Novel insights into transfer processes in the reaction 16O+208Pb at sub-barrier energies

TL;DR

This study reveals that in the $^{16}$O+$^{208}$Pb reaction at sub-barrier energies, two-proton transfer is highly enhanced due to pairing correlations, indicating possible supercurrent behavior of proton pairs.

Contribution

It provides new experimental evidence of strong two-proton pairing correlations and potential supercurrent phenomena in nuclear transfer reactions at sub-barrier energies.

Findings

Two-proton transfer probability exceeds expectations for uncorrelated protons.

Two-proton transfer probabilities are comparable to one-proton transfer near the fusion barrier.

Evidence suggests the presence of a nuclear supercurrent of proton pairs.

Abstract

The collision of the doubly-magic nuclei $^{16}$O+$^{208}$Pb is a benchmark in nuclear reaction studies. Our new measurements of back-scattered projectile-like fragments at sub-barrier energies show show that transfer of 2 protons ($2p$) is much more probable than $\alpha$-particle transfer. $2p$ transfer probabilities are strongly enhanced compared to expectations for the sequential transfer of two uncorrelated protons; at energies around the fusion barrier absolute probabilities for two proton transfer are similar to those for one proton transfer. This strong enhancement indicates strong $2p$ pairing correlations in $^{16}$O, and suggests evidence for the occurrence of a nuclear supercurrent of two-proton Cooper pairs in this reaction, already at energies well below the fusion barrier.