Neutralization of excited antiprotonic helium ion in collisions with helium atoms

Abstract

We consider a neutralization of excited antiprotonic helium ion accompanied by antiproton transitions to lower states in collisions with helium atoms $(\bar{p}\mathrm{He}^{2+})_{nl} + \mathrm{He} \rightarrow \left[ (\bar{p}\mathrm{He}^{2+})_{n_f l_f} e\right]_{1s} + \mathrm{He}^+$ in low-temperature medium. Interactions in the input and output channels are taken similar to the potentials of $\mathrm{H}^+ - \mathrm{He}$ ($X^1\Sigma$) and $\mathrm{H} - \mathrm{He}^+$ ($A^1\Sigma$) systems, respectively. The final term is shifted down by the antiproton transition energy. Therefore initial and final terms can intersect for the suitable antiproton quantum numbers leading to an appreciable cross sections of the transitions. We have found that this process can provide an additional increase of effective annihilation rates for highly excited antiprotonic helium ion even in the low-density and temperature target corresponding to known experimental conditions.