Argonne National Laboratory

Henry Weller of Duke University will present "Unambiguous Evidence for the Second 2+ State in 12C Obtained Using the 12C + g → 3a Reaction at the HIyS Facility."

Abstract:
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 HIS 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 HIS facility will also be presented.