Cuts

 

Table 8.3: The target combinations for fusion yield measurements. Tritium concentration of $c_t=0.1\%$ was used, except the ones marked ($c_t=0.2\%$) and ( ). The layers with bold face were kept fixed during the measurements. Some of the US yield measurements were done with no DS layer.

Yield measurement	US layer (T$\cdot l$)	DS layer (T$\cdot l$)	Time cut
USY	3, 6, 14, (14), (20)	20/ 0	s
MODY	0, 3, 6, 14	20	s
TOFY Series A	14	3, 6, 20	s
TOFY Series B	14	3, 23	s

 

The time cuts for the yield measurements have been chosen to maximize the fusion signal of interest, while avoiding the background. For example, the US and DS fusions, when they coexist, can largely be separated by appropriate time cuts, since most US fusion takes place nearly promptly after the muon stop and disappears with typical time constant of $\sim 100$ns (depending on the tritium concentration), while DS events occurs after $\mu t$ time-of-flight across the drift distance, typically of order $\mu$s. The standard time cuts of s, and s were used for the USY and TOFY measurements, respectively, while the MODY time cuts were slightly varied to maximize the signal-to-background ratio (e.g., with a thin US moderator, the $\mu t$ energy is rather high, hence the time-of-flight short, which could overlap with US fusion). Table 8.3 summarizes the main conditions for the yield measurements.

Together with the partial yields for given time cuts, we give the total yield with the acceptance for the time cut estimated by SMC simulations. These corrections are typically 10% or less. The comparisons with Monte Carlo calculation results, which will be discussed later, will be done using the same time cuts for both the data and MC, hence the time cut efficiencies will cancel in those analyses (assuming the time distribution is predicted correctly by the MC).

The effects of the energy cuts on the yield were carefully studied by using different cuts, as well as estimating the efficiency using a dedicated Monte Carlo. These and other corrections will be discussed later.

  

Figure: Si energy spectra with 3 T$\cdot l$ US D₂ layer in the early time range. Top figures show the fusion signal (filled circles ) and a background run without US D₂ layer (open circles), while bottom figures give background subtracted spectra.

  

Figure: Top: early time Si energy spectra with 14 T$\cdot l$ US D₂ (filled circles) and a pure H₂ background run (open circles). Bottom: background subtracted Si energy spectra. Notice the wider peak and the tail at low energy compared to the 3 T$\cdot l$ measurement in Fig. 8.7.