Nitrogen contamination

If there was a contamination of heavier elements in the emission layer, the yield of $\mu t$ would be reduced due to muon transfer from the proton to the heavy element. In some of the runs, we observed muonic X rays from muonic nitrogen atomic transitions, indicating contamination of the target. From the analysis of the Lyman series X rays, the contamination level was estimated to be a few ppm level by Francoise Mulhauser [83,231]. In the constant rate, infinite medium approximation, the probability of $\mu t$ production can be expressed as:

where c_N2 is the concentration of N₂ molecules, and the muon transfer rate from a proton to a nitrogen atom. Using the proton to triton transfer rate $\mu$s^-1, and $p\mu p$ formation rate $\mu$s^-1, both obtained from our earlier measurements in solids [83], together with the transfer rate to nitrogen s from Ref. [232] (measured in a gas), we can estimate the reduction factor for the $\mu t$ production , which is normalized to the pure target yield . Table 8.12 presents the correction factor for two series of target sets which are of relevance in our analysis.

 

Table 8.9: The $\mu t$ production probability with possible nitrogen contamination, and the reduction factor , normalized to a pure emission target .

Target	ID	cN2 (Ref. [231])
SETct=0.1% (a)	II-1 to II-4	3.3+6.8-3.3 ppm	0.621+0.14-0.28
SETct=0.1% (b)	II-6 to II-11	2.3+4.6-2.3 ppm	0.611+0.11-0.23

 

We note that the estimate of nitrogen contamination by Mulhauser gives asymmetric errors as quoted in the table, but we take the average of two extreme values of 1$\sigma$ error bars for convenience in the data treatment. In our analysis, we assume that reduction in $\mu t$ emission is proportional to the factor given here, neglecting the effects of the transfer, which is presumably much smaller.