Electron-positron angular correlations were measured for the isovector
magnetic dipole 17.6 MeV state (Jπ=1+, T=1) → ground state
(Jπ=0+, T=0) and the isoscalar magnetic dipole 18.15 MeV (Jπ=1+,
T=0) state → ground state transitions in 8Be. Significant
deviation from the internal pair creation was observed at large angles in the
angular correlation for the isoscalar transition with a confidence level of >5σ. This observation might indicate that, in an intermediate step, a
neutral isoscalar particle with a mass of 16.70±0.35 (stat)±0.5
(sys) MeV/c2 and Jπ=1+ was created.Comment: 5 pages, 5 figure