..,p)/sigma(..gamma..,n)approx. =1.7. Thus the conclusion drawn from the photonucleon work, that there is a large charge-symmetry-breaking nuclear force in /sup 4/He, needs to be reexamined.