Observation of oscillations and near-barrier suppression in the fusion of $^{20}$O + p

TL;DR

This study reports the first measurement of the fusion excitation function for $^{20}$O + $^1$H, revealing oscillatory behavior near the barrier and highlighting the importance of low-angular-momentum states and coupled channel effects.

Contribution

First experimental measurement of $^{20}$O + $^1$H fusion excitation function, demonstrating oscillations and near-barrier suppression, supported by R-matrix coupled channel calculations.

Findings

Observed oscillations in fusion cross section near the barrier.

R-matrix coupled channel calculations reproduce oscillations.

Failure of one-channel calculations to match sub-barrier suppression.

Abstract

Using an active target detector, the fusion excitation function for $^{20}$O + $^1$H was measured for the first time. Near the barrier, the fusion cross section manifests an oscillatory behavior with broad peaks $\sim$50-100 keV wide. The presence of these peaks likely reflects the low density of low-angular-momentum states in the quasibound regime. R-matrix coupled channel (CC) calculations that include the first excited 2$^+$ state in $^{20}$O are able to reproduce the observed oscillations. However, one channel CC calculations fail to reproduce the decrease in the sub-barrier cross section experimentally observed.