Recently, we observed an anomalous internal pair creation for the M1 transition depopulating the 18.15 MeV isoscalar 1 + state in 8 Be. The deviation from the theoretical prediction can be described by assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/c 2 . In order to clarify the interpretation, we re-investigated the 8 Be anomaly with an improved and independent setup. We have confirmed the signal of the assumed X(17) particle and constrained its mass (m 0 c 2 = 17.01(16) MeV) and branching ratio compared to the γ-decay (B x = 6(1)× 10 − 6 ). We investigated also the high-energy (21 MeV) J π = 0 − → 0 + transition in 4 He and got a consistent result for the X(17) particle.
ASJC Scopus subject areas
- Physics and Astronomy(all)