Search for a possible J^π = 0⁺, T = 2 resonance in ⁹Be(τ, γγ)¹²C

A 50 cm³ Ge(Li) detector has been used to re-examine the reaction ⁹Be(τ, γγ)¹²C over a previously reported resonance at E(τ) = 1.739±0.007 MeV which was suggested as the lowest T = 2 state in ¹²C. This state is expected to γ-decay via the 1⁺, T = 1 state at 15.11 MeV. However a search with τ bombarding energies ranging two standard deviations above and below the reported resonance energy revealed no resonance in high-energy γ-rays. An upper limit of Γ_τΓ_γ/Γ < 2.0 meV is established for the T = 2 resonance strength which is one-fourth of the previously reported strength and which strongly corroborates an additional negative result reported as Γ_τΓ_γ/Γ < 1.5 meV. In the course of the experiment a new value of Γ_lab = 2.94±0.20 keV was obtained for the resonance at E_p = 1.083 MeV in ⁹Be(p, γ)¹⁰B.