Unexpectedly enhanced $\alpha$-particle preformation in ${}^{48}$Ti probed by the $(p,p\alpha )$ reaction

Abstract

The formation of $\alpha$ particle on nuclear surface has been a fundamental problem since the early age of nuclear physics. It strongly affects the $\alpha$ decay lifetime of heavy and superheavy elements, level scheme of light nuclei, and the synthesis of the elements in stars. However, the $\alpha$-particle formation in medium-mass nuclei has been poorly known despite its importance. Here, based on the ${}^{48}\mathrm{Ti}(p,p\alpha {)}^{44}\mathrm{Ca}$ reaction analysis, we report that the $\alpha$-particle formation in a medium-mass nucleus ${}^{48}\mathrm{Ti}$ is much stronger than that expected from a mean-field approximation, and the estimated average distance between $\alpha$ particle and the residue is as large as 4.5 fm. This new result poses a challenge of describing four nucleon correlations by microscopic nuclear models.

Comments: 6 pages, 4 figures