Elastic Scattering of Muonic Hydrogen Atoms Against Protons: Status of Experiments

Abstract

Let us first recall that, when a negative muon has been slowed down to sufficiently low energy in a hydrogen target, it undergoes the atomic capture process by a hydrogen atom, which leaves the muon in an excited state of the newly formed up system. Due to the fact that the muon interaction with the nucleus is weak, this system is allowed to attain the 1S ground state through different processes (radiative transitions, Auger effects, Stark-mixing collisions), which altogether are referred to as the atomic cascade, and mostly take place within a very short time (≃10⁻¹⁰sec) with respect to the free muon lifetime. When they have de-excited to their 1S level, the electrically neutral μp atoms have exceptionally small atomic dimensions (a_μ = 2.56×10⁻¹¹ cm), are endowed with a kinetic energy E_o (with which they begin to diffuse throughout the surrounding medium) and are initially formed in a statistical mixture of the hyperfine structure states (triplet and singlet, separated by an energy gap ∆E = 0.183 eV).¹