Pontecorvo Reactions

Abstract

Pontecorvo reactions are rare antinucleon annihilation processes that are forbidden on free nucleons but allowed on nucleons bound within nuclei. The interest in studying this phenomenon lies in its potential to provide insights into the annihilation mechanism and, particularly, the short-distance dynamics between nucleons within the nucleus. Some measurements were performed in the past at CERN's Low Energy Antiproton Ring (LEAR) using antiprotons annihilating on a deuterium target. However, no data exist for targets consisting of three nucleons, such as $^3\text{He}$ or $^3\text{H}$. The measurement of the rate of the process $\overline{p} \, ^3\text{He} \rightarrow p + n$ would allow for distinguishing between different theoretical models whose predictions vary by 1-2 orders of magnitude. The ASACUSA collaboration is studying the feasibility of performing this measurement at CERN's ELENA-AD. A preliminary design of a simple measurement apparatus, utilizing plastic scintillators and degrader layers, is presented, together with Monte Carlo simulations assessing its efficiency in measuring the branching ratios of the aforementioned reaction and rejecting background from more probable typical antiproton annihilations in the target.