Chernykh M, Feldmeier H, Neff T, von Neumann-Cosel P, Richter A
Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany.
Phys Rev Lett. 2007 Jan 19;98(3):032501. doi: 10.1103/PhysRevLett.98.032501. Epub 2007 Jan 17.
The first excited 0(+) state in 12C (Hoyle state) has been predicted to be a dilute self-bound gas of bosonic alpha particles, similar to a Bose-Einstein condensate. To clarify this conjecture, precise electron scattering data on form factors of the ground state and the transition to the Hoyle state are compared with results of the fermionic molecular dynamics model, a microscopic alpha-cluster model, and an alpha-cluster model with reduced degrees of freedom (in the spirit of a Bose-Einstein condensed state). The data indicate clearly a dilute density with a large spatial extension of the Hoyle state. A closer inspection of the model calculations, which reproduce the experimental findings, reveals that the term Bose-Einstein condensation of three alpha particles must not be taken too literally.
