Fusion of O 16 + Ho 165 at deep sub-barrier energies

Fusion cross sections have been measured for the asymmetric system $^{16}\mathrm{O}+^{165}\mathrm{Ho}$ at energies near and deep below the Coulomb barrier with an aim to investigate the occurrence of fusion hindrance for the system. Cross sections down to $\ensuremath{\approx}700$ nb have been measured using the off-beam $\ensuremath{\gamma}$-ray technique. The fusion cross sections have been compared with the coupled channel calculations. The energy onset of fusion hindrance appears to occur at ${E}_{\mathrm{c}.\mathrm{m}.}=57\ifmmode\pm\else\textpm\fi{}0.85$ MeV, where a deviation in the slope of the experimental logarithmic derivative compared to that of coupled channel calculations has been observed. This is in agreement with the value obtained from the touching point configuration of the adiabatic model.