Sticking is a process in which the muon becomes attached to a positively charged fusion product such as an particle. The probability of the process, denoted by , imposes a more stringent limit on the efficiency of CF than the short lifetime of the muon itself, hence it has attracted much attention, but discrepancy between experiments and theory persists, motivating further investigation.
Sticking takes place in two distinct steps:
The experimental results on sticking have been in disagreement with theory and, sometimes, with each other. The challenge lies in its low branching ratio and in the handling of tritium. Figure 1.3 summarizes the previous measurements of final sticking plotted against target density . Apart from a longstanding discrepancy on the density dependence between two major experimental groups at PSI and LAMPF, in which the analysis of the latter now appears to be unreliable at low densities, most experimental values are systematically and substantially smaller than the theoretical prediction, even though different methods have been used. For a recent review, see Ref. .