Pontecorvo Reactions

TL;DR

This paper explores the feasibility of measuring Pontecorvo reactions involving antiprotons and helium-3 nuclei at CERN, aiming to distinguish between theoretical models of nucleon interactions within nuclei.

Contribution

It presents a preliminary design and simulation assessment of an experimental setup to measure rare antinucleon annihilation processes on three-nucleon targets.

Findings

Design of a simple detector apparatus using plastic scintillators.

Monte Carlo simulations show promising efficiency in measuring reaction branching ratios.

Assessment of background rejection capabilities for the proposed experiment.

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.