Unambiguous Evidence for the Second State
The second 2+ state in 12C, predicted to exist over fifty years ago as an excitation of the Hoyle state, has been unambiguously identified in the 12C(ya8) Be reaction using the intense, nearly mono-energetic -ray beams available at the HIS facility and an optical time-projection- chamber to detect the outgoing -particles.
E1 and E2 cross sections as well as their relative phases were determined from complete angular distributions measured between 9.1 and 10.7 MeV. In addition to the structure in the cross section, the behavior of the relative phase confirms the existence of the second 2+ state in 12C. The energy, width and B(E2) to the ground state were determined. Possible implications on the structure of the Hoyle state will be discussed. A brief summary of the current and near-future performance characteristics of the HIS facility will also be presented.