THE BINDING ENERGY DIFFERENCE BETWEEN THE HYPERNUCLIDES 4HE SUB LAMBDA AND 4H SUB LAMBDA.

Abstract : Experimental and theoretical studies indicate a departure from charge symmetry for the mirror hypernuclides 4He sub lambda and 4He sub lambda amounting to a few tenths of a MeV in the binding energies. A nuclear emulsion experiment utilizing 45 newly measured pion(-) mesic decays of 4He sub lambda and 4H sub lambda is reported to give delta B sub lambda = B sub lambda (4He sub lambda) -B sub lambda (4H sub lambda) = (0.55=0.26) MeV. Contamination by other hypernuclides (probably 5He sub lambda) was eliminated from the 4He sub lambda sample by a strict recoil-range requirement (R> or = 10 micro. m), while, on the other hand, no contaminants were found among the 4H sub lambda decays. The binding energy discrepancy between the pion-r and pion-pr decays of 4H sub lambda was found to be due to pion range measurement losses which are important mainly for the pion-r events (R sub pi = 4 cm). The final value of delta B sub lambda for the latter sample is (0.30=0.14) MeV. Because a negative term in the theoretical calculation of delta B sub lambda is expected from a Coulomb energy increase in the 3He core of 4He sub lambda, this positive experimental result is a strong indication of charge-symmetry violation in the lambda hyperon N interaction compatible with estimates of the virtual electromagnetic effects in (lambda hyperon to lambda hyperon + pion) suggested by theoretical workers.