Scattering ofpμmuonic atoms in solid hydrogen

Abstract

We present the results of experimental and theoretical study of the scattering of low-energy p atoms in solid hydrogen cooled to 3 K. Strong effects resulting from the solid state interactions have been observed in the TRIUMF experiment E742 where muons were stopped in thin frozen layers of hydrogen. The resulting emission of low-energy p atoms from the hydrogen layer into the adjacent vacuum was much higher than that predicted by calculations which ignored the solid nature of the hydrogen. New differential scattering cross sections have been calculated for the collisions of p atoms on solid hydrogen to account for its quantum crystalline nature. Analysis of the experimental data performed using such cross sections shows the important role of the coherent scattering in p atom diffusion. For p energies lower than the Bragg cutoff limit (Ϸ2 meV) the elastic Bragg scattering vanishes which makes the total scattering cross section fall by several orders of magnitude, and thus the hydrogen target becomes transparent allowing the emission of cold p atoms to occur.

Differential cross sections for muonic atom scattering in solid hydrogenic targets

“…In particular, a rapid decrease of the total cross section below the Bragg cutoff energy leads to an enhanced emission of cold muonic atoms at temperatures T 5 K, where the phonon annihilation processes are strongly suppressed. The enhanced emission of pµ atoms has been observed and is well described by the calculated differential cross sections [5]. The coherent phonon creation disappears below about 2 meV.…”

“…This leads to a large increase of the aµ mean free path, which results in an enhanced emission of the cold (∼ 1 meV) muonic atoms from the thin solid targets. This phenomenon has been already observed in the TRI-UMF experiment [5], in the case of pµ atoms. When the target temperature is raised, the low-energy phonon processes become more important and, near the melting temperature, the phonon cross section is quite large at ε → 0 (see Fig.…”

“…The analogous cross sections for T = 3 K were presented in Ref. [5,20]. For pµ(F = 1), the incoherent scattering at the lowest energies is more pronounced than in the tritium case since σ inc is comparable to σ coh (cf.…”

“…Townsend minima, which is apparent at about 10 eV. This mechanism has been used for the production of the energetic (1-10 eV) dµ and tµ beams at TRIUMF [1,2,3,4,5,6]. The calculated differential cross sections establish the basis for accurate simulations of the emission of such muonic-atom beams.…”

“…The solid hydrogenic targets have been used for the production of the muonic hydrogen atom beams, which have been applied to the time-of-flight measurements of various muonic-atom and muonic-molecular processes (see e.g., Refs. [1,2,3,4,5,6]). The bulk hydrogenic crystals are employed in the investigations of muon-catalyzed fusion of the hydrogen isotopes at high target densities and for various populations of the rotational molecular levels [7,8,9,10,11,12,13].…”