The Hoyle State in Relativistic ${}^{12}$C Dissociation.

Production of $\alpha$-particle triples in the Hoyle state (HS) in dissociation of ${}^{12}$C nuclei at 3.65 and 0.42 $A$ GeV in nuclear track emulsion is revealed by the invariant mass approach. Contribution of the HS to the dissociation ${}^{12}$C $\to$ 3$\alpha$ is (11 $\pm$ 3) \%. Reanalysis of data on coherent dissociation ${}^{16}$O $\to$ 4$\alpha$ at 3.65 $A$ GeV is revealed the HS contribution of (22 $\pm$ 2) \%.