Measurement of the Δ−−Δ++ electromagnetic mass difference

Abstract The Δ − −Δ ++ isobar mass difference has been measured in a deuterium bubble chamber from the reactions π − p→ π + π − n and π + n→ π − π + p at incident momentum 555 MeV/ c . The value obtained for Δ − − Δ ++ is 5.9 ± 3.1 MeV. The error is a factor of two smaller than that from the previous experiment.