Neutralization of excited antiprotonic helium ion in collisions with helium atoms

Abstract

We consider the neutralization of an excited antiprotonic helium ion which is accompanied by antiproton transitions to lower states during 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 a low-temperature medium. Interactions in the input and output channels are taken to be similar to the potentials of the $$\mathrm {H}^+ - \mathrm {He}$$ ( $$X^1\varSigma ^+$$ ) and $$\mathrm {H} - \mathrm {He}^+$$ ( $$A^1\varSigma ^+$$ ) systems, respectively. The potentials in the output channels are shifted by an amount equal to the dexcitation energy of the antiproton. Therefore, the potentials in the input and output channels can intersect for the some antiproton quantum numbers leading to appreciable cross sections of the transitions. We have found that this process can increase the effective annihilation rates of highly excited antiprotonic helium ions in helium targets of low atomic density and temperature that were used in recent experiments.