Improvements and Future directions

One of the difficulties of our time-of-flight measurements was its low event rate. Although our accuracy for the molecular formation rate is not dominated by the statistical uncertainty, the small size of the fusion data sample made it difficult for us to investigate thoroughly the systematic effects such as background subtraction. More data would help us to understand these effects better, and reduce the uncertainties.

At the present moment, theoretical uncertainties due to solid state effects give a large contribution to our total uncertainty. It is hoped that the situation will be improved in the near future, as theoretical efforts are underway. As discussed in Appendix B, the evaluation of the back-decayed $\mu t$ energy would be necessary to significantly improve the accuracy of our measurements.

For better determination of the RT energy and $d\mu t$ resonance energy, more precise knowledge of the target spacing distance would be required. Measurement in-situ of the distance is not trivial in our setup, and appropriate methods should be investigated. Some minor modification of our gold target support (e.g., using a flat plate rather a than very thin foil for the DS) could help to better define this distance.

As a future project for our collaboration, I have spent a considerable amount of effort in the past few years, together with Peter Kammel and Glen Marshall, in developing a new method for a direct measurement of the sticking probability using the multilayer solid targets [179,237,171]. Sticking, as discussed in Chapter 1, places the most stringent limit on the fusion yield per muon, hence, has attracted much attention in this field, but the discrepancy between experiment and theory persists to date. Most previous experiments are sensitive to the final sticking, which is a combination of initial sticking and stripping, hence cannot be readily compared with theory. Taking advantage of our multilayer target, we propose to (a) experimentally separate initial sticking and stripping, and (b) unambiguously determine sticking at high density where the $\mu$CF efficiency is highest, but the discrepancy is largest. The experiment is already approved by the TRIUMF Experimental Evaluation Committee, but our situation is a little unclear due to funding difficulties. The further discussion of this experiment is beyond scope of this thesis and interested readers are referred to Refs. [179,237,171].