Unambiguous evidence for the second 2⁺ state in ¹²C obtained using the ¹²C + γ → 3 α reaction at the HIγS facility

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(γ,α)⁸Be reaction using the intense, nearly mono-energetic γ-ray beams available at the HIγS facility and an optical time-projection-chamber to detect the outgoing α-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 HIγS facility will also be presented.

Argonne Physics Division Seminar Schedule