Determination of the ratio σ(p̄n)/σ(p̄p) from p̄4He reaction data

The ratio R a b between the cross sections for the annihilation of p on n and on p bound in the 4 He nucleus at four p momenta (at rest, 192.8, 306.2 and 607.7 MeV/ c ) has been obtained by the analysis of p 4 He annihilation events detected with a self-shunted streamer chamber exposed to the LEAR p beams. R a b increases from 0.42 ± 0.05 at rest up to 0.66 ± 0.09 at 607.7 MeV/ c . The results are discussed in the light of Glauber theory analyses of p 2 H and p -nucleus data.